S. Ve Ramesh

Ocular biometry in occludable angles and angle closure glaucoma: a population based survey

Aim: To compare ocular biometric values in a population based sample of eyes with occludable angles, angle closure glaucoma, and normal subjects. Method: 2850 subjects from a population based glaucoma prevalence study underwent complete ocular examination including indentation gonioscopy. Ocular biometry was performed in all subjects classified to have occludable angles (n = 143); angle closure glaucoma (n = 22), and a random subgroup of 419 normal subjects. Ocular biometry readings between the groups were compared and statistically analysed using “t,” “z,” and Mann-Whitney U tests. Results: The mean age among subjects with occludable angles (54.43 (SD 9.53) years) and angle closure glaucoma (57.45 (8.5) years) was significantly higher (p<0.001) than normal subjects (49.95 (9.95) years). Axial length was shorter (p<0.001) in the occludable angle group (22.07 (0.69) mm) compared to the normal group (22.76 (0.78) mm). Anterior chamber depth (ACD) was shallower (p<0.001) among subjects with occludable angles (2.53 (0.26) mm) than normal subjects (3.00 (0.30) mm). Lens thickness (LT) was greater (p<0.001) in people with occludable angles (4.40 (0.53) mm) compared to normal subjects (4.31 (0.31) mm). No significant difference was noted in axial length, ACD (p = 0.451), and LT (p = 0.302) between angle closure glaucoma and occludable eyes. Conclusion: South Indian eyes with angle closure glaucoma and occludable angles seem to have significantly shorter axial lengths, shallower anterior chambers and greater lens thickness compared to the normal group.

Pseudoexfoliation in south India

Aim: To study the profile of pseudoexfoliation in a population based study. Method: 2850 consecutive subjects aged 40 years or older from a population based survey in a rural area of southern India underwent complete ophthalmic evaluation including history, visual acuity testing, refraction, slit lamp examination, applanation tonometry, gonioscopy, and dilated examination of the lens (including LOCS II grading of cataract), fundus, and optic disc. Patients with pseudoexfoliation syndrome were identified and their data were analysed with respect to age, sex, intraocular pressure, gonioscopic grading, cataract, and optic neuropathy. Results: 108 subjects had pseudoexfoliation syndrome (3.8 %). There was a significant increase in prevalence with age but no sex predilection. The condition was unilateral in 53 cases (49.1%) and bilateral in 55 cases (50.9%). 18 cases with pseudoexfoliation (16.7%) had high intraocular pressure (>21 mm Hg), 16 cases (14.8%) had occludable angles, and 14 cases (13%) had pseudoexfoliation glaucoma. There was a significantly higher prevalence of cataract among people with pseudoexfoliation compared to those without pseudoexfoliation (p = 0.014). Conclusion: The prevalence of pseudoexfoliation syndrome in the rural population of south India was 3.8%. Raised intraocular pressure was seen in 16.7% of people with pseudoexfoliation and glaucoma was present in 13%.

Methods and design of the Chennai Glaucoma Study.

PURPOSE To describe the methodology of a population-based study to estimate the prevalence of glaucoma in a rural and urban South Indian population and to study the genetics of glaucoma in this population. METHODS A sample size of 4758 each for rural and urban populations in the Indian state of Tamil Nadu was calculated. Eligible subjects aged 40 years and above from the rural study area covering 32 contiguous villages and the urban area comprising five random clusters in Chennai city are enumerated. Demographic data are collected in the field. A detailed clinical examination, including glaucoma diagnostic procedures, is conducted at the examination centre. Pedigree ascertainment and genetic studies are performed for subjects with occludable angles or glaucoma. Data are recorded in a computerised database. CONCLUSIONS This study is expected to result in an estimation of the prevalence and a better understanding of the genetics of glaucoma in this region.

Influence of tobacco use on cataract development

Aim: To study the influence of tobacco use on cataract formation in a rural South Indian population. Methods: 3924 subjects from the Chennai Glaucoma Study conducted in rural south India underwent a comprehensive eye examination, including Lens Opacities Classification System II grading. Information on tobacco use, type of tobacco (smoking and smokeless), duration and quantity of use was collected. Results: 1705 (male:female (M:F) 1106:599) people used tobacco and were significantly older (mean (standard deviation (SD)) age 55.80 (10.64) years) than non-users (52.23 (10.51); p<0.001). 731 (M:F 730:1) people smoked, 900 (M:F 302:598) used smokeless tobacco, and 74 (M:F, 74:0) used tobacco in both forms. The unadjusted and adjusted (age and sex) odds ratio (OR) for a positive history of tobacco use and cataract was 1.72 (95% confidence interval (CI) 1.51 to 1.96) and 1.39 (95% CI 1.15 to 1.68), respectively. The unadjusted OR for smokers and smokeless tobacco users was 1.04 (95% CI 0.88 to 1.23) and 2.74 (95% CI 2.31 to 3.26), respectively. The adjusted OR was 1.19 (95% CI 0.89 to 1.59) and 1.54 (95% CI 1.22 to 1.95), respectively. No significant association was noted between smoking and any particular type of cataract. Smokeless tobacco use was found to be significantly associated with nuclear cataract even after adjusting for age and sex (OR 1.67, p = 0.067, 95% CI 1.16 to 2.39). Conclusion: Tobacco use was significantly associated with cataract. Smoking was not found to be significantly associated with cataract formation; however, smokeless tobacco use was more strongly associated with cataract.

Prevalence of Retinitis Pigmentosa in South Indian Population Aged Above 40 Years

Purpose: The study was undertaken to evaluate the prevalence of retinitis pigmentosa (RP) in rural and urban South India. Methods: Seven thousand seven hundred and seventy four subjects aged 40 years or more from rural and urban Tamil Nadu, underwent comprehensive ophthalmic examination out of 9576 enumerated (81.17%). After a thorough ophthalmic examination, fundus photographs were taken for documentation. Statistical analysis was done using SPSS for Windows (ver 14). Results: 7461 (95.9%) subjects had fundus details seen in both eyes. Thirteen subjects (0.17%; 4 males, 9 females) were diagnosed as retinitis pigmentosa. Retinitis pigmentosa in the urban population was seen in approximately 1 in 930 persons, while 1 in 372 of rural subjects had the disorder. This figure is greater than other reports from the western populations and that of the conservative estimate of 1 in 4000. The age and gender adjusted prevalence rate of retinitis pigmentosa to national census 2001 was 0.155%. Eight subjects (61.53%) had visual acuity less than 3/60. Conclusion: Prevalence of RP in South India appears to be alarmingly higher in comparison to those seen in other parts of the world.

A Comparison of Participants and Non-Participants in the Chennai Glaucoma Study—Rural Population

Purpose: To study whether the difference in the demographic characteristics of participants and non-participants could result in biased prevalence estimates and associations. Aim: To compare the non-participant & participant characteristics, and to ascertain if non-response bias is present in the rural population of the Chennai Glaucoma Study (CGS). Methods: Rural participants and non-participants were compared with regard to socio-demographic variables (age, gender, religion, mother tongue, literacy and employment). Results: 4800 subjects aged 40 years or over were enumerated, 82% (3934: 45% male and 55% female) responded. Gender did not influence participation (adjusted OR–1.11, CI: .91–1.36). Subjects in the 70–79 year age group were more likely to respond (OR–1.76; CI–1.31–2.38). Hindus had a higher participation rate than Christians or Muslims (adjusted OR–2.63, CI: 1.80–3.84). The other predictors of participation were illiteracy (adjusted OR–1.44, CI: 1.22–1.70), unemployment (OR–1.28, CI: 1.04–1.58), place of residence (main villages) (OR–1.89, 95% CI: 1.59–2.25) and cottage industry-based villages (OR–6.66, 95% CI: 4.6–9.64). Conclusion: Based on our study findings, it does not seem likely that participation bias will affect the study results.

Effect of Cataract Surgery with Intraocular Lens Implant on Frequency Doubling Perimetry

Purpose: To study the effect of cataract surgery with intraocular lens (IOL) on frequency doubling perimetry (FDP). Methods: Patients aged 40 years or above seen at our outpatient clinic with no ocular pathology except for visually significant cataract and visual acuity 6/24 or better were eligible. They underwent FDP before and 4 to 6 weeks after cataract surgery with IOL. Results: Screening test: Mean scores by three different scoring methods were 1.82 (3.21), 2.80 (5.54), 4.18 (9.18) before and 0.22 (0.51), 0.26 (0.63), 0.26 (0.69) after surgery (p = 0.002 0.001, < 0.0001). Threshold test: Mean deviation (MD) and pattern standard deviation (PSD) were −5.23 (3.08) and 5.15 (2.78) before and 2.94 (2.49) (p < 0.0001) and 5.21 (1.780) (p = 0.63) after surgery. Conclusions: The screening test should be interpreted cautiously in the presence of cataract. On threshold testing, cataract surgery causes significant decrease in MD but no change in PSD.

Efficacy of a remote based computerised visual acuity measurement

Aim To determine the efficacy of a remotely operated computer-based logarithmic (logMAR) visual acuity chart. Methods Visual acuity was tested using a laptop or computer-based logMAR chart (COMPlog) for all subjects by two different methods. The methods differed by the physical presence and absence (remote) of an optometrist and in the mode of instructions provided. Remote access was obtained through the internet, using Teamviewer software to control the system linked to COMPlog and instructions were provided by telephone. The order of measurements and the eye to be tested was randomised. logMAR visual acuity and time taken were recorded. A questionnaire was used to assess the participants feedback. Results Intraclass correlation for visual acuity between the two methods (α=0.964, 95% CI 0.937 to 0.979). There was no statistically significant difference (p=0.648) in the median visual acuity measurement between the two methods (median difference 0.00, IQR 0.20 logMAR). The time taken between the two methods was not statistically significant (p=0.457). There was no significant difference in the responses to the questionnaire between the study methods (p=0.119). Conclusions Tele (remotely controlled) visual acuity measurement is as reliable as that measured with the physical presence of an optometrist.

Perimetric severity in hospital‐based and population‐based glaucoma patients

Background:  The aim was to compare the severity of glaucoma among newly diagnosed patients presenting to a hospital‐based glaucoma care centre (HBGS: Sankara Nethralaya, Medical Research Foundation) with that of age matched subjects from the population‐based Chennai Glaucoma Follow‐up Study (CGFS).

Frosted cylindrical lens induced artefact on Humphrey automated perimetry

Background: The aim of this study was to assess the effect of a cylindrical corrective lens with frosted sides on Humphrey automated perimetry performed with a translucent spectacle occluder in the contralateral eye.