S M Maca

A W Schiesser

A Sobala

K Gruber

G Pakesch

C Prause

Dr T Barisani-Asenbauer

Distress, depression and coping in HLA-B27-associated anterior uveitis with focus on gender differences

Keywords: depression, coping skills, distress, gender, anterior uveitis

Background/aims: To evaluate depression, coping with disease and stress, and the subjective impression of distress and/or life events as triggers for recurrences in HLA-B27-associated anterior uveitis (B27-AU), with attention to gender-specific characteristics.

Methods

: 171 patients with a history of B27-AU responded to a postal survey performed between January 2006 and April 2008 using standardized psychological questionnaires: Beck Depression Inventory (BDI), Freiburg Questionnaire on Coping with Illness (FQCI), and Stress Coping Inventory (SCI).

Results: Patients with B27-AU differed from healthy controls showing more depressive symptoms (BDI, 31.6%), applying characteristic disease coping as well as negative stress coping strategies. Female B27-AU patients tended to react with depression, males to use negative stress coping strategies. 57.9% of patients believed in psychological distress as a trigger for relapses, 34.5% stated specific life events. Together, this group of patients achieved higher depression scores and used more negative disease and stress coping styles than patients without perception of distress.

Conclusion:

B27-AU patients exhibited significant psychopathology concerning depression and disease coping. Distress and life events were subjectively suspected to be a trigger. By imparting knowledge to the patients upon probable development of depressive moods and the role of stress/life events as trigger for relapses, as well as offering behavior therapy to optimize coping may help to better deal with B27-AU.

Uveitis associated with the HLA-B27 antigen (B27-AU) is an acute-onset, painful eye disease with a relapse risk of up to 74%. [START_REF] Power | Outcomes in anterior uveitis associated with the HLA-B27 haplotype[END_REF] The treatment consists of antiinflammatory topical and systemic therapy as well as pharmacologic cycloplegia for reduction of pain and prevention of synechiae. At each recurrence the pain, as well as the deterioration of visual acuity due to inflammation and impaired accommodation pose a strain for the patients. Furthermore, they may require sick leave for several days, lose their ability to perform certain tasks (i.e. reading, working on a computer, driving), and face a risk of losing their jobs. The fact that a patient with a history of B27-AU is at permanent risk for a relapse of disease, associated with pain and fear of a transient or even persistent loss of vision, causes omnipresent distress (negative forms of stress, compared to positive forms of stress = eustress) and poses a chronic psychological burden. For rheumatic diseases in general, as well as for ankylosing spondylitis in particular, a higher prevalence of depression has been reported. [START_REF] Stoltz | Depression in the patient with rheumatologic disease[END_REF][START_REF] Barlow | Gender, depression, and ankylosing spondylitis[END_REF] In a pilot study, Franke et al dealt with the psychopathology of patients with various forms of uveitis and pointed out the importance of evaluating psychological interventions for rehabilitation. [START_REF] Franke | Rehabilitation-psychological aspects of uveitis[END_REF] But, distress does not only play a role as a consequence of disease.

Psychological stress also has been discussed as a probable trigger for uveitis, as patients often report the onset of relapses during or after periods of increased psychological pressure causing a negative mood. Specific life events can cause such distress and therefore have been investigated in this context. So far, clinical studies on uveitis have yielded disparate results. [START_REF] Franke | Rehabilitation-psychological aspects of uveitis[END_REF][START_REF] Schlaegel | Psychopathology in adults with uveitis[END_REF][START_REF] Erbaugh | Emotional factors in uveitis: a pilot study[END_REF][START_REF] Heaton | An Ecologic Approach To Uveitis[END_REF][START_REF] Sen | Endogenous uveitis in relation to stress--a clinical study[END_REF][START_REF] Kumar | Stress and uveitis[END_REF][START_REF] Secchi | A psychosomatic approach to idiopathic recurrences of anterior uveitis[END_REF][START_REF] Mayer | Psychosomatic aspects of uveitis in the context of working life[END_REF][START_REF] Mulholland | Anterior uveitis and its relation to stress[END_REF][START_REF] Schiffman | Visual functioning and general health status in patients with uveitis[END_REF][START_REF] Carrim | The relationship between stress and acute anterior uveitis[END_REF] Concerning other auto-immune diseases, such as multiple sclerosis or Behcet's disease, stressful life events were shown to represent an aggravating factor , as they resulted in a significant increase in risk of disease exacerbations. [START_REF] Mohr | Association between stressful life events and exacerbation in multiple sclerosis: a meta-analysis[END_REF][START_REF] Karlidag | Stressful life events, anxiety, depression and coping mechanisms in patients with Behcet's disease[END_REF] The aim of the present study was to evaluate the role of distress as a trigger from the patients' point of view, as well as to objectively evaluate the presence of depressive moods and the strategies used to cope with disease and stress. We decided to include only patients with a history of anterior uveitis associated with the HLA-B27-antigen, to obtain a large and homogenous patient population. A further point of interest was to delineate gender-specific differences. The results could help to gain further insight into the psychopathology of B27-AU and underline the importance of psychological interventions.

MATERIALS AND METHODS

Patient recruitment

This clinic-based, cross-sectional study was performed at the uveitis unit of the Department of Ophthalmology, Medical University of Vienna, from January 2006 to April 2008. A written invitation to participate in the study via a postal survey was sent once to 381 B27-AU-patients who had been treated at the uveitis unit since 1980.

171 patients (45%) with recent and/or recurrent history of acute B27-AU responded with a completed questionnaire and were included in the study. Patients had to indicate whether an acute relapse was present or not. Institutional review board approval and informed consent were obtained in accordance with the Declaration of Helsinki. The booklet containing the questionnaires was prefaced by a general invitation letter explaining the scientific character of the survey and that the participation was voluntary. Patients were informed that the impact of stress on disease coping in patients with AU should be studied, the expressions "gender", "depression" and "trigger" were not used. Normative values were obtained in an ethnicity-and aged-matched control group of 55 healthy individuals (mean age=45.6±10.1 yrs, p=0.1).

The survey consisted of 3 psychometric instruments, listed below, as well as questions related to sociodemographic data (gender, age) and uveitis details (age at onset of uveitis, number of recurrences in total and approx. per year, the approx. duration of attacks and interval since the last recurrence, coexistence of a B27associated spondylarthropathy). Furthermore, patients were questioned upon the presence of psychological factors before an attack. Patients could indicate specific live events, which subjectively were suspected to be connected with a relapse.

Psychometric instruments

The Beck Depression Inventory (BDI) is a self-report inventory for differentiation of a clinically relevant depressive mood. [START_REF] Beck | Beck-Depressions-Inventar Bern[END_REF] Twenty questions document the actual severity of depressive moods, indicated by a sum score (0-63 points). The sum score also is allocated to one of 3 clinically relevant groups: "not depressed" (0-9 points), "minimal depressive mood" (9 to 19 points), and "clinical relevant depressive mood" (19-63 points).

Coping was assessed by the Freiburg Questionnaire on Coping with Illness (FQCI). [START_REF] Muthny | Freiburger Fragebogen zur Krankheitsverarbeitung Weinheim[END_REF] This 35-item questionnaire is used to calculate 5 primary dimensions (subscales): "depressive coping", "problem-solving behavior", "distraction and selfrevalorization" (encouraging oneself), "religiousness/quest for meaning" (each 5-25 points), and "cognitive avoidance/ dissimulation" (trivializing and wishful thinking, 3-15 points). A high score in a FQCI subscale indicates a strong tendency to apply this type of coping mechanism.

Coping was also assessed by the Stress Coping Inventory (SCI) questionnaire, which consists of 114 items. [START_REF] Jahnke | Stressverarbeitungsfragebogen 120[END_REF] Item scores (each 0-4 points) are grouped to calculate 19 subscales that describe various coping strategies (combination of 6 item scores, 0-24 points). Alternatively, the items may also be classified into 2 secondary dimensions, namely "negative" or "positive coping" strategies (0-24 points).

Statistics

The SPSS 16.0 software was used for statistical analysis. For descriptive analysis, data are expressed as total numbers (n), percentage relating to group (%), means ± standard deviation (SD). The Kolmogorov-Smirnoff-test was used to test for standard distribution, the T-test or Mann Whitney U-test was used as appropriate. The cut-off level for statistical significance was set at p<0.05; all tests were performed in a twotailed manner. In case of multiple testing within a group (gender-comparisons concerning BDI items, FQCI and SCI), a Bonferroni-Holm correction for adjustment of the p-value was applied. [START_REF] Holm | A Simple Sequentially Rejective Multiple Test Procedure[END_REF]

RESULTS

171 patients with known HLA-B27 antigen-associated uveitis, 64 women and 107 men, returned the questionnaires. The gender distribution was calculated to be female: male = 1:1.7 (p<0.001, table 1). 13 patients (7.6%) had active recurrence at the time of answering the questionnaire, in 75 patients (43.9%) a B27-associated spondylarthropathy was existent. Altogether, the patients had suffered from approximately 12.9±20.1 uveitis relapses since disease onset, which had been 14.3±9.6 years ago. More information concerning uveitis recurrences is given in table 1. No differences in sociodemographic data were found comparing patients who responded to the survey and those who did not.

Beck Depression Inventory (BDI)

The mean total score obtained in patients with B27-AU was significantly higher than the value obtained from the control group (8.7±7.0 and 4.4 ±4.3 respectively, p<0.001, table 2, figure 1). Patients with an acute relapse scored even worse (11.3±7.7, p=0.19), the coexistence of an additional spondylarthropathy did not affect the score (9.5±7.6, p=0.13). 31.6% of B27-AU patients (n=54) were above "normal range", as 19.3% were classified to be in a "minimal depressive" and 12.3% in a "clinical relevant depressive" mood.

36% of women and 28.9% of men exhibited depressive moods (p=0.34), the mean total sum score was slightly higher in the female group (table 2). In female and male B27-AU patients the scores were significantly higher than those of the corresponding healthy comparison groups (table 2, figure 1). Concerning the individual test items women suffered more from "loss of libido" than men (w=2.00±1.03, m=1.57±0.76, p=0.002). B27-AU patients exhibited different patterns than controls concerning 3 of 5 coping styles. They tended towards "cognitive avoidance and dissimulation" (p<0.001, table

2), women as well as men. Women in particular seemed to lose the ability for "distraction and self-revalorization" (p=0.030), men tended to apply a "problemsolving behavior" (p=0.004).

German Stress Coping Inventory (SCI)

Compared to healthy controls, B27-AU patients reached higher scores on 4 of 19 subscales, leading to a statistically significant increase of the secondary dimension negative coping (table 2, p=0.005). Splitting these findings according to gender, female patients seemed to less "play down the disease" (p=0.030), needed more "social support" (mean score was significantly higher than in B27-AU males although should have been similar), used less "self-medication" (p=0.005), but reacted with more "rumination" (p=0.020) than healthy controls. Male patients also tended to use "rumination" (p=0.003), but in addition exhibited aggravated patterns in 8 more subscales, displayed in table 2. Summarized, these patterns are reflected in an elevated score of "negative coping" in males (p=0.002).

Distress and/or life events as triggers for B27-AU relapses 57.9% of patients (n=99, p<0.001) had the impression that psychological factors had an influence in the sense of triggering B27-AU, women more often than men (p=0.045, figure 2). 34.5% could even state specific life events after which an attack had occurred (table 3). Patients, who had mentioned psychological stress +/-a life event ("distress"-group), exhibited raised and depressive BDI sum scores (distress=10.1±7.9, no distress=7.1±5.4, p=0.008). The same finding was true when assessing only women (p=0.042) or men (p=0.056). These patients also reached higher scores for depressive coping on the FQCI (distress= 11.4±4.3, no distress= 9.7±3.9, p<0.001), independent of gender (w=11.6±3.7, m=11.5±4.8, p=0.961). On the SCI a difference was found for 3 of the 19 subscales (more resignation, more rumination, less playing down the disease, all p<0.001), together resulting in an elevated score of negative coping (distress=10.9±4.4; no distress= 8.3±3.6, p<0.001).

DISCUSSION

From the 1960's onwards a number of studies discussed a connection between distress or depressive tendencies and uveitis (table 4). [START_REF] Franke | Rehabilitation-psychological aspects of uveitis[END_REF][START_REF] Schlaegel | Psychopathology in adults with uveitis[END_REF][START_REF] Erbaugh | Emotional factors in uveitis: a pilot study[END_REF][START_REF] Heaton | An Ecologic Approach To Uveitis[END_REF][START_REF] Sen | Endogenous uveitis in relation to stress--a clinical study[END_REF][START_REF] Kumar | Stress and uveitis[END_REF][START_REF] Secchi | A psychosomatic approach to idiopathic recurrences of anterior uveitis[END_REF][START_REF] Mayer | Psychosomatic aspects of uveitis in the context of working life[END_REF][START_REF] Mulholland | Anterior uveitis and its relation to stress[END_REF][START_REF] Schiffman | Visual functioning and general health status in patients with uveitis[END_REF][START_REF] Carrim | The relationship between stress and acute anterior uveitis[END_REF] Nevertheless, these studies draw opposite conclusions. Various uveitis entities being grouped together, small sample sizes, and the diversity of evaluation instruments (such as personal interviews versus questionnaires) may have led to these diverse results, difficult to be compared with each other. To overcome these limitations of previous studies we concentrated on a well defined and homogenous uveitis entity and used only standardized questionnaires.

One aim of our study was to evaluate the patients' subjective impression of life events and psychological distress as a trigger for recurrences of HLA-B27 positive anterior uveitis. In our study population, 57.9% of the patients reported life events and psychological distress as a potential triggers. Theories, that distress might negatively influence the immune system via the neuro-endocrine system could be an explanation for a connection between distress and disease exacerbation, but are not investigated closely enough to draw definite conclusions. [START_REF] Connor | Factors related to the initiation and recurrence of uveitis. XL Edward Jackson memorial lecture[END_REF] Distress might play a role before an attack of B27-AU, but definitely plays a role in the time afterwards.

Future studies will have to investigate both topics, as too many interactions still remain unclear.

Furthermore, the presence of depressive symptoms, disease and stress coping strategies were analyzed using standardized and validated questionnaires. A special focus was set on analyzing gender-specific differences. The male:female ratio of 1.7:1 is comparable to the findings of previous studies on B27-AU patients. [START_REF] Tay-Kearney | Clinical features and associated systemic diseases of HLA-B27 uveitis[END_REF] Test results indicating the presence of depressive moods were found in 31.6% of patients. These results support the data reported by Carrim et al, according to whom patients with acute AU experience an extraordinary burden in terms of their psychological well-being and general health (table 4). [START_REF] Carrim | The relationship between stress and acute anterior uveitis[END_REF] The patients investigated in that study achieved higher (i.e. poorer) scores on the General Health Questionnaire (GHQ) than did controls. The GHQ is a psychometric instrument measuring stress, social dysfunction and depression, and is therefore comparable with the BDI used in our study.

With regard to disease coping, we found specific behavior patterns attributable to both sexes ("cognitive avoidance"), but also gender-specific ones. Franke et al, who studied psychosomatic aspects of 51 patients with various forms of uveitis in a pilot study, concluded that uveitis patients apply specific coping strategies, have a lower disease-specific quality of life and suffer from greater psychological distress (table 4). [START_REF] Franke | Rehabilitation-psychological aspects of uveitis[END_REF] Our results thus provide another informative basis concerning B27-AU patients.

Concerning gender-specific differences, women appear to suffer more from the psychological strain caused by B27-AU than men, which is demonstrated by specific behavior patterns. In comparison to males, women exhibited a tendency towards depressive moods, with a strong bodily component as reflected in increased "loss of libido". A possible explanation for these results could be the knowledge that women are more sensitive to pain than men. In diseases associated with chronic pain women achieve higher scores concerning depression and dejection. [START_REF] Schiesser | Multimodel Treatment of Chronified, Non Malignant Pain and its Influence on Pain Behavior, Social and Psychological Aspects[END_REF] Behavioral patterns during stressful situations also differed between genders (SCI), although findings in females were not as noticeable as in males. Male B27-AU patients exhibited predominantly negative coping strategies. This underlines the importance to differentiate between female and male patients, to then be able to offer a gendertailored supportive approach.

As a probable limitation of the study the participation rate of 45% has to be discussed. According to various authors the response rates to postal surveys rarely exceed 50% [START_REF] Nakash | Maximising response to postal questionnaires--a systematic review of randomised trials in health research[END_REF][START_REF] Asch | Response rates to mail surveys published in medical journals[END_REF], especially if no factors apply which are known to increase compliance (short questionnaires, complex follow-up procedures such as telephone contacts or re-sending the questionnaire or offering a monetary incentive).[ 24 26] None of the latter was used in our study, thus explaining the response rate achieved.

Other problems in studies using questionnaires are those of social desirability bias and concealment of sensitive information. Besides the fact that these apply rather to personal or telephone interviews than to postal surveys, care was taken to compose an invitation letter without suggestive questions. We therefore believe that patients suffering from more versus fewer symptoms were addressed equally and our results

are not biased in that way.

In conclusion, the results of our study indicate that patients with a history of B27-AU are at risk to suffer from depression and tend to use negative coping strategies. According to gender, patients are endangered to encounter specific and sustained psychological problems. A significant proportion of patients believed in psychological distress or life events as a potential trigger for recurrences. These results show that the management of uveitis patients should encompass not only standardized treatment strategies of the ocular disease itself, but also clear information about the relapsing nature of B27-AU, the potential role of distress or life events as triggers, and the disease's impact on psychological well-being. In addition, whenever possible a behavior therapy focused on cognitive styles could be proposed to support the patients' effort and success in dealing with the disease. Through identification of situations causing personal distress, patients can learn to either fight or "flight" specific situations, depending upon individual coping patterns. To recognize the body's tendency towards highly charged states in distress situations, and to alter behaviour accordingly, can reduce the length of time a person suffers from distress, and reduce the body's continued need to produce adrenaline to cope with danger that does not really exist. Improving coping mechanisms in the therapeutic sense can involve meditation, Jacobson's progressive muscle relaxation, cognitive behavioural therapy, and recognition of the body's inappropriate response to distress (e.g. biofeedback).

Altogether, our findings confirm the need for an interdisciplinary and gendertailored management of B27-AU that combines conventional treatment of uveitis with psychological counseling or guidance.

LEGENDS FOR DISPLAY ITEMS Figure 1 Results of the Beck Depression Inventory (BDI)

The BDI sum score was slightly higher in female (9.5±7.6) than in male B27-AU patients (8.4±6.7, p=0.34). Both gender-groups reached scores significantly higher than those of healthy controls (females= 4.5±4.0, p=0.004 and males=4.1±4.

Table 1 Patient characteristics concerning sociodemographics and history of B27 antigen-associated anterior uveitis

 1

		Total patient
		population	Women	Men
	Number of patients	171	64 (37.4%)	107 (62.6%)*
	Current age
		48.8 (14.1)	46.6 (14.9)	50.2 (13.4)
	(years±SD)

Legend: Data are given as total numbers or means; standard deviation (SD) or percentage relating to groups is given in parentheses; † as subjectively reported by patients; * significance at p<0.05.

Table 2 Results of statistical significance as obtained by the Beck Depression Inventory (BDI), Freiburg Questionnaire of Coping with Illness (FQCI) and Stress Coping Inventory (SCI) in patients with B27-AU and an age-matched, healthy control group.

 2

		Patients (P)				p-value for
		vs				gender
		Controls (C) Total	Women	Men	differences
	Numbers	P	171	64	107
		C	55	33	22
	BDI -sum score	P				n.s.
			8.7 (7.0)	9.5 (7.6)	8.4 (6.7)
						n.s

Freiburg Questionnaire of Coping with Illness (FQCI)

Table 3 B27-AU patients' subjective estimations about psychological distress or life events as triggers for relapses Total patient population

 3

	Women	Men

Legend: Data are given as percentage relating to group (total of patients or gender); number of patients per gender group is given in parentheses. * Significance at p<0.05.

Table 4 Previous studies on the psychopathology of uveitis

 4

	Authors	Year	Questionnaires	Number	Uveitis type,	Results
			used (author)	of	number of
				uveitis	patients
				patients
	Schlaegel TF,	1959	Minnesota	49	AU, AU+PU;	Significantly higher
	Levitt EE		multiphasic		granulomatous	values of
			personality		vs. non-	psychopathology in
			inventory		granulomatous;	uveitis patients; the
					severity staging	location, type and
						severity of uveitis or
						sex are not
						correlated with
						psycho-pathology.
	Erbaugh JK,	1962	Personal	71	No details given Uveitis patients
	Fajardo RV		interview			report more
						depressive episodes
						prior to
						hospitalization than
						controls.
	Heaton JM	1964	Personal	224	AU (n=157)	Three potential
			interview		PU (n= 20)	triggers of the
					Pan (n= 47)	disease: 1)
						maladaptation to the
						social environment
						may act as a
						predisposing factor
						because 21% of
						patients mentioned
						interpersonal stress 8
						weeks before uveitis,
						2) influenza in 6.2%,
						3) common cold in
						3.6%.
	Sen DK	1971	Personal	48	AU (n=36)	Stress was reported
			interview		PU (n=5)	as a factor
					Pan (n= 7)	influencing the
						development or
						progression of uveitis
						by 37.5% of patients
						(16.6% reported

Figure 2 Numbers of B27-AU patients stating psychological distress +/- specific life events preceding an acute attack

  Of 171 B27-AU patients, 99 (57.9%) stated to have felt psychological distress before acute relapses, 23.4% only distress, 34.5% distress and specific life events. Women reported a connection more often than men (p=0.045). Distributions within gender group are given in percentages (equal total).

	7,
	p=0.002),

ACKNOWLEDGEMENTS, COMPETING INTERESTS, FUNDING

Acknowledgements: none.

Funding: This work has been partly supported by "Kampf der Blindheit" (Association for Prevention of Blindness) in Vienna. The sponsor was in no way involved in the design or conduct of the research project.

Competing interests: none declared.

COPYRIGHT LICENCE STATEMENT

The corresponding author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd, and its Licensees to permit this article (if accepted) to be published in the British Journal of Ophthalmology and any other BMJPGL products and to exploit all subsidiary rights, as set out in our licence."


Hannah Bartlett
email: h.e.bartlett@aston.ac.uk

Frank Eperjesi

Apparent motion photometry: evaluation and reliability of a novel method for the measurement of macular pigment

Keywords: age-related macular degeneration, apparent motion photometry, macular pigment, macular pigment optical density

Background/aims

Macular pigment (MP) is thought to protect the macula against exposure to light and oxidative stress, both of which may play a role in the development of age-related macular degeneration. Our aim was to clinically evaluate a novel cathode ray tube (CRT) based method for measurement of macular pigment optical density (MPOD) known as apparent motion photometry (AMP).

Methods

We took repeat readings of MPOD centrally (zero degrees) and at three degrees eccentricity for 76 healthy subjects (mean (± SD) 26.5 ± 13.2 years, range 18 to 74 years.

Results

The overall mean MPOD for the cohort was 0.50±0.24 at zero degrees, and 0.28±0.20 at three degrees eccentricity; these values were significantly different (t = -8.905, p < 0.001). The coefficients of repeatability were 0.60 and 0.48 for the zero and three degree measurements respectively.

Conclusions

Our data suggest that when the same operator is taking repeated zero-degree AMP MPOD readings over time, only changes of more than 0.60 units can be classed as clinically significant. In other words, AMP is not suitable for monitoring changes in MPOD over time, as increases of this magnitude would not be expected even in response to dietary modification or nutritional supplementation.

INTRODUCTION

Macular pigment (MP) is thought to protect the most important area of the retina against life-long exposure to light and oxidative stress [START_REF] Loane | The rationale and evidence base for a protective role of macular pigment in age-related maculopathy[END_REF] both of which may play a role in the development of age-related macular degeneration (AMD). [2] the most important cause of low vision in the developed world. [START_REF] Evans | Causes of visual impairment in people aged 75 years and older in Britain: an add-on study to the MRC Trial of Assessment and Management of Older People in the Community[END_REF] Although there are several lines of treatment that offer the possibility of amelioration [START_REF] Landa | Comparative study of intravitreal bevacizumab (Avastin) versus ranibizumab (Leucentis) in the treatment of neovascular age-related macular degeneration[END_REF] the condition is currently incurable. It has been suggested that MP acts as an antioxidant and screener of high-energy blue light. [START_REF] Krinsky | Possible biologic mechanisms for a protective role of xanthophylls[END_REF] Macular pigment may prevent light-initiated oxidative damage to the retina and therefore protect against subsequent age-related macular disease. [START_REF] Hammond | Preservation of visual sensitivity of older individuals: association with macular pigment density[END_REF] Therefore, it is important to develop methods for MP measurement in order to be able to offer advice on increasing MP levels.

Heterochromic flicker photometry (HFP), is a psychophysical technique that has proved popular, [START_REF] Loane | Measurement of macular pigment optical density using two different heterochromic flicker photometers[END_REF] and allows a subject to match the luminance of two differently coloured lights in a test field that flickers between the two by adjusting the luminance of one. When the two lights are equiluminant the flicker is greatly reduced or absent. To measure MPOD, the subject makes a heterochromatic match between a light absorbed by the MP, i.e. blue light, and a light not so absorbed, such as green. The match is made in the fovea where MP levels are high and again at a parafoveal location where it is assumed there is no MP. Comparing the two matches allows the MPOD to be calculated. Unfortunately, HFP has disadvantages such as the fact that it is a conceptually difficult task for subjects, and there is no assessment of fixation, and these have been discussed in detail elsewhere. [START_REF] Mellerio | A portable instrument for measuring macular pigment with central fixation[END_REF][START_REF] Moreland | Macular pigment measurement by apparent motion photometry[END_REF][10]This means that an alternative approach is worth investigating. The aim of this study was to clinically evaluate a novel cathode ray tube (CRT) based method for measurement of MPOD, which is commercially available as part of the Metropsis psychophysical vision test suite (Cambridge Research Systems Ltd., 80 Riverside Estate, Sir Thomas Longley Road, Rochester, Kent ME2 4BH England).

The use of a CRT display driven by sophisticated software offers a way to overcome many of the problems of HFP. The spectral power distribution of the blue phosphor of a CRT matches the absorption spectrum of the MP such that light that is absorbed by MP is generated.The long wavelength light that comes from the red phosphor can be used as the non-absorbed light. Anstis and Cavanagh described an apparent motion technique whereby four square wave gratings, each 90 degree phase advanced from the previous grating, are presented sequentially. [START_REF] Anstis | A minimum motion technique for judging equiluminance[END_REF] The first grating is a chromatic grating composed of alternate red and blue bars. The luminance of the blue is fixed whilst the red luminance can be varied.

The second grating is a purely luminance modulated achromatic grating, modulated around the mean luminance of the blue/red chromatic grating. The sequence of gratings appears to move in one direction or the other, the direction being solely dependent upon the relative subjective luminance of the two components in the chromatic gratings. In this case, when the red luminance is greater the grating appears to drift upwards and when the blue luminance is greater the grating appears to shift downwards. At subjective equiluminance the stimulus appears to pulsate or flicker with no apparent motion, or with some parts moving one way and others moving in the opposite direction. The advantage of this stimulus is that judging the direction of apparent motion is conceptually easy for most naive subjects. We will refer to this method as apparent motion photometry (AMP).

We are currently not aware of any other study that has investigated the repeatability of AMP.

Repeatability is the ability to duplicate measurements obtained by a measuring technique on an intersession basis. [START_REF] Zadnik | The repeatability of measurement of the ocular components[END_REF] Our aim was to determine the inter-session measurement variability, or measurement noise, of AMP in order to be able to identify what a clinically significant change in MPOD would be when using this technique. This is of particular interest since AMP might be used to monitor the effect of nutritional supplementation or dietary modification on MPOD over time.

MATERIALS AND METHODS

Subjects

Seventy-six healthy subjects were recruited from the staff, students and patients of Aston University Optometry department and public service eye clinics. Ethical approval was obtained from the University's Office of Human Research. Written consent was obtained after each participant had been fully informed of the nature of the study according to the code of ethics in the Declaration of Helsinki protocol. None had a history of ocular disease, amblyopia or ocular surgery. All had a visual acuity of at least 0.10 log MAR (approximately 6/7.5 in Snellen notation) in each eye with habitual refractive correction where necessary.

Materials

Stimuli were presented on a calibrated Mitsubishi Diamond Pro 2070SB monitor, viewed at 80 cm, driven by a Metropsis Precision Vision Testing System (Cambridge Research Systems Ltd, Rochester, UK) which has 14 bit luminance video resolution and precision temporal control, guaranteeing stimulus veracity. Each subject's gaze direction was continually measured with a video eye tracker (Cambridge Research Systems Ltd, Rochester, UK).

Protocol

Stimuli were presented on the monitor and viewed at 80 cm. One reference field, and two test fields were used to obtain MPOD readings at zero and three degrees eccentricity from the fovea. The seven degree reference field, assumed to be outside the extent of MP, was taken as baseline reference for MPOD calculation. The zero and three-degree test fields were compared with this reference to obtain an MPOD value at each of those locations. The stimuli presented at three and seven degrees eccentricity were composed of a radial grating in a 90 degree arc concentric to a white fixation cross and with the width and spatial frequency scaled to reduce with reducing eccentricity. The stimulus presented at zero eccentricity (central MPOD) and was composed of horizontal gratings forming a vertical rectangle 0.3 by 1.2 degrees.

The frequency of presentation of the grating sequence was optimised for each subject to maximise the perception of motion. Using a rotary control, each subject was able to vary the presentation rate so as to achieve the strongest motion perception to a typical eccentric stimulus with the luminances of the red and blue components of the chromatics gratings markedly different. In order to saturate the S cones, stimuli were presented on a full field uniform background using only the field blue phosphor at a luminance of 12 cd/m 2 , typically around 300 Trolands. The luminance of the blue component of the chromatic gratings was fixed at 10 cd/m 2 . For each new test field position the red component initially had a luminance of 24 cd/m 2 and was varied by a 2AFC weighted up/down staircase algorithm controlled by the subject pushing a button on a response box to indicate if the movement was up or down. Computer software automatically calculated the MPOD using the following equation: MPOD = log (EfB/EfR) -log (EpB/EpR) where, at subjective equiluminance, EfB is the luminance of the blue chromatic grating component at an eccentricity of f degrees within the macula, EfR the luminance of the red chromatic grating component at an eccentricity of f degrees within the macula, EpB the luminance of the blue chromatic grating component at an eccentricity of 7 degrees and EpR the luminance of the red chromatic grating component at an eccentricity of 7degrees both outside the macula.

When the red luminance was at or near that of the blue, motion ceased or became anomalous. Subjects were instructed to always press the down button unless they were sure the motion was upward. Because the final MPOD value was calculated as a ratio of the luminance values recorded for the foveal and parafoveal locations, asking subjects to adopt this method did not affect the overall result. To obtain convincing apparent motion the mean luminance and contrast of the achromatic grating mimics that of the chromatic grating.

In order to reduce adaptation effects each test field was presented for only 500 msec. Correct fixation is vital if valid MPOD profiles are to be obtained; the subject's head was partly restrained by a chin and head rest and the subject's gaze direction was continually measured with the video eye-tracker. This was used to inhibit stimulus presentation until fixation was correct. Fixation had to be within ±0.5 degrees of the fixation point. If the subject broke fixation during stimulus presentation the stimulus was extinguished and the presentation repeated once correct fixation was re-established. Initially it was found that some subjects could not see coherent motion in any test field and thus could not make measurements of their MPOD. We ascertained that younger subjects required higher stimulus presentation frequencies than older, and the software was changed to allow subjects to optimise as described above all aspects of grating presentation before a series of measurements was commenced. Generally, subjects under 40 years found sequence presentation frequencies in the range of 15 to 20 Hz satisfactory whilst subjects older than 40 years chose lower frequencies but the frequency chosen was not very critical. Once the grating parameters had been optimised, subjects found the procedure easy and most naive subjects could complete a MP profile with readings at each test field in less than 10 minutes. Data were collected by one operator (HB) in two sessions separated by one week. Prior to the first session a trial run was completed, to allow each participant to practice the test. Practice run data were not included in the analysis. The study design permitted assessment of the test repeatability (HB1 versus HB2).

Data analysis and display

Microsoft Windows XP and SPSS software was used for data analysis. Graphs were produced using Sigma Plot software (version 6) for Microsoft Windows XP.

RESULTS

We measured MPOD for 76 healthy subjects (mean (± SD) 26.5 ± 13.2 years, range 18 to 74 years). Our sample consisted of 26 males and 50 females. The overall mean central MPOD for the cohort was 0.50 ± 0.24, calculated by averaging the mean of the two central readings for each subject. The overall mean MPOD at three degrees eccentricity was calculated in the same way, and was 0.28 ± 0.20. The zero and three degree MPOD values were significantly different (t = -8.905, p < 0.001). There was no correlation between AMP central MPOD readings and age (r = -0.051, p = 0.665) or between three-degree MPOD readings and age (r = 0.105, p = 0.367). The mean central MPOD reading for females (n = 50) was 0.53 ± 0.25 and for males (n = 26) was 0.44 ± 0.21; there was no significant gender difference (t = 0.-1.719, p = 0.090). The mean three degree MPOD reading for females was 0.29 ± 0.21 and for males was 0.27 ± 0.18, and again, there was no significant gender difference (t = -0.327, p = 0.745). There was significant positive correlation between the first and second readings for zero degree (r = 0.419, p < 0.001) and three-degree (r = 0.487, p < 0.001) data sets.

Analysis of inter-session repeatability involved calculating the difference in the MPOD for each subject obtained by one observer between two test sessions. The degree of inter-session repeatability is the range over which 95% of the differences lie i.e. the 95% limits of repeatability are equal to the mean difference ±1.96 x standard deviation of the differences. [START_REF] Bland | Statistical methods for assessing agreement between two methods of clinical measurement[END_REF] The limits of repeatability are shown in table 1 and were also plotted as the difference versus the mean of the MPOD in the two test sessions (see

DISCUSSION

We have measured MPOD on 76 healthy subjects using a CRT based AMP technique that has adopted the apparent motion of the grating phenomenon described by Anstis and Cavanagh. [START_REF] Anstis | A minimum motion technique for judging equiluminance[END_REF] The coefficient of repeatability values indicate the amount of change that can occur between readings and still be classed as instrument 'noise'. Our data suggests that when the same operator is taking repeated zero-degree AMP MPOD readings over time, only increases or decreases of more than 0.60 units can be classed as clinically significant (see figure 1), and when the same operator is taking repeated three-degree AMP MPOD readings over time, only increases or decreases in MPOD of more than 0.48 units can be classed as clinically significant (see figure 2).

The coefficient of repeatability for the central MPOD reading was 0.60. This is comparable with the results a similar studies that have assessed the repeatability and reproducibility of the Macuscope™ macular pigment densitometer, which uses the psychophysical method of HFP to measure MPOD, One study found a coefficient of repeatability of 0.58 for this instrument, [START_REF] Bartlett | Clinical evaluation of the MacuScope TM macular pigment densitometer[END_REF] and another reported coefficients of variance of 36.1% and 23% for right and left eyes respectively. [START_REF] Hagen | Repeated measures of macular pigment optical density to test reproducibility of heterochromatic flicker photometry[END_REF] The mean central MPOD value was 0.50 ± 0. ). [START_REF] Hagen | Repeated measures of macular pigment optical density to test reproducibility of heterochromatic flicker photometry[END_REF]The wide range of mean MPOD values may be the result of differing test protocols and stimulus characteristics.

We also report a three-degree MPOD value of 0.28 ± 0.20, which was significantly lower than the central value (t = -8.0.5, p < 0.001). This decline with eccentricity supports work on primate monkeys using microspectrophotometry that found a peak in MPOD at the fovea with a sharp decline towards four degrees of eccentricity, [21 22] as well as a high-performance liquid chromatography study on donor eyes that reported negligible levels of MPOD at seven degrees eccentricity. [START_REF] Bone | Analysis of the macular pigment by HPLC: retinal distribution and age study[END_REF] There has been considerable interest in determining how far from the fovea the MPOD falls to negligible levels because in psychophysical measurements of MPOD the luminance of the light absorbed by MP at each eccentricity is compared against a baseline luminance from a match made in a part of the retina that is assumed to have no MPOD. Some workers have used a point at four degrees eccentricity as this reference, [START_REF] Hammond | Macular pigment optical density in a Southwestern sample[END_REF] but MPOD profiles have been reported where measurable pigment extends to five, six, seven degrees or even further. [START_REF] Robson | Macular pigment density and distribution: comparison of fundus autofluorescence with minimum motion photometry[END_REF] There now seems to be a consensus that seven to eight degrees is a reasonable eccentricity to choose for the baseline [START_REF] Moreland | Macular pigment measurement by apparent motion photometry[END_REF] and this is easily achieved with the display used in this study.

We also found that the optimum frequency for a coherent motion illusion chosen by subjects could vary quite widely from day-to-day and that there was a trend for this frequency to deccrease with age. For our subjects there was no significant correlation between frequency and age but the majority of subjects (93%) were under the age of 40 years. For some subjects the range of luminances over which anomalous motion was reported varied. We countered this issue by instructing the subject to respond down unless they perceived clear upwards motion and consider this to be a valid strategy in determining a reversal point in the staircase procedure.

In conclusion, our results suggest that if central MPOD is being monitored over time to assess the effect of an intervention, then any change less than 0.60 units should not be considered clinically significant as they are very likely to be due to measurement noise. In other words, AMP is not suitable for monitoring changes in MPOD over time, as increases of this magnitude would not be expected even in response to dietary modification or nutritional supplementation.

Heterochromatic flicker photometry (HFP) has been used in research environments to assess macular pigment optical density (MPOD), and this psychophysical technique is considered to be the gold standard for macular pigment measurement despite the fact that it is a conceptually difficult task for patients to perform. This study is the first to independently evaluate the alternative apparent motion photometry technique for MPOD measurement, which is commercially available as part of the Metropsis psychophysical vision test suite (Cambridge Research Systems Ltd., 80 Riverside Estate, Sir Thomas Longley Road, Rochester, Kent ME2 4BH England), and is thought to be a conceptually more accessible task. The coefficient of repeatability for the central (zero-degree) measurement is 0.60, which compares well with our reported coefficient of repeatability for the Macuscope™, which is 0.58. This information is important for practitioners who may be using the Metropsis suite to assess the longitudinal effect of nutritional supplementation or dietary modification on MPOD.

COPYRIGHT LICENCE STATEMENT

The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd, and its Licensees to permit this article (if accepted) to be published in British

Journal of Ophthalmology and any other BMJPGL products and to exploit all subsidiary rights, as set out in our licence

AUTHORSHIP

Both named authors were involved in the conception and design of the study, analysis and interpretation of data, and revising it critically for important intellectual content. Both named authors gave final approval of the version published. HB collected the data. HB and FE drafted the final manuscript.

Figure 1 :

 1 Figure 1: Difference in zero-degree MPOD reading between sessions one and two, compared with the

Figure 2 :

 2 Figure 2: Difference in three-degree MPOD reading between sessions one and two, compared with the

Table 1 :

 1 Coefficient of repeatability for the zero and three-degree apparent motion photometry derived

	figures 1 and 2).

  24. Other studies that used HFP to measure MPOD have

	reported average values in normal cohorts of 0.211 ± 0.13 (n= 280, age range: 18-50 years),[16] 0.28 ±
	0.21 (n= 280, age range: 18-50 years),[17] 0.289 ± 0.156 (n = 46, age range: 21-81 years),[18] 0.319 (n =
	100, age range: 22-60 years),[19], 0.43 ± 0.23 (n = 1648, age range: 53-86 years),[20] 0.47 ± 0.14 (n =
	38, age range: 19-46 years),[14] and from 0.58 ± 0.29 to 0.72 ± 0.27 (n = 24, mean age: 38.1 ± 10.6
	years

ACKNOWLEDGEMENTS

Cambridge Research Systems provided the equipment used in this study. Hannah Bartlett was funded by a grant from the Macular Disease Society. The authors declare no conflict of interest.

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC

Heterochromic flicker photometry has been used to assess MPOD in the clinical and research environments, but is a conceptually difficult task. Our group has found coefficient of repeatability values of 0.58 for the Macuscope™, and 0.33 for the MPS 9000, which are both commercially available instruments. The AMP technique for MPOD measurement is thought to be an easier task, and so this study has been designed to assess its repeatability.

WHAT THIS STUDY ADDS


Stefano Ferrari

Diego Ponzin

Jane L Ashworth

Kristina Teär Fahnehjelm

C Gail Summers

Paul R Harmatz

Maurizio Scarpa
email: scarpa@pediatria.unipd.it

Diagnosis and management of ophthalmologic features in patients with mucopolysaccharidosis

Keywords: Diagnosis, Eye Diseases, Glycosaminoglycans, Mucopolysaccharidoses, Treatment pathology, imaging, diagnostic tests/investigation, treatment medical, child health (paediatrics)

SUMMARY

Ocular pathology is common in patients with mucopolysaccharidosis (MPS), an hereditary lysosomal storage disorder, where the eye as well as other tissues accumulate excessive amounts of glycosaminoglycans. Despite genetic and phenotypic heterogeneity within and between different types of MPS, the disease symptoms and clinical signs often manifest during the first six months of life with increasing head size, recurrent infections, umbilical hernia, growth retardation and skeletal problems. Typical ocular features include corneal clouding, ocular hypertension/glaucoma, retinal degeneration and optic nerve atrophy. Visual deterioration and sensitivity to light may substantially reduce the quality of life in MPS patients, particularly when left untreated.

As an early intervention, haematopoietic stem cell transplantation and/or enzyme replacement therapy are likely to improve patients' symptoms and survival, as well as visual outcome.

Thus, it is of utmost importance to ensure proper detection and accurate diagnosis of MPS at an early age. Fundamental herein is to increase awareness and knowledge among ophthalmologists of the ocular problems affecting MPS patients and to highlight potential diagnostic pitfalls and difficulties in patient care.

This review provides insight into the prevalence and severity of ocular features in patients with MPS and gives guidance for early diagnosis and follow-up of MPS patients. MPS poses therapeutic challenges in ocular management, which places ophthalmologists next to paediatricians at the forefront of interventions to prevent long-term sequelae of this rare but serious disease.

The clinical features of mucopolysaccharidoses

The mucopolysaccharidoses (MPS) are a heterogeneous group of lysosomal storage disorders that are genetically inherited in an autosomal recessive manner (except for MPS II which is X-linked). [START_REF] Wraith | The mucopolysaccharidoses: a clinical review and guide to management[END_REF] These inborn metabolic diseases are characterised by functional defects in particular lysosomal enzymes, involved in the breakdown of glycosaminoglycans (GAGs, acid mucopolysaccharides) (Table 1). [START_REF] Wraith | The mucopolysaccharidoses: a clinical review and guide to management[END_REF] Depending on the type of MPS, the resulting catabolic error causes progressive accumulation of particular GAGs in lysosomes and their abnormally high excretion in urine (Table 1). [START_REF] Wraith | The mucopolysaccharidoses: a clinical review and guide to management[END_REF] Histochemical examinations have demonstrated cytoplasmic membrane-bound vacuoles containing GAGs in almost all ocular tissues of MPS patients. [START_REF] Kenyon | Ocular manifestations and pathology of systemic mucopolysaccharidoses[END_REF][START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] These deposits alter the cellular shape and tissue ultrastructure, resulting in progressive physiological dysfunction that presents clinically at a young age and ultimately can cause visual impairment or blindness. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] Accumulation of GAGs in other organs are the cause of typical coarse facial features, skeletal deformities (e.g., dysostosis multiplex), growth retardation (often accelerated in the first 12-18 months), cardiac valvular abnormalities, respiratory difficulties and gastrointestinal problems (e.g., hepatosplenomegaly, bowel dysfunction) as well as intellectual and behavioural impairment (in the severe forms of MPS I, II and III) (fig 1). [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] About 70% of patients have central nervous system involvement, albeit to different extents. Ocular manifestations vary and include corneal clouding, ocular hypertension/glaucoma, retinal degeneration and optic nerve swelling with subsequent atrophy. The severity and relative predominance of the ocular features, depend on the MPS (sub)type (Table 1). [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] Nevertheless, phenotypic variation is often observed, [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] which is likely due to the mutational heterogeneity of the enzyme involved, [START_REF] Karageorgos | Mutational analysis of 105 mucopolysaccharidosis type VI patients[END_REF][START_REF] Beesley | Mutational analysis of 85 mucopolysaccharidosis type I families: frequency of known mutations, identification of 17 novel mutations and in vitro expression of missense mutations[END_REF] that may lead to absent or attenuated enzyme activity. [START_REF] Karageorgos | Mutational analysis of 105 mucopolysaccharidosis type VI patients[END_REF][START_REF] Müller-Forell | Mucopolysaccharidoses (MPS). Clinical and neuroradiological aspects of the different types[END_REF] Further mutational analysis studies may reveal potential genotype-phenotype correlations.

Call for early detection and diagnosis of MPS

Early detection allows prompt intervention of this devastating disorder in a primary stage with haematopoietic stem cell transplantation (HSCT) and/or enzyme replacement therapy (ERT) and thus, better prognosis and outcomes for the patient. While a rapid colorimetric screening of the urinary GAG expression level is quite predictive, [START_REF] Müller-Forell | Mucopolysaccharidoses (MPS). Clinical and neuroradiological aspects of the different types[END_REF][START_REF] De Jong | Measuring urinary glycosaminoglycans in the presence of protein: an improved screening procedure for mucopolysaccharidoses based on dimethylmethylene blue[END_REF] the definitive diagnosis is mostly based upon a combination of clinical, radiological and laboratory (e.g., specific lysosomal enzyme activity assay) methods from collaborative medical specialties. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Müller-Forell | Mucopolysaccharidoses (MPS). Clinical and neuroradiological aspects of the different types[END_REF] Given its phenotypic heterogeneity and its rarity, with an overall cumulative incidence rate of 2 to 5 patients with MPS out of 100,000 live births, [START_REF] Baehner | Cumulative incidence rates of the mucopolysaccharidoses in Germany[END_REF][START_REF] Lin | Incidence of the mucopolysaccharidoses in Taiwan, 1984-2004[END_REF] Although paediatricians often encounter and recognise patients with MPS, patients with the attenuated form (e.g., MPS I S that present at later ages -older than 5 years) may be first seen and diagnosed by ophthalmologists because of the eye involvement. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] Patients less than 5 years old with a severe form (MPS I H) have been described, who were not diagnosed until glaucoma developed. [START_REF] Nowaczyk | Glaucoma as an early complication of Hurler's disease[END_REF] These findings highlight the crucial role of ophthalmologists in contributing to early detection of MPS in children.

Ocular problems in MPS

Anterior segment

Corneal clouding can involve all layers of the cornea including the epithelium, stroma and endothelium. Structural alterations caused by GAG deposition, including an abnormal cell shape and irregular collagen fibril diameter, spacing and arrangement in the stroma, result in reduced transparency and increased light scattering. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Alroy | Altered corneal stromal matrix organization is associated with mucopolysaccharidosis I, III and VI[END_REF] Corneal clouding varies from being subtle to severe and is often described as being of ground glass appearance. It typically has a diffuse pattern, [START_REF] Kenyon | Ocular manifestations and pathology of systemic mucopolysaccharidoses[END_REF] although primarily peripheral corneal clouding has been described in MPS I S. [START_REF] Summers | Dense peripheral corneal clouding in Scheie syndrome[END_REF] A moderately positive correlation between corneal clouding and central corneal thickness has been reported, [START_REF] Connell | Central corneal thickness and its relationship to intraocular pressure in mucopolysaccararidoses-1 following bone marrow transplantation[END_REF] although this has not been corroborated by others. [START_REF] Summers | Ocular changes in the mucopolysaccharidoses after bone marrow transplantation. A preliminary report[END_REF] Progressive corneal clouding is a prominent feature of patients with MPS I, VI and VII (Table 1, fig 2). [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] It may first be asymptomatic and then present as photophobia associated with slowly progressive loss of visual acuity. [START_REF] Martins | Guidelines for the management of mucopolysaccharidosis type I[END_REF] Signs and symptoms reported from the MPS I Registry revealed that corneal clouding is common, being present in over 80% of the patients, regardless of age at onset. [START_REF] Pastores | The MPS I registry: design, methodology, and early findings of a global disease registry for monitoring patients with mucopolysaccharidosis type I[END_REF] All 19 patients with MPS VI in a Brazilian study showed corneal clouding that ranged from mild to severe. [START_REF] Azevedo | Clinical and biochemical study of 28 patients with mucopolysaccharidosis type VI[END_REF] This high prevalence of corneal clouding in MPS was further confirmed by a retrospective case series, which found that MPS VI patients were more severely affected than MPS I patients (Table 2). [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] In addition to corneal clouding, peripheral vascularisation of the cornea may also be present in MPS patients. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF] This can occur following chronic corneal oedema due to raised intraocular pressure (IOP), or secondary to corneal exposure associated with pseudo-exophthalmos (fig 2)

and/or post-treatment graft-versus-host disease. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] Both superficial and deep vessels were observed in all four cases with glaucoma in association of MPS VI. [START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF] Open-angle [START_REF] Nowaczyk | Glaucoma as an early complication of Hurler's disease[END_REF][START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF][START_REF] Spellacy | Glaucoma in a case of Hurler disease[END_REF] and acute/chronic angle-closure glaucoma [START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF][START_REF] Quigley | Acute glaucoma in systemic mucopolysaccharidosis I-S[END_REF][START_REF] Mullaney | Glaucoma in mucopolysaccharidosis 1-H/S[END_REF] have both been observed in MPS patients (Table 1). GAG accumulation and the consequent thickening of the cornea can lead to narrowing of the anterior chamber angle, and deposition within trabecular cells may cause obstruction of outflow. [START_REF] Nowaczyk | Glaucoma as an early complication of Hurler's disease[END_REF][START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF] Another potential cause of angle closure and subsequent increased IOP is the development of multiple iridociliary cysts. [START_REF] Sato | Multiple iridociliary cysts in patients with mucopolysaccharidoses[END_REF] The prevalence of glaucoma is estimated at 10% for the MPS I population. [START_REF] Pastores | The MPS I registry: design, methodology, and early findings of a global disease registry for monitoring patients with mucopolysaccharidosis type I[END_REF] While ocular hypertension and glaucoma are fairly rare in other types of MPS, elevated IOP was observed in approximately half of the patients with MPS VI (Table 2) and could be due to their corneal changes because a statistically significant relationship between IOP and corneal clouding has been found. [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] This illustrates the difficulty in distinguishing increased corneal rigidity and thickness from true raised IOP and potential glaucoma. Only one patient with MPS VI, however, had an enlarged cup-to-disc ratio. [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] Posterior segment

Ultrasound examinations in 65 patients with MPS have demonstrated significantly thicker sclera at the posterior pole and a widened optic nerve and its sheath. [START_REF] Schumacher | Sonographic ocular findings in patients with mucopolysaccharidoses I, II and VI[END_REF] These morphological changes probably develop very early in the course of the disease. [START_REF] Schumacher | Sonographic ocular findings in patients with mucopolysaccharidoses I, II and VI[END_REF] Thickened sclera may subsequently lead to vortex vein obstruction and development of the uveal effusion syndrome as described in one patient with MPS II. [START_REF] Vine | Uveal effusion in Hunter's syndrome. Evidence that abnormal sclera is responsible for the uveal effusion syndrome[END_REF] Optic disc and optic nerve pathologies are present in MPS (Table 1). Optic disc swelling of mild-to-moderate severity was noted in 50% of the patients with MPS VI, while optic nerve atrophy in 2 of 14 cases. [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] Similar rates for MPS VI were observed in a study by Collins et al, while optic nerve atrophy was slightly more common in MPS I H and I H/S patients (Table 2). [START_REF] Collins | Optic nerve head swelling and optic atrophy in the systemic mucopolysaccharidoses[END_REF] Optic disc swelling (i.e., papilloedema) and subsequent optic nerve atrophy can occur secondary to high intracranial pressure (ICP) [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF], or follow nerve compression due to GAGthickened dura and sclera. [START_REF] Giugliani | Management guidelines for mucopolysaccharidosis VI[END_REF] Alternative causes of optic nerve atrophy may be the degeneration of optic nerve ganglion cells due to intracellular GAG deposition or optic disc cupping and atrophy due to increased IOP. [START_REF] Giugliani | Management guidelines for mucopolysaccharidosis VI[END_REF] Retinopathy occurs as a result of GAG deposition within retinal pigment epithelial (RPE) cells and in the inter-photoreceptor matrix, leading to progressive photoreceptor loss, retinal degeneration and dysfunction (fig 2). [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] This may clinically appear as sensitivity to light, central or peripheral vision loss, clumsiness, night blindness, etc., [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] and display an identical histopathology to retinitis pigmentosa. [START_REF] Kenyon | Ocular manifestations and pathology of systemic mucopolysaccharidoses[END_REF] Variable degrees of retinopathy, with associated changes in the electroretinogram (ERG), have predominantly been seen in MPS I, II and III (Table 1, Table 2). [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF][START_REF] Caruso | Electroretinographic findings in the mucopolysaccharidoses[END_REF] ERG evidence of retinal dysfunction ranged from none to severe for MPS I and II patients, while all MPS III patients demonstrated moderately-to-severely affected ERGs. [START_REF] Caruso | Electroretinographic findings in the mucopolysaccharidoses[END_REF] The ERG findings were similar to those seen in primary and secondary rod-cone retinal degeneration, where the depression of rod-mediated responses exceeds that of the cone system, [START_REF] Summers | Ocular changes in the mucopolysaccharidoses after bone marrow transplantation. A preliminary report[END_REF][START_REF] Caruso | Electroretinographic findings in the mucopolysaccharidoses[END_REF][START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF] causing a reduction in b-waves on dark adaptation. [START_REF] Tzetzi | Negative ERGs in mucopolysaccharidoses (MPS) Hurler-Scheie (I-H/S) and Hurler (I-H)-syndromes[END_REF] In several cases, ophthalmological signs and symptoms did not correlate with the electrophysiological findings; funduscopic findings were restricted to only mild changes of the RPE or vascular attenuation. [START_REF] Caruso | Electroretinographic findings in the mucopolysaccharidoses[END_REF] Thus, as in any other disease, ophthalmological examination is not sufficient to rule out retinal involvement in MPS. [START_REF] Caruso | Electroretinographic findings in the mucopolysaccharidoses[END_REF] Lastly, macular oedema and maculopathy has been reported in MPS I S and MPS II. [START_REF] Anawis | Hunter syndrome (MPS II-B): a report of bilateral vitreous floaters and maculopathy[END_REF][START_REF] Usui | Macular edema-like change and pseudopapilledema in a case of Scheie syndrome[END_REF] Best-corrected visual acuity (BCVA) differs in patients with MPS. Whereas a BCVA of at least 0.5 in more than half (58%) of the Swedish MPS I patients was found (Fahnehjelm KT et al, accepted by Acta Ophthalmol 2010), other reports demonstrated a high rate of visual impairment in patients with MPS I (Table 2). [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF][START_REF] Connell | Central corneal thickness and its relationship to intraocular pressure in mucopolysaccararidoses-1 following bone marrow transplantation[END_REF] This distinction could be caused by phenotypic variations, variable age at examination or diagnosis, and consequent compliance with correction of the high hypermetropia or treatment of amblyopia. Also patients with MPS VI can suffer from visual impairment (Table 2). [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] In addition, patients with both MPS VI and MPS I have been reported with amblyopia, ranging between 32 and 44% of the patients, and strabismus, ranging between 25 and 44%. [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] Refractive errors are also common in patients with MPS. The majority (> 90%) of patients with MPS I (of either sub-type) and MPS VI for whom refraction data were available had hypermetropia. [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF][START_REF] Fahnehjelm | Ocular findings in four children with mucopolysaccharidosis I-Hurler (MPS I-H) treated early with haematopoietic stem cell transplantation[END_REF][START_REF] Pitz | Ocular changes in patients with mucopolysaccharidosis I receiving enzyme replacement therapy: a 4-year experience[END_REF][START_REF] Pitz | Does enzyme replacement therapy influence the ocular changes in type VI mucopolysaccharidosis?[END_REF] It has been speculated that hypermetropia is caused by GAG-mediated increased rigidity of the cornea, thereby straightening its curvature and reducing its refractive power. [START_REF] Fahnehjelm | Ocular findings in four children with mucopolysaccharidosis I-Hurler (MPS I-H) treated early with haematopoietic stem cell transplantation[END_REF] Hypermetropia could also result from scleral thickening and shortened axial length (Fahnehjelm KT et al, accepted by Acta Ophthalmol 2010).

Assessment and diagnosis of eye disorders in MPS

An accurate diagnosis of the ocular manifestations in MPS patients may be a challenge because of poor cooperation of the patient and due to the different underlying ocular and other pathologies. [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] Severe photophobia may hamper clinical examination in general, [START_REF] Fahnehjelm | Ocular findings in four children with mucopolysaccharidosis I-Hurler (MPS I-H) treated early with haematopoietic stem cell transplantation[END_REF] while the corneal involvement in MPS may make diagnosis of glaucoma difficult.

Firstly, thickening and increased corneal rigidity can falsely elevate the IOP values. [START_REF] Connell | Central corneal thickness and its relationship to intraocular pressure in mucopolysaccararidoses-1 following bone marrow transplantation[END_REF][START_REF] Tonnu | The influence of central corneal thickness and age on intraocular pressure measured by pneumotonometry, non-contact tonometry, the Tono-Pen XL, and Goldmann applanation tonometry[END_REF] This effect on IOP validity is more observed in non-contact tonometry than in Goldman applanation tonometry. [START_REF] Tonnu | The influence of central corneal thickness and age on intraocular pressure measured by pneumotonometry, non-contact tonometry, the Tono-Pen XL, and Goldmann applanation tonometry[END_REF] In that sense, dynamic contour tonometry that uses the principle of corneal contour matching instead of applanation may be more reliable and suitable for patients with MPS. [START_REF] Francis | Effects of corneal thickness, corneal curvature, and intraocular pressure level on Goldmann applanation tonometry and dynamic contour tonometry[END_REF] Given its possible impact on IOP, it is certainly worthwhile to assess the corneal thickness by pachymetry. [START_REF] Lanzl | Ocular features of treatable lysosomal storage disorders -Fabry disease, mucopolysaccharidoses I, II and VI and Gaucher disease[END_REF] Secondly, another frequently encountered difficulty when assessing glaucoma is related to corneal clouding, which hampers a clear view by ophthalmoscopy and gonioscopy, limiting the assessment of optic disc cupping (i.e., cup-to-disc ratio) and visualisation of the drainage angle. [START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF][START_REF] Quigley | Acute glaucoma in systemic mucopolysaccharidosis I-S[END_REF] Similarly, corneal clouding can also lead to difficulties in diagnosing and monitoring papilloedema, optic nerve atrophy and retinal or macular degeneration by funduscopic examination after dilatation or by optical coherence tomography that can distinguish the different retinal layers. [START_REF] Yoon | High-speed, ultrahigh resolution optical coherence tomography of the retina in Hunter syndrome[END_REF] Therefore, ultrasound examination may be a valuable and suitable alternative to obtain better image quality in patients with MPS. In intercellular spaces in all corneal layers and microdeposits of 1.0 to 3.8 µm outside and inside stromal keratocytes that appear rounded with clearly demarcated hyporeflective regions are characteristic features found in MPS I and MPS VI patients. [START_REF] Grupcheva | In vivo microstructural analysis of the cornea in Scheie's syndrome[END_REF][START_REF] Mocan | In vivo confocal microscopic findings of two siblings with Maroteaux-Lamy syndrome[END_REF][START_REF] Patel | In vivo microstructural analysis of the cornea in Maroteaux-Lamy syndrome[END_REF] In addition, the diagnostic assessment of ocular pathologies is frequently complicated by the patients' physical inabilities, young age and developmental delay (behavioural or intellectual disabilities), particularly when cooperation is needed for visual field measurements. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] Sometimes, an ERG examination under sedation or anaesthesia to determine severity of retinopathy can be helpful. General anaesthesia, however, can be dangerous in patients with MPS due to co-existent cardiovascular or respiratory problems (severe oro-pharyngeal and upper airway narrowing) [START_REF] Belani | Children with mucopolysaccharidosis: perioperative care, morbidity, mortality, and new findings[END_REF]. This leads to problems with intubation and pre-/post-operative complications, [START_REF] Belani | Children with mucopolysaccharidosis: perioperative care, morbidity, mortality, and new findings[END_REF][START_REF] Walker | Anaesthesia and mucopolysaccharidoses. A review of airway problems in children[END_REF][START_REF] Sjøgren | Mucopolysaccharidoses and anaesthetic risks[END_REF], requiring an experienced anaesthesiologist (for children with MPS). [START_REF] Diaz | Perioperative management of children with mucopolysaccharidoses[END_REF]. Retinoscopy is also hampered in the anaesthetised child as the correct axis can only be approximated, which can be a major source of error. Therefore, simple clinical tests (e.g., colour vision Hardy Rand Rittler and Cone Adaptation Test) can be used in the office for initial screening of retinal pathology. Upon suspicion of retinal pathology, ERG under general anaesthesia may be considered.

Recording of visual evoked potentials (VEPs) is more easily performed. In patients with severe corneal clouding, flash VEPs show a decreased signal, while optic nerve pathologies due to increased ICP may reflect in attenuated amplitudes or delayed latencies of the VEPs.

However, it is worth noting that normal VEPs may be found in patients with swollen optic discs in early (not chronic) stages.

International expert panels have recommended that MPS patients are evaluated on a regular basis for their ophthalmic problems, i.e., at least every 12 months for MPS I and MPS VI, and according to the individual patient's needs as determined by the treating physician. [START_REF] Pastores | The MPS I registry: design, methodology, and early findings of a global disease registry for monitoring patients with mucopolysaccharidosis type I[END_REF][START_REF] Giugliani | Management guidelines for mucopolysaccharidosis VI[END_REF].

Revision final, 07-06-2010 14

Apart from more specific investigations such as pachymetry, ultrasound examination and electrophysiology when needed, basic clinical follow-ups in children with MPS should include evaluation by an orthoptist to detect strabismus, evaluation of IOP, retinoscopy after cycloplegia to detect high refractive errors, and evaluation of the fundi, including photography in the cooperative patient.

Therapeutic approaches in MPS and its ocular features

Integrated medical care necessitates a multi-disciplinary expert approach in the treatment of patients with MPS. [START_REF] Wraith | The mucopolysaccharidoses: a clinical review and guide to management[END_REF][START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] Input from different paediatric sub-specialties, including ophthalmology, is important and needs to consider the risk-benefit balance of treatment. [START_REF] Wraith | The mucopolysaccharidoses: a clinical review and guide to management[END_REF] Because many patients with MPS are at increased anaesthetic risk, [START_REF] Walker | Anaesthesia and mucopolysaccharidoses. A review of airway problems in children[END_REF][START_REF] Sjøgren | Mucopolysaccharidoses and anaesthetic risks[END_REF] local anaesthesia is often preferable, though age and mental status are relative deterrents, [START_REF] Sjøgren | Mucopolysaccharidoses and anaesthetic risks[END_REF] and any procedure with sedation must be performed in a specific referral centre.

Ocular therapies in MPS

The predominance of corneal clouding, glaucoma and concomitant visual deterioration in MPS necessitates thorough clinical examinations, prescription of optimal correction and if needed, corneal transplantation and glaucoma treatment. To correct corneal clouding, penetrating keratoplasty (PK) (fig 3) or, more advanced techniques such as lamellar keratoplasty, are valuable treatment options in the absence of retinal degeneration (Pinello L et al, submitted to Clin Exp Ophthalmol). Deep anterior lamellar keratoplasty is currently favoured over conventional PK in MPS patients because of similar effectiveness and lower risks. [START_REF] Nischal | Pediatric keratoplasty[END_REF] Although no systematic studies on the outcome of keratoplasty in patients with MPS have been performed, good results with the maintenance of clear donor cornea for a period of 3 months up to 5 years (without systemic therapies) were obtained in various cases. [START_REF] Bergwerk | Corneal transplantation in a patient with mucopolysaccharidosis type VII (Sly disease)[END_REF][START_REF] Käsmann-Kellner | Ocular changes in mucopolysaccharidosis IV A (Morquio A syndrome) and long-term results of perforating keratoplasty[END_REF][START_REF] Varssano | Corneal transplantation in Maroteaux-Lamy syndrome[END_REF][START_REF] Uçakhan | Long-term follow-up of corneal graft survival following bone marrow transplantation in the Maroteaux-Lamy syndrome[END_REF][START_REF] Rosen | Five year maintenance of corneal graft normality in systemic mucopolysaccharidosis[END_REF] However, while clearing of the host cornea has been noted, [START_REF] Naumann | Clearing of cornea after perforating keratoplasty in mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome)[END_REF] GAGs may reaccumulate in the grafted tissue. [START_REF] Käsmann-Kellner | Ocular changes in mucopolysaccharidosis IV A (Morquio A syndrome) and long-term results of perforating keratoplasty[END_REF][START_REF] Schwartz | Occurrence of mucopolysaccharide in corneal grafts in the Maroteaux-Lamy syndrome[END_REF] Re-opacification, as early as one year postsurgery [START_REF] Käsmann-Kellner | Ocular changes in mucopolysaccharidosis IV A (Morquio A syndrome) and long-term results of perforating keratoplasty[END_REF][START_REF] Schwartz | Occurrence of mucopolysaccharide in corneal grafts in the Maroteaux-Lamy syndrome[END_REF], likely correlates with disease severity [START_REF] Käsmann-Kellner | Ocular changes in mucopolysaccharidosis IV A (Morquio A syndrome) and long-term results of perforating keratoplasty[END_REF] and could be attributable to anterior-posterior spread of host keratocytes and gradual replacement of epithelial cells by host epithelium. [START_REF] Schwartz | Occurrence of mucopolysaccharide in corneal grafts in the Maroteaux-Lamy syndrome[END_REF] In addition, concomitant retinal degeneration, optic nerve atrophy, glaucoma or other dysfunctions may limit the success of PK in terms of visual improvement (fig 3). [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Käsmann-Kellner | Ocular changes in mucopolysaccharidosis IV A (Morquio A syndrome) and long-term results of perforating keratoplasty[END_REF] Therefore, the potential benefits to vision and quality of life, even if temporary, must be weighed against co-existent eye pathologies, anaesthetic risks, intensive postoperative care and risk of complications in patients with MPS. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] When glaucoma is suspected -bearing influencing factors in mind and taking diagnostic difficulties into account -balancing the pros and cons of anti-glaucoma therapy [START_REF] Schwartz | Current management of glaucoma[END_REF] is similarly important. Clinical reports of anti-glaucoma therapy in patients with MPS are scarce and relatively dated. [START_REF] Nowaczyk | Glaucoma as an early complication of Hurler's disease[END_REF][START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF][START_REF] Spellacy | Glaucoma in a case of Hurler disease[END_REF][START_REF] Quigley | Acute glaucoma in systemic mucopolysaccharidosis I-S[END_REF][START_REF] Mullaney | Glaucoma in mucopolysaccharidosis 1-H/S[END_REF][START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF] This finding highlights the rarity of the MPS disorder and the difficulty in identifying glaucoma in MPS patients, because co-existent corneal clouding frequently hampers gonioscopy and ophthalmoscopy and because visual fields are usually not obtained. [START_REF] Cantor | Glaucoma in the Maroteaux-Lamy syndrome[END_REF][START_REF] Quigley | Acute glaucoma in systemic mucopolysaccharidosis I-S[END_REF] Systemic therapies in MPS Disease-specific systemic therapies, i.e., HSCT and ERT, re-establish the regular GAG catabolism in the body. With the aim to reverse, arrest or at least slow down disease progression and considerably improve the patients' outcome and quality of life, [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF] it is advantageous to start treatment early in life (i.e., HSCT before 24 months of age and ERT shortly after birth). [START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF][START_REF] Pitz | Ocular changes in patients with mucopolysaccharidosis I receiving enzyme replacement therapy: a 4-year experience[END_REF][START_REF] Pitz | Does enzyme replacement therapy influence the ocular changes in type VI mucopolysaccharidosis?[END_REF][START_REF] Harmatz | Entering a new treatment age for mucopolysaccharidosis VI disease: a search for better markers of disease progression and response to treatment[END_REF][START_REF] Muenzer | Mucopolysaccharidosis I: management and treatment guidelines[END_REF][START_REF] Gabrielli | Enzyme-replacement therapy in a 5-month-old boy with attenuated presymptomatic MPS I: 5-year follow-up[END_REF][START_REF] Mcgill | Enzyme replacement therapy for mucopolysaccharidosis VI from 8 weeks of age -a sibling control study[END_REF] Such necessitates early diagnosis.

HSCT encompasses the transplantation of matched healthy donor cells (from bone marrow or umbilical cord blood) and has achieved beneficial effects on ocular problems, although not uniformly or in the long term. [START_REF] Summers | Ocular changes in the mucopolysaccharidoses after bone marrow transplantation. A preliminary report[END_REF][START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF][START_REF] Fahnehjelm | Ocular findings in four children with mucopolysaccharidosis I-Hurler (MPS I-H) treated early with haematopoietic stem cell transplantation[END_REF] Indeed, HSCT has been reported to reduce but not fully eliminate corneal clouding, [START_REF] Summers | Ocular changes in the mucopolysaccharidoses after bone marrow transplantation. A preliminary report[END_REF][START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF][START_REF] Fahnehjelm | Ocular findings in four children with mucopolysaccharidosis I-Hurler (MPS I-H) treated early with haematopoietic stem cell transplantation[END_REF] to resolve optic nerve oedema [START_REF] Summers | Ocular changes in the mucopolysaccharidoses after bone marrow transplantation. A preliminary report[END_REF][START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF], and to improve ERG results. [START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF] (Summers CG et al, submitted to Clin Exp Ophthalmol) However, retinal degeneration can progress despite engraftment [START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF] and visual function may remain compromised. [START_REF] Fahnehjelm | Ocular findings in four children with mucopolysaccharidosis I-Hurler (MPS I-H) treated early with haematopoietic stem cell transplantation[END_REF] (Summers CG et al, submitted to Clin Exp Ophthalmol) HSCT requires a suitable donor and there is significant risk of post-transplantation systemic morbidity and mortality (e.g., infection, graft-versus-host-disease, rejection and complications from adjuvant radiation or chemotherapy). [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Giugliani | Management guidelines for mucopolysaccharidosis VI[END_REF] In addition, ocular complications may arise following HSCT, e.g., cataracts secondary to corticosteroid therapy and irradiation, keratoconjunctivitis sicca and post-intervention retinopathy. [START_REF] Ashworth | Mucopolysaccharidoses and the eye[END_REF][START_REF] Gullingsrud | Ocular abnormalities in the mucopolysaccharidoses after bone marrow transplantation. Longer follow-up[END_REF][START_REF] Fahnehjelm | Dry-eye syndrome after allogeneic stemcell transplantation in children[END_REF][START_REF] Fahnehjelm | Visual outcome and cataract development after allogeneic stem-cell transplantation in children[END_REF] As an alternative to HSCT, ERT has been developed and recommended in patients because of its favourable safety profile. [START_REF] Giugliani | Management guidelines for mucopolysaccharidosis VI[END_REF] ERT is also used before HSCT to improve the patient's respiratory function and somatic status. [START_REF] Cox-Brinkman | Haematopoietic cell transplantation (HCT) in combination with enzyme replacement therapy (ERT) in patients with Hurler syndrome[END_REF][START_REF] Wynn | Use of enzyme replacement therapy (Laronidase) before hematopoietic stem cell transplantation for mucopolysaccharidosis I: experience in 18 patients[END_REF] The administration of purified recombinant enzyme via regular intravenous infusion is now approved for the Hurler/Hurler-Scheie MPS I syndrome (laronidase), [64] MPS II (idursulfase) [START_REF]Elaprase ®[END_REF] and MPS VI (galsulfase). [START_REF] Naglazyme | [END_REF] Clinically meaningful and sustained improvements in functional capacity and other systemic signs have been observed with ERT in phase III studies. [START_REF] Harmatz | Enzyme replacement therapy for mucopolysaccharidosis VI: a phase 3, randomized, double-blind, placebo-controlled, multinational study of recombinant human N-acetylgalactosamine 4-sulfatase (recombinant human arylsulfatase B or rhASB) and follow-on, open-label extension study[END_REF][START_REF] Harmatz | Long-term follow-up of endurance and safety outcomes during enzyme replacement therapy for mucopolysaccharidosis VI: final results of three clinical studies of recombinant human N-acetylgalactosamine 4sulfatase[END_REF][START_REF] Scarpa | Mucopolysaccharidosis VI: the Italian experience[END_REF][START_REF] Muenzer | A phase II/III clinical study of enzyme replacement therapy with idursulfase in mucopolysaccharidosis II (Hunter syndrome)[END_REF][START_REF] Clarke | Long-term efficacy and safety of laronidase in the treatment of mucopolysaccharidosis I[END_REF][START_REF] Wraith | Enzyme replacement therapy for mucopolysaccharidosis I: a randomized, double-blinded, placebo-controlled, multinational study of recombinant human α-L-iduronidase (laronidase)[END_REF] With respect to ocular manifestations, stability or improvement of corneal clouding and visual acuity was apparently found in some patients, but controversy about other ocular pathologies such as optic disc changes remains. [START_REF] Pitz | Ocular changes in patients with mucopolysaccharidosis I receiving enzyme replacement therapy: a 4-year experience[END_REF][START_REF] Pitz | Does enzyme replacement therapy influence the ocular changes in type VI mucopolysaccharidosis?[END_REF][START_REF] Scarpa | Mucopolysaccharidosis VI: the Italian experience[END_REF][START_REF] Clarke | Long-term efficacy and safety of laronidase in the treatment of mucopolysaccharidosis I[END_REF][START_REF] Wraith | The first 5 years of clinical experience with laronidase enzyme replacement therapy for mucopolysaccharidosis I[END_REF][START_REF] Kakkis | Enzyme-replacement therapy in mucopolysaccharidosis I[END_REF][START_REF] Koseoglu | Reversed papilledema in an MPS VI patient with galsulfase (Naglazyme ® ) therapy[END_REF] (Summers CG et al, submitted to Clin Exp Ophthalmol) More assessments are necessary to provide a clear-cut picture of the effects of ERT, and its combination with HSCT, on the course of ocular changes. [START_REF] Ashworth | The ocular features of the mucopolysaccharidoses[END_REF] Limitations of ERT include the risk of allergic or immune reactions related to the administration route (successfully managed by antihistamines and a slower infusion rate), infections associated with regular administration, as well as penetration problems at particular 'privileged sites'. [START_REF] Giugliani | Management guidelines for mucopolysaccharidosis VI[END_REF] The enzyme, at the doses currently administered, does not cross the blood-brain barrier and presumably, likewise, not the blood-retina barrier to an appreciable extent. [START_REF] Pitz | Does enzyme replacement therapy influence the ocular changes in type VI mucopolysaccharidosis?[END_REF] need to take into account the compromised health condition of MPS patients when balancing the benefits and risks of procedures such as corneal transplantation or glaucoma treatment.

Systemic therapies that re-establish GAG breakdown (such as HSCT or ERT) could bring relief as part of integrated care, although more investigations are warranted, particularly with regard to their effectiveness on ocular abnormalities in MPS.

  than 6/12 Snellen equivalent in the better eye # values relate to eyes, not patients ERG: electroretinogram; NA: not available; +: mild; ++: moderate; +++: severe

Figure 1 .Figure 2 .Figure 3 .

 123 Figure 1. Patients with MPS VI of varying severity [copyright BioMarin Inc]

Table 1 .

 1 Classification of different MPS types according to enzyme deficiency and with indication of the severity of ocular pathologies (slightly adapted from Ashworth et al.[3]*) Note that there are inter-patient variations

	MPS type (eponym)	Enzyme deficiency	Involved GAG		Eye diseases
				Corneal clouding	Glaucoma	Retinopathy	Optic nerve abnormalities
	MPS I H (Hurler)	α-L-iduronidase	DS, HS	+++	++	++	++
	MPS I H/S (Hurler-Scheie)	α-L-iduronidase	DS, HS	++	++	++	++
	MPS I S (Scheie)	α-L-iduronidase	DS, HS	+	+	++	+
	MPS II (Hunter)	iduronate-2-sulfatase	DS, HS	+	+	++	++
		heparan sulfamidase (A)
		N-acetyl-α-D-glucosaminidase (B)
	MPS III (Sanfilippo) A-B-C-D	acetyl-CoA-α-glucosaminidase	HS	+	+	+++	+
		N-acetyltransferase (C)
		N-acetylglucosamine-6-sulfatase (D)
	MPS IV A (Morquio A)	N-acetylgalactosamine-6-sulfatase	KS	+	+	++	+
	MPS VI (Maroteaux-Lamy)	N-acetylgalactosamine-4-sulfatase	DS	+++	++	unknown	++
	MPS VII (Sly)	β-D-glucuronidase	DS, HS, CS	++	unknown	unknown	++
	MPS IX (Natowicz)	hyaluronidase	CS	unknown	unknown	unknown	unknown
	+: mild; ++: moderate; +++: severe; CS: chondroitin sulfate; DS: dermatan sulfate; GAG: glycosaminoglycan; HS: heparan sulfate; KS: keratan sulfate

Table 2 .

 2 Prevalence of ocular features in patients with MPS I and VI (expressed as % of affected patients unless indicated otherwise)

	MPS type	Corneal	Ocular	Optic disc	Optic atrophy[26] # Retinopathy[4]	Visual impairment
		clouding[4]	hypertension	swelling[26] #		(<20/40*)[4]
		+; ++; +++	(> 21 mm Hg)[4]
	MPS I H	N = 19	N = 19
		47%; 37%; 16%

  The multi-organ involvement and rarity of MPS hamper early recognition of this disease. The diagnosis is often delayed while precious time is spent on expert-to-expert referral.Ophthalmologists can play a crucial role in diagnosing MPS because they encounter patients with corneal clouding and other ocular problems at a relatively early age, and must be informed regarding the various manifestations in MPS.(Ashworth JL et al, accepted by Clin Exp Ophthalmol) Diagnosing ocular pathologies can be a challenging task due to concomitant influencing factors (e.g., corneal clouding hampering viewing techniques and corneal thickening with a risk of elevating IOP values) or because the patients' physical or mental incapacities reduce cooperation.(Ashworth JL et al, accepted by Clin Exp Ophthalmol) Similarly, ocular therapies

	CONCLUDING REMARKS

Consequently, the ocular involvement in MPS may require novel therapeutic strategies or tailored drug delivery routes, in order to ensure substantial concentrations and sufficient pharmacological effects. Promising attempts in MPS animal models include, amongst others, systemic gene therapy and local injections in the eye.[76,77] (Ponder KP et al, submitted to Clin Exp Ophthalmol) Results of recent phase I clinical trials in patients with Leber congenital amaurosis[78-80] bode well for local gene therapy in (posterior) eye complications associated with other well-defined, single-gene disorders such as MPS. Future interventions with gene therapy will likely change the outcomes of individuals affected with MPS, but early diagnosis will be required for maximum benefit.

ACKNOWLEDGEMENTS

The authors are grateful to Ismar Healthcare NV for their writing assistance, which was funded by BioMarin Europe Ltd, London, UK.

The content of the manuscript is based on presentations and discussions during a scientific meeting entitled 'MPS and The Eye', which took place from 7-9 October 2009 in Venice, Italy. The authors would like to thank the other faculty members for their contribution during this meeting, including Prof. A. Auricchio, Dr. B. Bachmann, Prof. M. Busin, Prof. H.S. Dua, Dr. L. Fontana, Prof. R. Giugliani, Prof. J.V. Jester, Dr. G.K. Klintworth, Prof. K. Landau, Mr. A.M. Lobo, Prof. Y. Omidi, Prof. G. Palù, Dr. S. Pitz, Prof. K.P. Ponder, Dr. A. Suppiej, Prof. A.P. Tormene and Dr. C.E. Willoughby. This meeting was supported by an educational grant from BioMarin Europe Ltd, London, UK. BioMarin had no role in the content presented and discussed at the meeting. All authors participated in the development and writing of the manuscript and are fully responsible for its content. BioMarin reviewed the manuscript with respect to the accuracy of statements concerning ERT for MPS VI.

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