PhD Marta Gonzalez-Hernandez

MD Luis E Pablo

Karintia Armas-Domingue

Ricardo Rodriguez

La Vega

MD Antonio Ferreras
email: aferreras@msn.com

Manuel Gonzalez De La

Karintia Armas-Dominguez

MD Ricardo Rodriguez De La Vega Bsc

MD Manuel Gonzalez De La Rosa

Structure-function relationship depends on glaucoma severity

Keywords: Visual field, perimetry, glaucoma, optic nerve head, HRT, papilla

teaching and research institutions in France or abroad, or from public or private research centers.

Introduction

Morphologic deterioration is generally considered to precede functional alterations in glaucoma, but it depends on the methods or diagnostic criteria used to evaluate this topic. In a previous report, [START_REF] Gonzalez De La Rosa | Optic disc tomography and perimetry in controls, glaucoma suspects, and early and established glaucomas[END_REF] we presented theoretical objections to this idea based on our clinical observations that certain morphologic indices obtained using the Heidelberg Retina Tomograph (HRT II) are highly correlated with the mean sensitivity (MS) of standard white-on-white automated perimetry (SAP), such that the expected error in deducing the SAP-MS from the morphologic parameters is less than 2 decibels (dB) in the first phases of the disease. New perimetric procedures have been added to the diagnostic arsenal for glaucoma; e.g., new strategies to reduce retinal neurologic fatigue, such as tendency oriented perimetry (TOP) [START_REF] Gonzalez De La Rosa | Accuracy of the Tendency Oriented Perimetry (TOP) in the Octopus 1-2-3 Perimeter[END_REF] or the Swedish interactive threshold algorithm (SITA), [START_REF] Bengtsson | A new generation of algorithms for computerized threshold perimetry, SITA[END_REF] or procedures that examine functions other than differential light threshold, such as high resolution perimetry, [START_REF] Frisen | High pass resolution targets in peripheral vision[END_REF] short-wavelength automated perimetry, [START_REF] Hart | Glaucomatous visual field damage. Luminance and color-contrast sensitivities[END_REF] or frequency-doubling perimetry, [START_REF] Maddess | Clinical trials of the frequency doubled illution as an indicator of glaucoma[END_REF] which have sought to analyse the parvo-, konio-, and magnocellular pathways to confirm or provide an earlier diagnosis. [START_REF] Ferreras | Can frequency-doubling technology and shortwavelength automated perimetries detect visual field defects before standard automated perimetry in patients with pre-perimetric glaucoma?[END_REF][START_REF] Fogagnolo | Short-wavelength automated perimetry and frequency-doubling technology perimetry in glaucoma[END_REF] There is no absolute certainty, however, that some of these nerve pathways are selectively affected early in glaucoma. [START_REF] Harwerth | Visual field defects and neural losses from experimental glaucoma[END_REF] Moreover, recent studies have cast doubt on previous affirmations that the perimetries used to estimate some of these specific visual functions are valuable for the diagnosis of early glaucoma. [START_REF] North | Evaluation of the high specificity Screening Program (C-20-1) of the Frequency Doubling Technology (FDT) perimeter in clinical practice[END_REF][START_REF] Bengtsson | Diagnostic sensitivity of fast blue-yellow and standard automated perimetry in early glaucoma: a comparison between different test programs[END_REF] It has been argued that functional analysis procedures for diagnosing glaucoma inevitably lead to a late diagnosis, because of the logarithmic nature of the progression of glaucoma due to the concentration of residual ganglion cells. The relationship between morphology and function, however, may be linear rather than logarithmic at early stages of the disease. Although function is immediately lost with neuronal death, the thickness of the retinal nerve fibre layer (RNFL) is not immediately impacted. 12 ,13 Thus, the relationship between the concentration of residual ganglion cells and morphologic measurements may not be linear, but rather curvilinear. If both morphology and function are measured by non-linear scales, however, the relationship between them might be approximately linear. For example, if a newborn animal doubles its weight and height every day, the growth is not linear with respect to time although the relationship between weight and height is linear. Moreover, morphologic measurements of the optic nerve head (ONH) and its surroundings do not take into account functional eccentricity. Recent histopathologic studies in monkeys trained for perimetric research indicate that the slope of perimetry in relation to ganglion cell count varies with the eccentricity of the region being investigated. [START_REF] Harwerth | Scaling the structure--function relationship for clinical perimetry[END_REF] In the present study, we compared the linear and logarithmic relationship between changes in morphology and function in a sample comprising healthy subjects, glaucoma suspects, and glaucoma patients.

Methods

This study was conducted in accordance with the tenets of the Declaration of Helsinki. The ethics committee of our hospital approved the study and informed consent was obtained from each subject.

Subjects and measurement protocol

The study comprised 1235 eyes from 1235 subjects: 228 controls, 766 glaucoma suspects, and 241 glaucoma patients. All participants were required to have a best-corrected visual acuity better than 0.8 (Snellen), refractive error within ±5.00 diopters equivalent sphere and ±2.00 diopters astigmatism, transparent ocular media, and an open anterior chamber angle. Subjects with any eye disease other than glaucoma, taking medication that could affect visual field performance, a pupil diameter <3 mm, or perimetric catch trials outside the normal range (>33%) were excluded.

All subjects underwent a full ophthalmologic examination that included a family or personal history related to glaucoma, such as migraine, Raynaud Syndrome, arterial hypo-and hypertension, diabetes, cardiovascular disease, smoking, and medication; refraction and visual acuity; anterior segment examination and gonioscopy; Goldmann applanation tonometry; ONH topography performed with the HRT II (Heidelberg Engineering, Dossenheim, Germany); and SAP (tendency oriented perimetry TOP strategy and "32" grid) using the Octopus 311 perimeter (HAAG-STREIT, Bern, Switzerland). The visual field tests were performed with a distance refractive correction for SAP. For all participants, including normal subjects, the results of the first two visual field examinations were ignored to minimize the learning effect. Posterior pole examination under mydriasis was also performed using a slit-lamp with a bi-convex lens (Volk 78 diopters).

Sample groups

The control group comprised subjects with no general disease or treatment that could affect vision, no family history of glaucoma, intraocular pressure (IOP) less than 21 mmHg, normal ONH appearance, and no other sign or symptom associated with glaucoma (e.g., migraine, Raynaud Syndrome, vasculopathy, etc.). Glaucoma suspects were consecutively recruited in our specialized hospital clinic, referred from several outpatient clinics. Referral was based mainly on IOP levels (> 21 mmHg), or family history of glaucoma.

Glaucoma patients attending a periodic examination at our hospital were consecutively selected. All of them had an IOP higher than 21 mmHg and glaucomatous ONH morphology.

Glaucomatous damage was defined as focal or diffuse neuroretinal rim narrowing with concentric enlargement of the optic cup, localized notching, or both. [START_REF] Tuulonen | Initial glaucomatous optic disk and retinal nerve fiber layer abnormalities and their progression[END_REF] One eye from each subject was randomly chosen, unless only one eye met the inclusion criteria.

The division of the sample into groups was made following standard criteria commonly used in glaucoma studies. The purpose of the statistical procedure was to determine the best structurefunction relationship throughout the different stages of the disease, and therefore the whole sample was used in the statistical analyses.

Statistical analyses

All statistical analyses were performed with Statistica 6.0 software (Tulsa, OK). The association between perimetric and anatomic indices was calculated using a simple linear and logarithmic regression (mean sensitivity [MS] = a + b x log 10 [morphologic index]), where "a" is the constant and "b" the regression equation slope. Linear regression is used to analyse the relationship between two variables in order to find the best straight line through the data. The goal of linear regression analysis is to adjust the values of the slope and intercept to find the line that best predicts y from x.

We performed a linear analysis of morphology with respect to the luminance (L) of the threshold stimulus (SAP-L) and the inverse function (SAP-1/L). The relationship between the visual field threshold values, which are indicated in dB, and the light intensity (L) is represented on a logarithmic scale. The relationship depends on the maximum intensity (Lmax) of the stimulus at the perimeter. Thus, retinal sensitivity (dB) = -10 x log (L/Lmax). The white stimulus presented by the Octopus perimeter varied in intensity from 0.00 to 4800 apostilbs (asb). Thus, a 0 dB value corresponds to the maximum brightness that the perimeter can produce (i.e., a stimulus intensity of 4800 asb). The patient's sensitivity at each point is expressed on a dB scale of light attenuation (1 dB = 0.1 log unit). For example, a point with 31 dB sensitivity indicates that the maximum 4800-asb white stimulus was attenuated by 31 dB (or 3.1 log units) to reach the threshold value of detection. For that reason, the analysis was performed with linear scale SAP-MS values, e.g. SAP-L and SAP-1/L. Pearson's correlation coefficient and the standard error of estimation (SEE) were calculated between the SAP-MS and global mean RNFL thickness based on HRT. The SEE is the error produced when using morphologic values to predict functional values and vice versa; hence, it is an estimation of the dissociation between the morphologic and functional values.

Piecewise linear regression was used to analyse whether a single regression line or two separate regression lines best fit the data. Piecewise regression compares regressions developed from possibly different populations to identify a possible breakpoint.

Results

The normal group consisted of 228 eyes of 228 healthy individuals (mean age 55.6 ± 16.2 years). The mean SAP-MS was 26.5 ± 1.6 dB (coefficient of variation=6.19%) and the mean HRT II-global mean RNFL thickness was 0.26 mm ± 0.07 (coefficient of variation=29.27%).

The patient group (patients with glaucoma or suspected glaucoma) included 1007 eyes of 1007 patients (mean age 57.6 ± 15.7 years). The mean SAP-MS was 21.6 ± 6.6 dB and mean defect (MD) was 4.9 ± 6.3 dB.

For the whole sample (normals, patients with suspected glaucoma, and glaucoma patients), the logarithmic relationship between SAP-MS and mean RNFL thickness (r=0.487, SSE=5.54 dB) was not better than the linear relationship (r=0.487, SEE=5.54 dB; p=0.992; Figure 1). The linear adjustment of the mean RNFL thickness with respect to SAP-L (r=0.293) was significantly weaker than that with respect to SAP-MS (p<0.001). SAP-1/L (r=0.428) was no stronger than SAP-MS (p=0.06).

Piecewise linear regression identified a breakpoint with SAP-MS=22.42 dB, thereby splitting the whole sample into two different populations with significantly different regression slopes (p<0.05). In 825 cases, SAP-MS was over 22.42 dB; 227 belonged to the control group and 598 to the patient group. The logarithmic relationship between SAP-MS and mean RNFL thickness (r=0.182, SSE=1.80 dB) was not different from the linear relationship (r=0.185, SEE=1.80 dB; p=0.950; Figure 2). The linear adjustment of RNFL with respect to SAP-L (r=0.190) and SAP-1/L (r=0.169) was also not significantly different from that with respect to SAP-MS (p=0.916 and p=0.738, respectively).

In 410 cases, SAP-MS was under 22.42 dB; only 1 of these cases belonged to the control group. In these 410 cases, the logarithmic relationship between SAP-MS and mean RNFL thickness (r=0.353, SSE=5.80 dB) was not significantly different from the linear relationship (r=0.344, SEE= 5.83 dB; p=0.884; Figure 3). The linear adjustment of mean RNFL thickness with respect to SAP-L (r=0.235) or SAP-1/L (r=0.331) was also not significantly different from that with respect to SAP-MS (p=0.089 and p=0.834, respectively).

Figure 4 shows the original and linear regression-estimated values for both populations divided by the obtained breakpoint (SAP-MS=22.42 dB). Basically the first population (cases with SAP-MS>22.42 dB) included controls, patients with suspected glaucoma, and those with early glaucoma. In these cases, function can be accurately estimated using morphologic parameters (mean RNFL thickness was 0.24 mm [SD=0.09], which was slightly lower than that in control subjects [0.26 mm; SD=0.07; p=0.048]). The group that included subjects with more advanced glaucoma (SAP-MS <22.42 dB) presented with a larger gap between the morphologic and functional parameters; mean RNFL thickness was significantly lower (0.15 mm; SD=0.10; p<0.001; Figure 5).

Discussion

The non-linear relationship between the GDx and perimetric visual threshold was initially established by Garcia-Sanchez and Garcia-Feijoo (Garcia-Sanchez J, Garcia-Feijoo J.

Relationship between the RNFL thickness and the visual field using nonlinear regression models.

European Glaucoma Society Meeting [EGS]. London. June 2000)

. The linear nature of the data obtained by currently available procedures for measuring morphology in relation to the concentration of residual ganglion cells, however, is only a hypothesis that has not yet been verified.

If the morphologic indices that we study in clinical practice are linear with respect to the number of residual ganglion cells, one would expect that their relation with visual threshold, which is expressed logarithmically in dB, would also be logarithmic. [START_REF] Garway-Heath | Mapping the visual field to the optic disc in normal tension glaucoma eyes[END_REF][START_REF] Garway-Heath | Scaling the hill of vision: the physiological relationship between light sensitivity and ganglion cell numbers[END_REF][START_REF] Reus | The relationship between standard automated perimetry and GDx VCC measurements[END_REF][START_REF] Ferreras | Mapping standard automated perimetry to the peripapillary retinal nerve fiber layer in glaucoma[END_REF] This would imply that a logarithmic relationship should be found in any region of the retina, and for any stage of the disease. Nevertheless, this curvilinear relationship does not seem to exist in normal subjects with differing functional capacity, and is only observed in certain specific regions of the glaucomatous retina. In other regions, such as the nasal and papillary temporal regions, there is no clear relationship between the morphologic alterations and functional changes. [START_REF] Reus | Relationships between standard automated perimetry, HRT confocal scanning laser ophthalmoscopy, and GDx VCC scanning laser polarimetry[END_REF][START_REF] Horn | Association between localized visual field losses and thickness deviation of the nerve fiber layer in glaucoma[END_REF] This curvilinear, possibly logarithmic, relationship has been described in studies analyzing glaucomatous patients for the whole range of the disease, as we have verified in the global analysis of our population. In other studies of patients with fewer moderate and severe defects, the logarithmic relationship is less evident. [START_REF] Bowd | Structure-function relationships using confocal scanning laser ophthalmoscopy, optical coherence tomography, and scanning laser polarimetry[END_REF] When the analysis is restricted to normal subjects and patients in the first stages of the disease, or selectively to those with moderate or severe defects, there is no evidence that the relation is logarithmic.

In individuals with severe defects, although there is a minimal significant correlation, the variability of the data is very high, making it impossible to differentiate between advanced and absolute glaucoma, [START_REF] Tsai | Scanning laser polarimetry for measurement of retinal nerve fiber layer in absolute, advanced and early glaucoma[END_REF] and the correlation between morphology and function disappears. [START_REF] Blumenthal | Correlating structure with function in endstage glaucoma[END_REF] Based on our results, the curvilinear relationship between morphology and function is not due to the linearity of anatomic measurements by the instruments we used with respect to the concentration of residual ganglion cells. Such a relationship is not demonstrated when the analysis is performed independently for the initial and advanced stages of glaucoma. We believe that this apparent curvilinear relation is due to the lack of a dynamic range in the procedures for detecting morphologic changes in advanced glaucoma. The relationship is essentially linear at early stages of the disease, although the excessive interindividual morphologic variability reduces the slope of the relationship.

With regard to the relationship between morphologic and functional indices in normal subjects, patients with suspected glaucoma, and those with mild glaucoma (SAP-MS <22.42 dB, Figure 3), the distribution of points suggests that great morphologic changes are accompanied by small functional changes. This finding confirms the idea of delayed decreased function with respect to anatomic change, [START_REF] Reus | The relationship between standard automated perimetry and GDx VCC measurements[END_REF] and may result from interindividual variability of the morphologic parameters, which is far greater than the functional variability.

The findings of the present study verified that interindividual variability in the mean RNFL thickness measured with the HRT II was more than four times greater than that in SAP-MS in normal subjects. Moreover, the variability in SAP-MS may be further reduced by correcting for age, whereas RNFL loss in association with neuronal loss with ageing has not been so clearly demonstrated. [START_REF] Gonzalez De La Rosa | Optic disc tomography and perimetry in controls, glaucoma suspects, and early and established glaucomas[END_REF] We conclude that in patients with very mild or no functional glaucomatous damage, the morphologic values are also proximal to normal. In a general way it is, therefore, not possible to determine with an acceptable precision the degree of functional damage based on the structural data. Note that in patients with suspected glaucoma and early glaucoma patients the mean RNFL thickness was comparable to that in normal subjects.

Figure 1 :

 1 Figure 1: Scatter plot between global mean retinal nerve fibre layer (RNFL) thickness measured

Figure 2 :

 2 Figure 2: Scatter plot between mean retinal nerve fibre layer (RNFL) thickness measured with

Figure 3 :

 3 Figure 3: Scatter plot between mean retinal nerve fibre layer (RNFL) thickness measured with

Figure 4 :

 4 Figure 4: Scatter plot between predicted and observed standard automated perimetry mean

Figure 5 :

 5 Figure 5: Mean retinal nerve fibre layer (RNFL) thickness frequency distribution for individuals

Acknowledgments:

We would like to acknowledge the guidance of Mr. Alejandro Jimenez Sosa (Methodological Consultant).

Licence for Publication

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 to permit this article (if accepted) to be published in BJO and any other BMJ Group products and to exploit all subsidiary rights, as set out in our licence (http://bjo.bmj.com/ifora/licence.pdf).


Eca Macdonald

P A Cauchi

A Azuara-Blanco

B Foot

Surveillance of Severe Chemical Corneal Injuries in the UK

Keywords: Eye Injury, Chemical Corneal Injuries, Conjunctival Injuries, Alkali Injuries, Limbal Stem Cell Deficiency, Surveillance

Aim

To estimate the incidence of severe chemical corneal injuries in the United Kingdom and describe presenting clinical features and initial management.

Methods

All patients with severe chemical corneal injury in the UK from December 2005 to November 2006 inclusive were prospectively identified using the British Ophthalmological Surveillance Unit. Reporting ophthalmologists provided information regarding presentation and follow up.

Results

Twelve cases were identified, giving a minimum estimated incidence in the UK of severe chemical corneal injury of 0.02 per 100 000. 66.7% of injuries were in males of working age, 50% occurred at work, alkali was causative in 66.7%.

Only one patient was wearing eye protection at the time of injury, 75% received immediate irrigation. Six patients required 1 or more surgical procedures; most commonly amniotic membrane graft. At 6 months follow-up best corrected visual acuity was 6/12 or better in five patients, and worse than 6/60 in two.

Conclusion

The incidence of severe chemical corneal injury in the UK is low. The cases that occur can require extended hospital treatment, with substantial ocular morbidity and visual sequelae. Current enforcement of eye protection in the workplace in the UK has probabaly contributed to a reduced incidence of severe ocular burns.

INTRODUCTION

Chemical injuries to the eye represent an ophthalmic emergency that can result in extensive damage with significant ocular morbidity. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF] Most are mild and accidental and do not result in lasting ocular morbidity. Severe chemical eye injuries are rare, but can cause significant visual impairment. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF] The extent of ocular injury depends on many factors, including the strength of the chemical agent, duration of exposure, concentration, volume and penetration of the solution. [START_REF] Pfister | Alkali-injuries of the eye[END_REF][START_REF] Arffa | Grayson's diseases of the Cornea[END_REF] Severe chemical injury to the cornea is usually secondary to strongly acidic and alkaline substances. [START_REF] Kuckelkorn | Emergency treatment of chemical and thermal eye burns[END_REF] Alkali injuries more commonly cause significant damage. [START_REF] Kuckelkorn | Emergency treatment of chemical and thermal eye burns[END_REF] Epidemiological data shows severe chemical eye injuries are more common in males, particularly those aged between 16 and 45 yrs. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF][START_REF] Morgan | Chemical burns of the eye: causes and management[END_REF][START_REF] Kuckelkorn | Chemical and thermal eye burns in the residential area of RWTH Aachen. Analysis of accidents in one year using a new automated documentation of findings[END_REF][START_REF] Davis | Topical steroid use in the treatment of ocular alkali burns[END_REF] Most happen accidentally at work or at home, or deliberately from assault. [START_REF] Kuckelkorn | Emergency treatment of chemical and thermal eye burns[END_REF] Various classification scales exist to grade the severity of ocular chemical injuries. The Hughes classification, modified by Ballen and Roper-Hall, recognised the relationship between initial appearance and prognosis. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF] Subsequent classification schemes have been developed, but the Hughes-Roper-Hall classification remains simple and popular. [START_REF] Dua | A new classification of ocular surface burns[END_REF][START_REF] Harun | Modification of classification of ocular chemical injuries[END_REF] In the acute stage it describes the clinical signs and severity in 4 grades. Grade 1 injuries show corneal epithelial damage, with no limbal ischaemia and a clear cornea.

Grade 2 injuries show less than a third of limbal ischaemia and a hazy cornea through which iris details can be seen. Grade 3 involves total loss of corneal epithelium, stromal haze obscuring iris details, and ischaemia between one third and one half of the limbus. Grade 4 injuries represent an opaque cornea and ischaemia of more than half of the limbus. Grades 3 and 4 are recognised as severe. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF] Acute chemical eye injury treated immediately with expedient irrigation and removal of trapped debris is associated with a significantly better visual outcome. [START_REF] Kuckelkorn | Emergency treatment of chemical and thermal eye burns[END_REF] Early management endeavors to preserve the globe integrity by healing of the ocular surface. Treatment is aimed at promoting ocular surface epithelial recovery, augmenting corneal repair, minimising ulceration and controlling the inflammatory response. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF] Surgery may be necessary in the acute setting if healing of the ocular surface is inadequate. In the chronic stages, features of limbal stem cell deficiency can manifest. [START_REF] Dua | Limbal stem cells of the corneal epthelium[END_REF] Long-term management aims to restore the visual function by preserving tear production, managing limbal stem cell deficiency and addressing associated complications such as lid malposition, cataract and glaucoma. [START_REF] Dua | Limbal stem cells of the corneal epthelium[END_REF][START_REF] Azuara-Blanco | Amniotic membrane transplantation for ocular surface reconstruction[END_REF][START_REF] Chiou | Management of conjunctival cicatrizing diseases and severe ocular surface dysfunction[END_REF] The UK national incidence of severe chemical corneal injuries is unclear. Two previous studies in UK centers have reported eight severe chemical corneal injuries presenting to a large teaching hospital over a four year period and none to a district general hospital over a year. [START_REF] Morgan | Chemical burns of the eye: causes and management[END_REF][START_REF] Davis | Topical steroid use in the treatment of ocular alkali burns[END_REF] Based on this limited evidence we anticipated a maximum of 200-300 cases annually in the UK.

This study aimed to estimate the true incidence of severe chemical corneal injuries with a UK wide prospective survey. In addition it aimed to outline the presentation and management of these cases.

METHODS

This was a prospective population-based study performed in association with

the British Ophthalmological Surveillance Unit (BOSU) monthly reporting system as previously described. [START_REF] Foot | The British Ophthalmological Surveillance Unit: an evaluation of the first 3 years[END_REF][START_REF] Imrie | Surveillance of intraocular foreign bodies in the UK[END_REF] All ophthalmologists with clinical autonomy in the UK receive a monthly reporting card with definitions of the conditions currently under surveillance. They indicate how many new cases of each disorder they have seen or confirm they have seen no new cases. For the 12-month study period December 2005 to November 2006 inclusive, ophthalmologists were asked to report any case of severe chemical corneal injuries presenting to them. This was defined as any person sustaining a injury with all of the following: Every ophthalmologist who notified a patient to the BOSU was sent an initial questionnaire requesting information regarding demographics, aetiology, protective eyewear worn, presenting features and initial management. A 6 month follow-up questionnaire was also sent to ascertain subsequent management and outcome. Ophthalmologists who did not return a questionnaire were sent a reminder letter.

Multi-Centre Research Ethics approval was obtained (REC reference number 05/SO801/111).

RESULTS

Reports to BOSU leading to estimates of the UK incidence of severe chemical corneal injury.

During the study period the BOSU used a reporting base of 1100 ophthalmologists. Each month a mean of 78% of these ophthalmologists provided surveillance information (range 75% -81%). From December 2005 to November 2006 inclusive BOSU received 37 reports of patients with severe chemical corneal injury from 26 ophthalmology consultants. Initial questionnaires were received from 31/ 37 reports (83.8% response rate). Of these 19 were excluded (9 did not meet the inclusion criteria, 5 occurred outwith the study period, 2 were reporting errors and 3 were duplicate cases). Initial questionnaire data was therefore received in 12 true reported cases within the study period. Follow up questionnaires were returned in 10/ 12 (83.3%) cases.

The current UK population is estimated to be approximately 60 million [START_REF]The UK Statistic Authority[END_REF] . The reported annual incidence of severe chemical corneal injury is therefore estimated by this study at 12 per 60 million or 0.02 per 100 000. Eight of the cases occurred in males of working age (16-65yrs), for whom the current UK population estimate is 20 million [START_REF]The UK Statistic Authority[END_REF] . From this study the estimated incidence of severe chemical corneal injury in this group is therefore 8 per 20 million or 0.04 per 100 000.

Patient characteristics and presenting details

Initial details received on the 12 patients showed nine were male (75%). The mean age at time of injury was 33.8 yrs (median 38.5yrs, range 10-59 yrs).

Eight were males of working age, 66.7%. The injury occurred during paid employment in six cases (50%), following assault in 4 (33.3%) and during another activity in two. One patient had a bilateral injury. The causative chemical was reported as alkaline in 8 (66.7%), acidic in 2 (16.7%), other in one and unknown in one. A liquid splash was the mechanism of injury in eight (66.7%), debris was causative in three (25%), there was one reported injury from a gas substance. One patient was wearing goggles at the time of injury, 11 (91.7%) were wearing no eye protection (including prescription spectacles).

The time from injury to first irrigation was less than 1hr in 9 (75%) cases. One case was irrigated at 1-3hrs and one at greater than 12 hrs after the injury (the time to irrigation remained unknown in one patient). Review by an ophthalmologist occurred in two (16.7%) patients within 1 hour of the injury, in five (41.7%) cases between 1-3 hrs and in two eyes at 3-12hrs. Initial review by an ophthalmologist was greater than 12 hrs after the injury in two cases and unknown in one patient. Nine (75%) had received immediate irrigation at the time of injury (inlcuding 5 of the 6 cases occuring in the workplace), seven were irrigated by the primary care department. In one case the initial irrigation was delayed until review by an ophthalmologist, unfortunately one of the cases taking greater than 12 hrs to present. Ten eyes were re-irrigated by ophthalmology. Six underwent eyelid eversion with removal of debris as appropriate. Table 1 shows best corrected visual acuity (BCVA) in the affected eye at initial presentation. In a quarter this was worse than 6/60, although one third retained a BCVA of 6/12 or better.

Management by ophthalmology within the first 10 days

Table 2 summarises the non-surgical initial management of these cases. Follow up data from the 6 mth questionnaire was received in 10 patients. The BCVA at final follow up is shown in Table 1. Half of patients had a BCVA of 6/12 or better 6 mths post injury. In 20% BCVA was worse than 6/60. Figure 2 shows the recorded complications during the six months follow injury. Central corneal pannus or scar was the most frequent problem in 70%. In two cases 6 mth BCVA was 6/5. In the remainder the reason for the reduction in vision was reported as being secondary to the associated corneal pathology. Table 3 summarises the non-surgical and surgical management modalities used between 10 days and final follow up. AMG was used in 50% of eyes between 10 days and 6 months. Limbal stem cell graft was performed in 20%. In total three (30%) eyes had required two surgical procedures at final follow up, three had required one.

DISCUSSION

This study estimates the UK annual incidence rate of severe chemical corneal injury is 0.02 per 100 000. This incidence is low. A degree of underascertainment is a feature of studies of this nature, however, active surveillance as practiced by the BOSU has been shown to be more effective than other methods. [START_REF] Thacker | A controlled trial of disease surveillance strategies[END_REF][START_REF] Vogt | Comparison of an active and passive surveillance system of primary care providers for hepetitis, measles, rubella, and salmonellosis in Vermont[END_REF] Similar to previous surveillance studies the mean card return rate was high (78%) and questionnaire response rates were above 80%. Furthermore, the BOSU is generally well supported by reporting ophthalmologists, with previous estimated ascertainment rates of 75-95%. [START_REF] Foot | The British Ophthalmological Surveillance Unit: an evaluation of the first 3 years[END_REF] Based upon response rates it is safe to assume that ascertaiment in this study is likely to be similar to previous surveillance studies using the BOSU reporting system. The incidence rate reported is a minimum rate and it is possible that the true incidence may be up to 25% greater than this. Underreporting is usually attributed to random error (eg forgetting to report a case, misunderstanding the case definition), reluctance to participate, or management of cases by ophthalmologists who do not receive BOSU reporting cards [START_REF] Foot | The British Ophthalmological Surveillance Unit: an evaluation of the first 3 years[END_REF][START_REF] Imrie | Surveillance of intraocular foreign bodies in the UK[END_REF] rather than systematic error which would bias the representative nature of this population based co-hort. Even accounting for any potential under-ascertainment the reported incidence is lower than might be anticipated from the limited previous data [START_REF] Morgan | Chemical burns of the eye: causes and management[END_REF][START_REF] Davis | Topical steroid use in the treatment of ocular alkali burns[END_REF] and probably reflects a true reduction in the UK incidence of severe chemical corneal injury Due to the small number of reported cases in this study it is difficult to come to firm conclusions regarding the current presentation and management of severe chemical corneal injury in the UK. In accordance with epidemiological data from other studies, this survey confirmed that severe chemical corneal injury is seen more commonly in men (75% of cases) mainly of working age (66.7%), with the injury most often occurring at work (50%) or following assault (33.3%) and an alkaline substance most commonly implicated.

Previous studies have show severe chemical eye injuries are more common in males between 16 and 45 yrs, occurring accidentally at work or at home, or as the result of deliberate assault. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF][START_REF] Kuckelkorn | Emergency treatment of chemical and thermal eye burns[END_REF][START_REF] Morgan | Chemical burns of the eye: causes and management[END_REF][START_REF] Kuckelkorn | Chemical and thermal eye burns in the residential area of RWTH Aachen. Analysis of accidents in one year using a new automated documentation of findings[END_REF] A retrospective study of 221 chemical injuries by Morgan et al [START_REF] Morgan | Chemical burns of the eye: causes and management[END_REF] in the UK showed alkali injuries were twice as common as acid injuries and men were affected 75.6% of the time. In his study, 63% of injuries occurred in the workplace and 33% at home, 10.6%

were secondary to assault. None of their reported cases were classed as severe. Kucklehorn published a subsequent series of 236 eyes from Germany in which 70% of chemical injuries occurred in males between aged 16-45yrs. [START_REF] Kuckelkorn | Chemical and thermal eye burns in the residential area of RWTH Aachen. Analysis of accidents in one year using a new automated documentation of findings[END_REF] Industrial accidents accounted for 61% of injuries and household accidents 37%. A second series was limited to severe chemical injuries and showed these most often resulted from industrial accidents in males, aged 20-40 years. [START_REF] Kuckelkorn | Chemical and thermal eye burns in the residential area of RWTH Aachen. Analysis of accidents in one year using a new automated documentation of findings[END_REF] Only one patient was wearing any eye protection at the time of injury similar to previous reports of chemical eye injury which show the vast majority of patients are not wearing any protection at the time of injury. [START_REF] Blais | Treating chemical eye injuries[END_REF] Lack of eye protection is a major risk for the development of a severe chemical injury should exposure occur. Legislation in the UK enforces appropriate use of eye protection in the workplace, [START_REF] Imrie | Surveillance of intraocular foreign bodies in the UK[END_REF] Formal education, reinforcement, compulsory use and formal legislation have been shown to be effective in improving compliance. 19.20 In addition safer working practices, hazard warnings and safety advice on chemical product packaging can help. [START_REF] Lipscomb | Effectiveness of interventions to prevent work-related eye injuries[END_REF][START_REF] Stevens | Eye Injuries: Causes and Prevention[END_REF] Immediate irrigation following chemical eye injury is probably the single most important intervention influencing outcome more than any other therapeutic approach. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF][START_REF] Kuckelkorn | Emergency treatment of chemical and thermal eye burns[END_REF][START_REF] Blais | Treating chemical eye injuries[END_REF] Three-quarter of our patients received immediate irrigation at the time of injury, including all but one of those that occurred in the workplace.

It suggests occupational and public health measures in the UK highlighting the importance of this are partially effective.

Early management aims to reduce inflammatory cell infiltration and promote corneal re-epithelialisation, keratocyte proliferation and collagenase production. [START_REF] Wagoner | Chemical Injuries of the Eye: current concepts in pathophysiology and therapy[END_REF] Longer term management aims to restore the visual function by managing the effects of limbal stem cell deficiency, preserving tear production and addressing additional complicating factors. [START_REF] Azuara-Blanco | Amniotic membrane transplantation for ocular surface reconstruction[END_REF][START_REF] Chiou | Management of conjunctival cicatrizing diseases and severe ocular surface dysfunction[END_REF][START_REF] Cauchi | A systematic literature review of surgical interventions for limbal stem cell deficiency in humans[END_REF] Initial treatment involves a combination of preservative-free topical antibiotic, steroids, cycloplegics and pressure lowering treatment as appropriate. [START_REF] Kuckelkorn | Emergency treatment of chemical and thermal eye burns[END_REF] Topical ascorbate, citrate, systemic vitamin C and tetracycline derivatives may promote collagen remodeling, reduce the incidence of ulceration and prevent progression of established corneal ulceration. [START_REF] Ralph | Chemical injuries o f the eye[END_REF][START_REF] Pfister | The efficacy of ascorbate treatment after severe experimental alkali burns depends upon the route of administration[END_REF][START_REF] Pfister | Polymorphonuclear leucocyte inhibition by citrate, other heavy metal chelators, and trifluoperazine: evidence to support calcium binding protein involvement[END_REF] In this survey all patients received initial treatment with topical antibiotic and steroid, with preservative free varieties selected in half of cases. Topical citrate and systemic tetracycline derivatives were used in one quarter of the patients.

Surgical procedures reported in this survey included amniotic membrane graft (AMG), limbal stem cell graft, oral mucosa graft and fornix reconstruction.

AMG was the most commonly reported surgical procedure. AMG is recognised to promote epithelisation, prevent conjunctival adhesions and aid conjunctival surface reconstruction. [START_REF] Kuckelkorn | Chemical and thermal eye burns in the residential area of RWTH Aachen. Analysis of accidents in one year using a new automated documentation of findings[END_REF][START_REF] Azuara-Blanco | Amniotic membrane transplantation for ocular surface reconstruction[END_REF][START_REF] Chiou | Management of conjunctival cicatrizing diseases and severe ocular surface dysfunction[END_REF][START_REF] Cauchi | A systematic literature review of surgical interventions for limbal stem cell deficiency in humans[END_REF] Limbal stem cell graft was used in only two patients, but may have been required later as inflammation of the ocular surface induced by chemical burns has a negative impact in the survival of limbal stem cells. [START_REF] Cauchi | A systematic literature review of surgical interventions for limbal stem cell deficiency in humans[END_REF] Six months following injury BCVA was impaired to below 6/12 in half of patients, with two suffering very severe visual loss (worse than 6/60).

Reduced vision was attributed in all cases to the corneal pathology indicating substantial ocular morbidity and visual sequelae may be the consequence of severe chemical corneal injury.

Initial questionnaire data was received in thirty one patients in total. Of these nineteen were excluded from analysis for a variety reasons. Five of these were non-duplicates cases, which met the inclusion criteria, but occurred out with the study period. Summary of their clinical information, supplements the data from the included patients and shows they were broadly similar to those that occurred in the study period.

This study suggests that severe chemical injury is rare in the UK, occurring less often than previously. It seems that measures to enforce safe use of chemicals at work are generally enforced and effective, but when injury does occur it is evident that significant ocular morbidity and visual sequelae can result.

TITLES AND LEGENDS TO FIGURES

1 .

 1 Total loss of the corneal epithelium, and 2. Corneal haziness obscuring iris detail or worse, and 3. Over 120 o of limbal ischaemia This equated to Grade 3 or 4 on the Hughes-Roper-Hall classification scale.

Figure 1 .Figure 2 .

 12 Figure 1. The Clinical Features of Reported Patients with a Severe Chemical

  Figure 1

Table 1 .

 1 The Best Corrected Visual Acuity (BCVA) for Reported Patients with a Severe Chemical Corneal Injury at Presentation Compared to 6 months Details of the presenting clinical features in the 12 eyes is illustrated in Figure1. For inclusion corneal epithelial loss was total in all patients, 58.3% had 240-360 o of limbal ischaemia and two-thirds showed 50-100% of conjunctival epithelial loss. Four were referred from the presenting unit for a specialist corneal and external eye disease opinion.

	Following Injury
	Patient	BCVA at Presentation	BCVA 6 mths Following Injury
	1	6/9	6/12
	2	CF	Not available
	3	6/9	6/9
	4	HM	Not available
	5	6/18	6/18
	6	6/60	6/60
	7	6/18	6/5
	8	6/12	6/6
	9	6/9	6/36
	10	POL	CF
	11	6/18	6/12
	12	6/24	POL

Table 2 .

 2 The Initial Non-Surgical Management Reported in Patients with a All eyes received topical steroid and antibiotic either preserved or unpreserved. Topical ascorbate and/or systemic vitamin C was used in 83.3%, five received both. Five eyes received surgical treatment in the first 10 days. Two underwent division of symblepharon with a glass rod, two had an amniotic membrane graft (AMG). One eye was managed with debridement of the conjunctival tissue encroaching on the cornea.

	Severe Chemical Corneal Injury
		Non-Surgical Treatment	Number of patients
			(n=12)
	Topical	Steroid preserved	6
		Steroid unpreserved	6
		Antibiotic preserved	6
		Antibiotic unpreserved	6
		Citrate	3
		Ascorbate	6
		Anti-glaucoma	2
		Dilatation	8
	Systemic Vitamin C	9
		Tetracycline derivatives

Up and Management by ophthalmology 10 days-6mths.

Table 3 .

 3 The Non-Surgical and Surgical Management Reported from 10 days

	Following Injury to Final Follow-Up at 6 months in Patients with a Severe
	Chemical Corneal Injury.

Clinical Details of the Patients Excluded who Met the Inclusion Criteria but Occurred Outwith the Study Period.

	6/9 in all patients except for one with a BCVA of hand-movements. Corneal
	pathology was the reported cause of reduced vision.
	Five patients were excluded from analysis as the reported injury had occurred
	out with the study period. Their injury had occurred 1 mth-2yrs prior to the
	study period. All were males of working age, 4 injuries occurred during paid
	employment, 1 following assault. None were wearing eye protection at the
	time of injury, 4 received immediate irrigation. The BCVA at presentation
	ranged from 6/12 to 6/60, 1 had 240 o -360 o limbal ischaemia, 2 had 50-100%
	conjunctival loss. All received initial treatment with topical steroid or antibiotic,
	3 received topical ascorbate and/or systemic vitamin C. An AMG was used to
	treat 1 patient, 2 received a limbal stem cell graft. Six month BCVA was 6/6 or

Table 1 .

 1 The Best Corrected Visual Acuity (BCVA) for Reported Patients with a Severe Chemical Corneal Injury at Presentation Compared to 6 months

	Following Injury.

Table 2 .

 2 The Initial Non-Surgical Management Reported in Patients with a Severe Chemical Corneal Injury.

Table 3 .

 3 The Non-Surgical and Surgical Management Reported from 10 days Following Injury to Final Follow-Up at 6 months in Patients with a Severe Chemical Corneal Injury.

ACKNOWLEDGEMENTS

We are very grateful for the support of the British Ophthalmological Surveillance Unit. This work was supported by The Iris Fund for Prevention of Blindness and a grant from the Speed Pollock Memorial Trust, for which we are grateful. We thank the following ophthalmologists who reported cases in this study: Dr Adams, Mr Ahmed, Mr Allan, Mr Ayliffe, Mr Bates, Mr Azuara-Blanco, Mr Blythe, Mr Clowes, Miss Corbett, Mr Dart, Mr Davey, Mr Dinakaran, Mr Fallon, Mr Freeman, Dr George, Mr Greenwood, Miss Hollick, Mr Hunter, Mr Jabir, Mr. James, Mrs. Kayali, Mr. Larkin, Mr. Matthew, Mr Lee, Mr McGinnity, Mr McKibbin, Mr Mathew, Mr Quinlan, Dr Ramaesh, Mrs Reynolds, Mr Rostron, Mr. Stannard, Ms Weber.

DECLARATIONS

This work has been presented at the RCOphth Congress 2008

Competing Interests: None declared.

All authors declare that the answer to the questions on your competing interest form are all No and therefore have nothing to declare This research was run through The British Ophthalmological Surveillance Unit

The BOSU, run by the Royal College of Ophthalmologists, aims to provide a methodological framework for the systematic investigation of the incidence and clinical features of rare eye conditions with significant public health or scientific importance. Individual investigators submit proposals and the BOSU steering committee determines which conditions will be surveyed. The scheme involves all consultant or associate specialist ophthalmologists with clinical autonomy in the UK. Each month they receive a report card with case definitions of all conditions currently under surveillance. Respondents indicate how many cases of each disorder they have seen (including if they have not seen any). Individual investigators are notified of positive reports and contact the reporting ophthalmologist directly, using a questionnaire to collect information about the reported case. This establishes the patient's eligibility for inclusion and confirms the diagnosis. By collecting unique identifiers, duplicate reports of the same case can be excluded.

This work was supported by The Iris Fund for Prevention of Blindness and a grant from the Speed Pollock Memorial Trust, who provided funding only.

The researchers remained independent from the funders All authors, external and internal, had full access to all of the data in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis.

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 to permit this article (if accepted) to be published in BJO and any other BMJPGL products and sublicences such use and exploit all subsidiary rights, as set out in our licence


Pankaj Muhammad Amer Awan

Kumar Agarwal

G Watson

Charles N J Mcghee

Gordon N Dutton

P K Agarwal

D G Watson

Charles Nj Mcghee

Penetration of topical and sub-conjunctival corticosteroids into

Keywords: Corticosteroids, aqueous penetration, topical steroids, subconjunctival injection, hydrophilic compounds, hydrophobic compounds

come

Introduction:

Corticosteroids, used cautiously, are one of the most potent and effective modalities of treatment available for ocular inflammation. [START_REF] Mcghee | Locally administered ocular corticosteroids: benefits and risks[END_REF] Systemic corticosteroids were introduced into ophthalmic clinical practice in the 1950s as a major advance in the control of ocular inflammation. [START_REF] Raizman | Corticosteroid therapy of eye disease. Fifty years later[END_REF] However, within a few years, a number of ophthalmic adverse effects, such as cataract and elevated intraocular pressure (IOP), had been reported. [START_REF] Valerio | The hazards of prolonged local cortisone therapy[END_REF][START_REF] Black | Posterior subcapsular cataracts induced by corticosteroids in patients with rheumatoid arthritis[END_REF][START_REF] Covell | Glaucoma induced by systemic steroid therapy[END_REF][START_REF] Becker | Elevated intraocular pressure following corticosteroid eye drops[END_REF][START_REF] Urban Rc | Corticosteroid-induced cataracts[END_REF] In order to optimize ocular drug delivery, while minimizing systemic adverse events, a diverse range of topical drops, ointments, delayed-release topical vehicles, intraocular, periocular and oral corticosteroid preparations have been developed over the last 65 years. [START_REF] Mcghee | Pharmacokinetics of ophthalmic corticosteroids[END_REF] However, despite the continuing development of techniques and vehicles for local administration of corticosteroids, both systemic and ocular adverse events continue to be reported with dermatological, inhaled and ocular corticosteroid preparations. [START_REF] Hill | Adverse effects from topical steroids[END_REF][START_REF] Lipworth | Systemic adverse effects of inhaled corticosteroid therapy: a systematic review and meta-analysis[END_REF][START_REF] Garbe | Association of inhaled corticosteroid use with cataract extraction in elderly patients[END_REF][START_REF] Mitchell | Inhaled corticosteroids, family history, and risk of glaucoma[END_REF][START_REF] Salminen | Review: systemic absorption of topically applied ocular drugs in humans[END_REF][START_REF] Carnahan | Ocular complications of topical, peri-ocular, and systemic corticosteroids[END_REF] Although non-steroidal anti-inflammatory drugs have been shown to challenge the therapeutic efficacy of corticosteroids in a number of ophthalmic conditions without the associated risk of elevated IOP, decreased wound strength or predisposition to infection, [START_REF] Flach | The effect of ketorolac tromethamine in reducing postoperative inflammation: double-mask parallel comparison with dexamethasone[END_REF][START_REF] Othenin-Girard | Dexamethasone versus diclofenac sodium eye drops to treat inflammation after cataract surgery[END_REF][START_REF] Koay | The emerging roles of topical non-steroidal anti-inflammatory agents in ophthalmology[END_REF] topical corticosteroids remain a fundamental component of the ophthalmic therapeutic armamentarium.

Most topically applied corticosteroids penetrate the eye via the cornea. [START_REF] Rosenblum | Ocular absorption of dexamethasone phosphate disodium by the rabbit[END_REF] Corneal penetration studies conducted in un-anaesthetized albino rabbits have described transfer through the epithelium as the rate limiting step for drug absorption for hydrophilic compounds, whereas transfer through the stroma is rate limiting for hydrophobic compounds. However, very low molecular weight compounds demonstrate rapid uptake into the aqueous humour despite the lipid-like barrier imposed by the corneal epithelium. These results parallel the findings of similar in vivo studies and are consistent with a currently proposed 'pore' model for the penetration of drugs through the cornea which demonstrates both a partition coefficient and molecular weight dependency on the permeability of the cornea to transported compounds. [START_REF] Grass | Mechanisms of corneal drug penetration. I: In vivo and in vitro kinetics[END_REF] This view can be supported by in vitro observations of the penetration of hydrocortisone, conjugated to polyethylene glycols of increasing chain length, through bovine cornea. [START_REF] Foroutan | The in vitro evaluation of polyethylene glycol esters of hydrocortisone 21-succinate as ocular prodrugs[END_REF] In a rabbit model study corneal penetration of dexamethasone was increased after photorefractive surgery [START_REF] Maitchouk | Corneal pharmacodynamics after photorefractive keratectomy and laser in situ keratomileusis in rabbits[END_REF] whereas in another animal study there was no difference in penetration after photorefractive keratectomy. [START_REF] Mcdermott | The intraocular penetration of dexamethasone after photorefractive keratectomy[END_REF] The clinical benefits and adverse events associated with corticosteroid preparations have been well documented but their basic pharmacokinetics in the human eye have yet to be fully elucidated. An increasing amount of literature has addressed this issue, particularly over the last 20 years. [START_REF] Mcghee | Pharmacokinetics of ophthalmic corticosteroids[END_REF][START_REF] Watson | Penetration of topically applied dexamethasone alcohol into human aqueous humor[END_REF][START_REF] Kristinsson | Dexamethasone-cyclodextrin-polymer co-complexes in aqueous eye drops. Aqueous humor pharmacokinetics in humans[END_REF][START_REF] Weijtens | Intraocular penetration and systemic absorption after topical application of dexamethasone disodium phosphate[END_REF][START_REF] Mcghee | Penetration of synthetic corticosteroids into human aqueous humour[END_REF][START_REF] Leibowitz | Penetration of topically administered prednisolone acetate into the human aqueous humor[END_REF][START_REF] Mcghee | Penetration of topically applied prednisolone sodium phosphate into human aqueous humour[END_REF][START_REF] Watson | Penetration of topically applied betamethasone sodium phosphate into human aqueous humour[END_REF][START_REF] Jain | Ocular penetration of hydrocortisone and dexamethasone into the aqueous humour after subconjunctival injection[END_REF][START_REF] Debnath | Concentration of clobetasone butyrate in aqueous humour[END_REF] Much of the knowledge of these drugs has been gained by obtaining data from rabbit models, [START_REF] Leopold | Methyl and fluoro substituted prednisolones in the blood and aqueous humor of the rabbit[END_REF][START_REF] Wine | The ocular uptake of subconjunctivally injected C14 hydrocortisone. Part 1. Time and major route of penetration in a normal eye[END_REF][START_REF] Mccartney | An autioradiographic study of the penetration of subconjunctivally injected hydrocortisone into the normal and inflamed rabbit eye[END_REF][START_REF] Murdick | Ocular penetration studies. II. Topical administration of prednisolone[END_REF][START_REF] Short | Ocular penetration studies. I. Topical administration of dexamethasone[END_REF][START_REF] Mcdonald | Comparative toxicity of dexamethasone and its tertiary butyl acetate ester after topical ocular instillation in rabbits[END_REF][START_REF] Krupin | Ocular penetration in rabbits of topically applied dexamethasone[END_REF][START_REF] Kupferman | Topically applied steroids in corneal disease. 3. The role of drug derivative in stromal absorption of dexamethasone[END_REF][START_REF] Green | Prednisolone phosphate penetration into and through the cornea[END_REF][START_REF] Kupferman | Topically applied steroids in corneal disease. IV. The role of drug concentration in stromal absorption of prednisolone acetate[END_REF][START_REF] Kupferman | Topically applied steroids in corneal disease. V.Dexamethasone alcohol[END_REF][START_REF] Hull | Permeability of the isolated rabbit cornea to corticosteroids[END_REF][START_REF] Leibowitz | Anti-inflammatory effectiveness in the cornea of topically administered prednisolone[END_REF][START_REF] Sieg | Corneal absorption of fluorometholone in rabbits. A comparative evaluation of corneal drug transport characteristics in anesthetized and unanesthetized rabbits[END_REF][START_REF] Unlu | Scleral permeability to hydrocortisone and mannitol in the albino rabbit eye[END_REF][START_REF] Johansen | A bioavailability comparison in rabbits after a single topical ocular application of prednisolone acetate formulated as a high-viscosity gel and as an aqueous suspension[END_REF][START_REF] Druzgala | Ocular absorption and distribution of loteprednol etabonate, a soft steroid, in rabbit eyes[END_REF] but on account of differences in anatomy, and technical aspects of experimental studies, animal results can vary significantly from human studies. Such differences include the thinner rabbit cornea, lower rabbit blink rate, the effect of general anaesthetic, the effect of upright or recumbent position, the vascularity of the rabbit orbital plexus and the small rabbit body mass. [START_REF] Sieg | Corneal absorption of fluorometholone in rabbits. A comparative evaluation of corneal drug transport characteristics in anesthetized and unanesthetized rabbits[END_REF][START_REF] Smolin | High doses of subconjunctival corticosteroid and antibody-forming cells in the eye and draining lymph nodes[END_REF][START_REF] Sugar | Experimental corneal wound strength[END_REF][START_REF] Levine | Orbital infusion of steroids in the rabbit[END_REF] It has also been demonstrated that the rabbit cornea becomes significantly less permeable with age, particularly for large hydrophilic compounds, [START_REF] Ke | Age-related permeability changes in rabbit corneas[END_REF] suggesting that direct extrapolation from data on young laboratory animals to the elderly human cornea is of limited value. In general, measurements of corticosteroid concentration in rabbit eyes [START_REF] Leopold | Methyl and fluoro substituted prednisolones in the blood and aqueous humor of the rabbit[END_REF][START_REF] Short | Ocular penetration studies. I. Topical administration of dexamethasone[END_REF][START_REF] Green | Prednisolone phosphate penetration into and through the cornea[END_REF][START_REF] Leibowitz | Kinetics of topically administered prednisolone acetate. Optimal concentration for treatment of inflammatory keratitis[END_REF][START_REF] Kupferman | Biological equivalence of ophthalmic prednisolone acetate suspensions[END_REF][START_REF] Schoenwald | A bioavailability comparison in rabbits of two steroids formulated as high-viscosity gels and reference aqueous preparations[END_REF][START_REF] Schoenwald | Effect of particle size on ophthalmic bioavailability of dexamethasone suspensions in rabbits[END_REF] tend to be significantly higher than those recorded in humans. [START_REF] Watson | Penetration of topically applied dexamethasone alcohol into human aqueous humor[END_REF][START_REF] Kristinsson | Dexamethasone-cyclodextrin-polymer co-complexes in aqueous eye drops. Aqueous humor pharmacokinetics in humans[END_REF][START_REF] Weijtens | Intraocular penetration and systemic absorption after topical application of dexamethasone disodium phosphate[END_REF][START_REF] Mcghee | Penetration of synthetic corticosteroids into human aqueous humour[END_REF][START_REF] Leibowitz | Penetration of topically administered prednisolone acetate into the human aqueous humor[END_REF][START_REF] Mcghee | Penetration of topically applied prednisolone sodium phosphate into human aqueous humour[END_REF][START_REF] Watson | Penetration of topically applied betamethasone sodium phosphate into human aqueous humour[END_REF] In relation to systemic administration, the local administration of ocular corticosteroids theoretically enables the use of smaller doses for equivalent or greater local corticosteroid concentration, more target-specific drug application, and reduced risk of systemic adverse events. The minimal effective concentration of corticosteroid for treating different ocular inflammatory conditions has not been established for the commonly used corticosteroid formulations but the highest concentrations in human aqueous humour (1130 ng/ml maximal level) have been recorded following topical application of 1% prednisolone acetate. [START_REF] Leibowitz | Penetration of topically administered prednisolone acetate into the human aqueous humor[END_REF] This review article discusses the penetration of different ocular corticosteroids into human aqueous humour along with the therapeutic implications of these findings. A systematic review of literature indexed by Ovid MEDLINE & EMBASE was performed up to December 2008.

Penetration of topical ocular corticosteroids into human aqueous humour: (see table and figure)

Dexamethasone alcohol 0.1% Dexamethasone alcohol 0.1% [Maxidex, Alcon] is an effective topical corticosteroid and its penetration into the aqueous humour of human subjects has been evaluated by using gas chromatography combined with mass spectrometry (GCMS). Dexamethasone achieved its peak concentration in aqueous humour between 91 and 120 minutes following instillation (mean concentration, 31 ng/ml) and was still detectable in the aqueous 12 hours after instillation. [START_REF] Watson | Penetration of topically applied dexamethasone alcohol into human aqueous humor[END_REF] Dexamethasone-cyclodextrin-polymer co-complex 0.32%:

In another human study an aqueous drop containing dexamethasone-cyclodextrin-polymer cocomplexes 0.32% [Dexamethasone, Sigma Chemical; 2-hydroxypropyl-βcyclodextrin, Wacker-Chemie; hydroxypropyl methylcellulose, Mecobenzon] was used in the patients undergoing cataract surgery. By performing liquid chromatography, it was demonstrated that this formulation improved the aqueous humour penetration of dexamethasone (mean concentration of 140 ng/ml in 150 minutes) approximately 2.6 fold, when compared with dexamethasone alcohol 0.1% (Maxidex, Alcon), by enhancing both solubility in the formulation vehicle and permeability through the cornea. [START_REF] Kristinsson | Dexamethasone-cyclodextrin-polymer co-complexes in aqueous eye drops. Aqueous humor pharmacokinetics in humans[END_REF] Dexamethasone disodium phosphate 0.1%:

Weijtens et al measured dexamethasone disodium phosphate 0.1% [brand name not given]

concentration in aqueous humour, vitreous and serum by means of radioimmunoassay. The mean dexamethasone concentrations in the aqueous humor, vitreous, and serum were 30.5 ng/ml (range, 7.1-57.7 ng/ml), 1.1 ng/ml (range, 0.0-1.6 ng/ml), and 0.7 ng/ml (range, 0.0-1.2 ng/ml), respectively. [START_REF] Weijtens | Intraocular penetration and systemic absorption after topical application of dexamethasone disodium phosphate[END_REF] Interestingly in spite of being a hydrophilic preparation it performs as well as the preceding dexamethasone preparation which is lipophilic. These results indicated that the penetration of dexamethasone into vitreous humor after repeated drop application was small in comparison to sub-conjunctival administration, which was 72.5 ng/ml. [START_REF] Weijtens | High concentration of dexamethasone in aqueous and vitreous after subconjunctival injection[END_REF] Despite frequent instillation the dexamethasone concentration in the aqueous humor was far lower than after a subconjunctival injection with dexamethasone disodium phosphate. [START_REF] Weijtens | Intraocular penetration and systemic absorption after topical application of dexamethasone disodium phosphate[END_REF]

Prednisolone acetate 1%:

McGhee et al utilised GCMS to measure the intra-ocular penetration of prednisolone acetate 1%

[Predforte, Allergen] into the aqueous humour of human volunteers undergoing routine cataract extraction. [START_REF] Mcghee | Penetration of synthetic corticosteroids into human aqueous humour[END_REF] A mean peak concentration of 669.9 ng/ml was attained within two hours of application and levels of 28.6 ng/ml were still detected more than 24 hours after instillation of one drop. Acetate was largely converted to prednisolone alcohol during passage through the cornea. [START_REF] Mcghee | Penetration of synthetic corticosteroids into human aqueous humour[END_REF] In a separate study, a single standardized drop of 1.0% prednisolone acetate [Econopred plus, Alcon] labeled with tritiated thymidine was administered topically to one eye of 58 patients shortly before elective cataract extraction. By using scintillation spectrometer, peak drug concentration in aqueous humor was 1130 ng/ml, which occurred 30 to 45 minutes after instillation of the medication. [START_REF] Leibowitz | Penetration of topically administered prednisolone acetate into the human aqueous humor[END_REF] Prednisolone sodium phosphate 0.5%:

GCMS has also been utilised to determine the penetration of topically applied prednisolone sodium phosphate 0.5% [Predsol, Glaxo] into human aqueous humour. Detectable levels of prednisolone were measured in the aqueous humour within 15 minutes of administration. Peak aqueous concentrations of 25.6 ng/ml were much lower than those achieved by topical prednisolone acetate 1.0% and occurred between 90 and 240 minutes. The corticosteroid could not be detected in samples taken 10 hours or more after topical administration. [START_REF] Mcghee | Penetration of topically applied prednisolone sodium phosphate into human aqueous humour[END_REF] Betamethasone sodium phosphate 0.1%:

Watson et al also used GCMS to determine the absorption of topically applied betamethasone sodium phosphate 0.1% [Betnesol, Glaxo] into the aqueous humour of human subjects undergoing routine intraocular surgery. The betamethasone concentration was greatest in the interval 91-120 minutes following topical administration (mean peak concentration = 7.7 ng/ml). However, at 12 hours post instillation the mean concentration of betamethasone was 2.5 ng/ml and detectable levels were still measureable in the aqueous humour 24 hours after application (mean concentration 0.4 ng/ml). [START_REF] Watson | Penetration of topically applied betamethasone sodium phosphate into human aqueous humour[END_REF]

Fluorometholone alcohol 0.1%:

The penetration of fluorometholone alcohol 0.1% [FML, Allergan] into aqueous humour was determined using the GCMS. The peak aqueous humour level of fluorometholone was 5.1 ng/ml between 31 -60 minutes and significant concentrations of fluorometholone (mean level 4.3 ng/ml) were detected between 181 -240 minutes. [START_REF] Mcghee | Penetration of synthetic corticosteroids into human aqueous humour[END_REF] These levels are very low when compared with the levels resulting from application of the equivalent strength 0.1% dexamethasone drops.

There are no further studies to inform of its concentration after 10 hours.

Loteprednol etabonate 0.2% & 0.5%:

Loteprednol, is a so called 'soft' steroid, belongs to a unique class of corticosteroids with a metabolically labile 17β-chloromethyl ester, which is designed to be hydrolysed to a metabolically inactive carboxylic acid moiety. [START_REF] Druzgala | Ocular absorption and distribution of loteprednol etabonate, a soft steroid, in rabbit eyes[END_REF] In a rabbit eye study, concentrations of loteprednol etabonate and its metabolites were highest in the cornea, and so was the ratio of metabolites to unchanged drug, suggesting that the primary site of deactivation of the topically applied drug is the corneal tissue. A substantial amount of metabolites was also detected in the iris-ciliary body, although these were lower than in the cornea. The amount of drug and metabolites in the aqueous humour was low. [START_REF] Druzgala | Ocular absorption and distribution of loteprednol etabonate, a soft steroid, in rabbit eyes[END_REF] Unfortunately, to date no published human studies have determined its aqueous humour concentration following topical application.

Clobetasone butyrate 0.1% & betamethasone phosphate ointment 0.1%:

The concentrations of clobetasone butyrate 0.1% [Eumovate, Glaxo] and betamethasone phosphate 0.1% [Betnesol, Glaxo] have been measured by a radioimmunoassay technique in aqueous humour of patients undergoing cataract extraction 12.5 to 18.5 hours after application into the lower conjunctival sac of an ointment of the respective corticosteroid. Samples were assayed from 10 patients receiving clobetasone butyrate and 13 patients receiving betamethasone phosphate. There were measurable concentrations in only 2 aqueous samples in the former group, and both were 0.1 ng/ml. In the betamethasone group measurable aqueous concentrations were identified in 11 samples, the concentration ranged from 0.5 to 20.3 ng/ml and the highest concentration was found between 12.5 and 13.5 hours after application. [START_REF] Debnath | Concentration of clobetasone butyrate in aqueous humour[END_REF]

Hydrocortisone acetate 2.5% & dexamethasone sodium phosphate 0.4%:

The concentration of corticosteroids in aqueous humour was measured at various intervals after sub-conjunctival injection in a series of 130 patients undergoing cataract extraction by utilizing by spectro-colorimeter. Hydrocortisone acetate [Wycort, 0.5 ml of 2.5 per cent solution] and dexamethasone sodium phosphate [Dexona, 0.5 ml of 0.4 per cent solution] attained peak concentrations in the aqueous of 214.4 and 268.0 µg/ml respectively within 10 minutes.

Dexamethasone showed a uniformly higher penetration up to 24 hours (123 µg/ml) but the hydrocortisone effect lasted longer (20.5 µg/ml) for up to 7 days. 30

Therapeutic implications in the management of anterior segment diseases:

It is important, when comparing data concerning penetration of corticosteroids into aqueous humour to consider that systemic anti-inflammatory effect of both betamethasone and dexamethasone is five to seven times that of prednisolone. [START_REF] Pappa | Corticosteroid drugs[END_REF][START_REF] Haynes | Adrenocorticotrophic hormone: adrenocortical steroids and their synthetic analogs; inhibitors of the synthesis and actions of adrenocorticoid hormones[END_REF] The local anti-inflammatory potency of ocular corticosteroids has yet to be fully investigated, and while early work suggested that prednisolone acetate 1% had the greatest anti-inflammatory effect in experimental keratitis, [START_REF] Leibowitz | Anti-inflammatory effectiveness in the cornea of topically administered prednisolone[END_REF] subsequent studies demonstrated that fluorometholone acetate in a 1% formulation was equally efficacious in the same model. [START_REF] Kupferman | Fluorometholone acetate. Anew ophthalmic derivative of fluorometholone[END_REF] No data are yet available to determine the optimal corticosteroid concentrations required in various ocular inflammatory diseases. In the context of the paucity of well-constructed, prospective clinical trials comparing the efficacy of different corticosteroids, the above studies can be employed to provide guiding principles for the use of topical corticosteroids and for future trial design. To our knowledge there is no literature which compares relative efficacy of generic with branded topical steroids.

Ocular surface use:

Ocular surface diseases require corticosteroids to control inflammation and various types of topical corticosteroids are used. Fluorometholone alcohol 0.1% and loteprednol etabonate 0.5% are mild corticosteroids with low intraocular penetration. [START_REF] Mcghee | Penetration of synthetic corticosteroids into human aqueous humour[END_REF][START_REF] Druzgala | Ocular absorption and distribution of loteprednol etabonate, a soft steroid, in rabbit eyes[END_REF] It has been established that fluorometholone alcohol, which has a low likelihood of elevating IOP and penetrates into human aqueous humour to a lesser extent than prednisolone or dexamethasone, [START_REF] Mcghee | Pharmacokinetics of ophthalmic corticosteroids[END_REF] undergoes local ocular metabolism and consequent inactivation in the cornea. [START_REF] Iqbal | The metabolism of fluorometholone by bovine cornea[END_REF] According to corticosteroid penetration studies, fluorometholone alcohol 0.1%, loteprednol etabonate 0.5% , betamethasone phosphate 0.5% and prednisolone sodium phosphate 0.5% can be used for ocular surface diseases. In two different randomized controlled trial (RCT) loteprednol etabonate has shown excellent results in seasonal allergic and giant papillary conjunctivitis with minimal risk of transient intraocular pressure rise. [START_REF] Dell | A controlled evaluation of the efficacy and safety of loteprednol etabonate in the prophylactic treatment of seasonal allergic conjunctivitis. Loteprednol Allergic Conjunctivitis Study Group[END_REF][START_REF] Friedlaender | A double-masked, placebo-controlled evaluation of the efficacy and safety of loteprednol etabonate in the treatment of giant papillary conjunctivitis. The Loteprednol Etabonate Giant Papillary Conjunctivitis Study Group I[END_REF] Dexamethasone alcohol 0.1% and prednisolone sodium phosphate 0.5% are also used in allergic and atopic conjunctivitis depending on its severity but there are no trials so far to compare these preparations.

Eyelid margin disease with secondary conjunctival and corneal involvement is well characterised in adults and is termed blepharokeratoconjunctivitis. It has been treated with topical antibiotics along with flouromethalone alcohol 0.1%, or prednisolone sodium phosphate 0.5% but there is no clinical evidence to show comparative effectiveness. [START_REF] Viswalingam | Blepharokeratoconjunctivitis in children: diagnosis and treatment[END_REF] Episcleritis is idiopathic in the majority of cases, however very rarely there is an association with an underlying systemic disease like rheumatoid arthritis. Jab et al has described in a case series that fluorometholone 0.1% worked well in most of cases and if there was no response to treatment, then prednisolone acetate 1% was recommended. [START_REF] Jabs | Episcleritis and scleritis: clinical features and treatment results[END_REF] The role of topical corticosteroids in the management of ocular alkali burns remains controversial. Alkaline chemical burns vary in intensity and may be treated with preservative free prednisolone disodium phosphate 0.5% or dexamethasone sodium phosphate 0.1% along with other standardized treatment regimes during the first week following trauma. In an animal study Donshick et al found that topical corticosteroids if used from day 6 to day 21 following the injury were associated with an increase in number and severity of corneal ulceration. [START_REF] Donshik | Effect of topical steroids on ulceration in alkaliburned corneas[END_REF] Although in the case series by Davis et al have reported a study in which topical corticosteroids were used for longer duration with improved outcomes but oral vitamin C was used as an adjunct. [START_REF] Davis | Topical steroid use in the treatment of ocular alkali burns[END_REF] Dry eye is a multifactorial ocular surface disease with various manifestations and degrees of severity. Some individuals manifest mild or episodic symptoms that are easily controlled with an ocular lubricant. Others present with severe complications from keratoconjunctivitis sicca.

Although not without associated risks, Avunduk et al [START_REF] Avunduk | The comparison of efficacies of topical corticosteroids and nonsteroidal anti-inflammatory drops on dry eye patients: a clinical and immunocytochemical study[END_REF] have reported a randomised controlled trial that primarily surface active topical corticosteroids such as fluorometholone alcohol 0.1% have a clear beneficial effect both on the subjective and objective clinical parameters of moderate-to-severe dry eye patients. These effects were associated with the reduction of the inflammation markers of conjunctival epithelial cells. 69

Immune mediated corneal diseases and anterior uveitis:

According to the above drug penetration studies, prednisolone acetate 0.1% and dexamethasone alcohol 0.1% have good aqueous penetration and can be used in immune related corneal diseases and anterior uveitis.

The exact aetiology of disciform keratitis is controversial but it may be an infection of associated keratocytes and endothelium or an exaggerated hypersensitivity response to viral antigen (herpes simplex/ zoster). In double masked randomized trial Power et al have shown that the cumulative rate of healing was better and quicker in the steroid group (betamethasone 0.1%) when compared with the placebo group. [START_REF] Power | Acyclovir ointment plus topical betamethasone or placebo in first episode disciform keratitis[END_REF] However; it is not known how this affects the recurrence rate of active herpetic disease.

In anterior uveitis steroids are used to quell the inflammatory response. This is achieved by using a topical corticosteroid and a frequency depending on the severity of inflammation. Prednisolone acetate 1% or dexamethasone 0.1% is often the drug of first choice. Corticosteroid ointments such as betamethasone 0.1% or dexamethasone 0.1% are helpful at night. In very severe anterior uveitis, subconjunctival injection of dexamethasone sodium phosphate 0.4% is useful as it can attain and maintain high aqueous concentration for 24 hours. [START_REF] Jain | Ocular penetration of hydrocortisone and dexamethasone into the aqueous humour after subconjunctival injection[END_REF] The corticosteroids with poor aqueous penetration are not very effective for the control of intraocular inflammation.

Loteprednol etabonate 0.5% has been compared to prednisolone acetate 1% and was less effective than prednisolone acetate. However, the more favourable profile of loteprednol etabonate with respect to IOP increase may make it useful in many patients. [START_REF]Controlled evaluation of loteprednol etabonate and prednisolone acetate in the treatment of acute anterior uveitis. Loteprednol Etabonate US Uveitis Study Group[END_REF] Rimexolone 1% ophthalmic suspension was almost as effective as prednisolone acetate in the patients with anterior uveitis but prednisolone acetate was more likely to cause increase in IOP. 72

Postoperative use:

Prednisolone acetate 1% and dexamethasone alcohol 0.1% are the common topical corticosteroids which are used to control inflammation postoperatively. Prednisolone acetate 1%

achieves its highest aqueous level (669.9 ng/ml) within 120 minutes and maintains a significant level throughout 24 hours. Whereas dexamethasone alcohol 0.1% and dexamethasone phosphate 0.1% attain peak aqueous levels (30.5 -31 ng/ml; 20 times less than that of prednisolone acetate) within 55 to 120 minutes and detectable levels are seen at 12 hours.

Although dexamethasone is a more potent anti -inflammatory steroid than prednisolone with a greater binding affinity for glucocorticoid receptors, using non-invasive anterior chamber fluorophotometry in RCT, it was not possible to demonstrate any significant difference in its efficacy in protecting the blood-aqueous barrier after cataract extraction and posterior chamber lens implantation when compared to prednisolone acetate. [START_REF] Diestelhorst | Effect of dexamethasone 0.1% and prednisolone acetate 1.0% eye drops on the blood-aqueous barrier after cataract surgery: a controlled randomized fluorophotometric study[END_REF] Thus twice daily application of prednisolone acetate 1% may be suitable for uncomplicated postoperative cataract cases. In another randomized study 0.7% dexamethasone-cyclodextrin aqueous eye drops applied once daily was a more effective postoperative anti-inflammatory medication than 0.1% dexamethasone sodium phosphate applied three times a day. 74

Conclusion:

Ocular corticosteroids are widely used to control inflammation in different ocular conditions.

The corneal penetration and resultant aqueous humour concentrations are well known for the most of ocular corticosteroids in humans, and in the absence of clinical trials, this knowledge can be used to provide further guidance. However, we still do not know the degree of penetration of these steroids into the aqueous humour in the inflamed eye. Unfortunately corticosteroid induced glaucoma and cataract is a potential complication in susceptible individuals, and injudicious use of topical corticosteroids in ocular infection carries significant morbidity. The risk of glaucoma is relatively reduced with the new class of topical corticosteroids like loteprednol etabonate and rimexolone but their absorption and anti inflammatory effects are also decreased. Topical, subconjunctival, and sub-tenon application of corticosteroids are preferable to systemic administration in anterior segment diseases depending on the severity and level of inflammation.

The aqueous penetration of topical corticosteroids, their expected molar potencies and possible side effects can provide advice in their judicious use.

Table : Comparison of human aqueous humour concentration of corticosteroids following topical and subconjunctival application:

 :

	Drug	Route	Dose	No. Of	Mean Peak	Time	At 12	At 24	Reference
			(No. of	subjects	Aqueous	to	hours	hours
			drops)		Concentration	Peak
					(ng/ml)	(min)	(ng/ml)	(ng/ml)
	Dexamethasone	Drops	0.1% (1) 64	31	90 to	3.1	N/A †
	Alcohol					120
	Dexamethasone-	Drops	0.32%	47	140	150	N/A †	N/A †
	cyclodextrin-polymer co-		(1)
	complex
	Dexamethasone	Drops	0.1%(10) 10	30.5	55	N/A †	N/A †
	disodium
	phosphate
	Prednisolone	Drops	1% (1)	66	669.9	120	99.5	28.4
	Acetate
	Prednisolone	Drops	1% (1)	58	1130	30-45 N/A †	N/A †
	Acetate
	Prednisolone	Drops	0.5% (1) 93	25.6	90-	0	N/A †
	Sodium					240
	Phosphate
	Betamethasone	Drops	0.5% (1) 66	7.7	90-	2.5	0.4
	Phosphate					120
	Fluorometholone	Drops	0.1% (1) 22	5.1	31-60 N/A †	N/A †
	Alcohol
	Clobetasone	Ointment	0.1% (1) 10	0.1	810	0.1	N/A †
	Butyrate
	Betamethasone	Ointment	0.1% (1) 13	20.3	810	20.3	N/A †
	Phosphate
	Hydrocortisone	Subconjunctival 0.5ml (1) 130	214× 10 3	10	N/A †	103×
	Acetate 2.5%							10 3
	Dexamethasone	Subconjunctival 0.5ml (1) 130	268× 10 3	10	N/A †	123×
	Sodium							10 3
	Phosphate 0.4%
	†N/A: not available

Legends: