Determinants of glaucoma awareness and knowledge in urban Chennai.

AIM: To assess the awareness and knowledge levels about glaucoma and its determinants in an urban population of Chennai in south India. MATERIALS AND METHODS: Chennai glaucoma study (CGS) was a population based prevalence study to estimate the prevalence of glaucoma in a rural and urban south Indian population. A total of 3850 subjects aged 40 years or above participated in the urban arm of CGS. A systematic random sample of 1926 (50.0%) subjects completed a questionnaire that assesses their awareness and knowledge level of glaucoma. Respondents "having heard of glaucoma" even before they were contacted/recruited for the study were defined as "aware" and respondents having some understanding of the eye disease were defined as "knowledgeable". RESULTS: Overall 13.5% were aware of glaucoma, the age-gender adjusted rate for awareness was 13.3% (95% CI: 11.57 to 15.03). Two clinicians graded knowledge on glaucoma, based on the subject's knowledge of risk factors, definitions and treatment aspects of glaucoma. Overall 8.7% had some knowledge about glaucoma. Among those who had knowledge 0.5% had good knowledge about glaucoma, 4% had fair knowledge and 4.2% had poor knowledge. We observed a very good agreement between the clinicians in grading knowledge (k =0.92). Determinants of glaucoma awareness and knowledge were higher levels of education, females, age, religion and family history of glaucoma. CONCLUSION: Awareness and knowledge about glaucoma was very low among the urban population of Chennai. We have found that younger subjects and men were less aware of glaucoma. Subjects with lower levels of education were less aware and knew less about glaucoma than their counterparts. The study findings stress the need for health education for effective prevention of blindness due to glaucoma.

Which is the optimal risk stratification system for surgically treated localized primary GIST? Comparison of three contemporary prognostic criteria in 171 tumors and a proposal for a modified Armed Forces Institute of Pathology risk criteria.

BACKGROUND: This study aims to validate and compare the performance of the National Institute of Health (NIH) criteria, Huang modified NIH criteria, and Armed Forces Institute of Pathology (AFIP) risk criteria for gastrointestinal stromal tumors (GISTs) in a large series of localized primary GISTs surgically treated at a single institution to determine the ideal risk stratification system for GIST. METHODS: The clinicopathological features of 171 consecutive patients who underwent surgical resection for GISTs were retrospectively reviewed. Statistical analyses were performed to compare the prognostic value of the three risk criteria by analyzing the discriminatory ability linear trend, homogeneity, monotonicity of gradients, and Akaike information criteria. RESULTS: The median actuarial recurrence-free survival (RFS) for all 171 patients was 70%. On multivariate analyses, size >10 cm, mitotic count >5/50 high-power field, tumor necrosis, and serosal involvement were independent prognostic factors of RFS. All three risk criteria demonstrated a statistically significant difference in the recurrence rate, median actuarial RFS, actuarial 5-year RFS, and tumor-specific death across the different stages. Comparison of the various risk-stratification systems demonstrated that our proposed modified AFIP criteria had the best independent predictive value of RFS when compared with the other systems. CONCLUSION: The NIH, modified NIH, and AFIP criteria are useful in the prognostication of GIST, and the AFIP risk criteria provided the best prognostication among the three systems for primary localized GIST. However, remarkable prognostic heterogeneity exists in the AFIP high-risk category, and with our proposed modification, this system provides the most accurate prognostic information.

Association of VEGF gene polymorphisms with diabetic retinopathy in a south Indian cohort.

BACKGROUND: Polymorphisms in vascular endothelial growth factor (VEGF) gene have been associated with diabetic retinopathy (DR) in various populations. A promoter polymorphism and a 3'UTR variation are studied for association with DR. MATERIALS AND METHODS: Type 2 diabetic patients with and without retinopathy were recruited. The -634C/G and 936C/T polymorphisms were genotyped by direct sequencing and their frequencies were analyzed using relevant statistical tests. RESULTS: No significant association was observed between genotypes, alleles and haplotypes of -634C/G and 936C/T polymorphisms and DR or its severity. However, C(-634)G genotype was found to increase the risk for DR in patients with microalbuminuria (OR: 8.9, 95% CI: 1.4, 58.3). CONCLUSION: Our study broadly suggests lack of association of VEGF gene polymorphisms with DR.

Diabetic retinopathy and IGF-1 gene polymorphic cytosine-adenine repeats in a Southern Indian cohort.

BACKGROUND/AIMS: Growth factors have been implicated in the pathogenesis of diabetic retinopathy (DR). IGF-1 is known to trigger a critical cascade of molecular events that initiate retinal angiogenesis. Increased vitreous IGF-1 levels have been correlated with the severity of ischemia-associated diabetic retinal neovascularization. In the present study, a cytosine-adenine (CA)(n) repeat in the promoter of the IGF-1 gene is studied for association with DR. METHODS: A total of 127 patients with retinopathy (cases: DR+) and 81 patients without retinopathy (controls: DR-) who had type 2 diabetes were recruited for the study. Patients underwent detailed clinical examination and DR was graded based on stereoscopic digital fundus photographs. Frequencies of alleles and genotypes between the two groups were analyzed for significance using relevant statistical tests. (CA)(17) and (CA)(18) repeats were the more frequent alleles. RESULTS: The frequency of the 18-repeat genotype was significantly higher in DR+ patients when compared to DR- patients and found to confer a 2.4 times (95% CI: 1.2-5.0) and 2.8 times (95% CI: 1.1-7.5) higher risk for developing DR and proliferative DR, respectively, when compared to <18-repeat genotypes. CONCLUSIONS: Our study suggests that the 18-repeat genotype is a susceptibility genotype for DR and its clinical severity in a Southern Indian cohort.

Intron 4 VNTR of endothelial nitric oxide synthase (eNOS) gene and diabetic retinopathy in type 2 patients in southern India.

A 27-bp variable number tandem repeat (VNTR) in intron 4 of endothelial nitric oxide synthase (eNOS) gene has been associated with the risk for developing diabetic retinopathy (DR) in various ethnic populations. Hundred and eighty seven patients with retinopathy (cases; DR+) and 188 patients without retinopathy (controls: DR-) from southern India who had type 2 diabetes mellitus (T2DM) for more than 10 years, were included in the study. We could neither find significant allelic association with clinical severity of DR nor with macular edema. Our results suggest lack of association of intron 4 VNTR of eNOS gene with DR in southern India.

Population norms for frequency doubling perimetry with uncorrected refractive error.

PURPOSE: To compare the effect of uncorrected refractive error on threshold estimation using frequency doubling perimetry (FDP) full-threshold N-30 with emmetropia among normal subjects. METHODS: One thousand two hundred ninety-nine subjects were enrolled from the Chennai Glaucoma Study, a population-based glaucoma prevalence study. Subjects underwent a comprehensive eye examination including the FDP full-threshold N-30 test. Normal subjects (with spherical equivalent refractive errors within +/-7 D) with no other ocular pathology were stratified into six groups based on the degree of myopia and hyperopia and compared with age-matched emmetropic controls. A subset of 22 subjects with higher refractive errors was assessed for within-subject effect on FDP parameters. The following FDP parameters were compared: mean deviation, pattern standard deviation, central threshold (CT), mean sensitivity (MS), paracentral points (PA), and peripheral threshold. RESULTS: The one-way analysis of variance between all refractive error groups and emmetropes showed no statistically significant difference for the mean deviation (p = 0.1002) and pattern standard deviation (p = 0.4789). FDP parameters did not show a statistically significant difference for between and within-group comparisons. The variability of FDP sensitivity (derived from the 95% confidence interval range) as a proportion of the threshold range of the instrument was 31, 41, 46, and 41% for CT, MS, PA, and peripheral sensitivity, respectively, without spectacle correction and 29, 34, 36, and 35% for CT, MS, PA, and peripheral sensitivity, respectively, with correction. The mean CT, PA, and peripheral sensitivity show a decreasing trend from central to periphery in all the refractive error groups and a similar trend was noted in the emmetropic controls. CONCLUSION: Between-subject (uncorrected ammetropes and age-matched emmetropes) and within-subject comparisons showed no statistically significant differences in any of the FDP parameters or in the contrast sensitivity estimates between the central and peripheral test locations. This finding is likely due to the high within-subject variability of FDP.

Patient satisfaction levels during teleophthalmology consultation in rural South India.

The application of new technologies for analysis of retinal images, neural networks for automated retinopathy grading, and teleophthalmology have been shown to have great value in ophthalmology. India has only one ophthalmic surgeon for every 107,000 population. Given this situation, teleophthalmology can play a vital role in addressing to the eye care needs of the country. The objective of this study was to assess patient satisfaction levels and factors influencing it during teleophthalmology consultation in India. A patient satisfaction questionnaire was prepared to assess the prominent aspects of patient satisfaction, including teleophthalmology screening, confidence in the technology used to transfer the fundus images, comprehensiveness of information available to the doctor in the central hub, and graded the opinion regarding the teleophthalmology. A cross-sectional survey among patients who attended a teleophthalmology screening conducted across eight villages in rural Tamilnadu. Responses were then subjected to qualitative analysis and conclusions made. The number of respondents was 348. Of this, 56.4% were males. The mean age of was 50 +/- 17 years. Age ranged from 2 years to 83 years. 44.4% of the respondents were satisfied with teleophthalmology screening. (95% confidence interval [CI]: 38.58%-49.42%) No association was found between age, gender, education, and occupation, respectively, with satisfaction levels. We found that patients who asked questions during the screening were 2.18 times more likely to be satisfied with teleophthalmology than those who did not (odds ratio [OR] = 2.19, 95% CI 1.37-3.5). This study highlights sentiments of the rural subjects when they underwent teleophthalmology consultations. This study provides valuable insights about patient's preferences and satisfaction levels with this newer technology.

Diabetic retinopathy in type II diabetics detected by targeted screening versus newly diagnosed in general practice.

INTRODUCTION: The aim of this study was to compare the occurrence of diabetic retinopathy in targeted screening diabetic patients (Group I) with newly diagnosed diabetic patients in general practice (Group II). MATERIALS AND METHODS: This was an observational cross-sectional study. Data were obtained from 25,313 subjects who participated in the diabetic screening camps, and 128 newly diagnosed diabetes who presented to the diabetic retinopathy screening camps in general practice in rural and urban south India. The study variables were collected from all patients who underwent eye examination from the target screening detected diabetics [(n = 173) Group I] and those newly diagnosed in general practice [(n = 128) Group II]. The variations in prevalence of diabetic retinopathy and sight-threatening diabetic retinopathy in Group I and Group II and the factors affecting it were identified. RESULTS: The occurrence of diabetic retinopathy was 6.35% (95% CI, 2.5-9.5) in Group I and 11.71% (95% CI, 5.6-16.4) in Group II. No significant difference was observed on occurrence of diabetic retinopathy, including sightthreatening retinopathy, in rural versus urban population and in Group I versus Group II. Patients diagnosed in general practice (Group II) with systolic blood pressure (BP) >140 were more likely to have retinopathy (P = 0.02). CONCLUSIONS: Diabetic retinopathy including sightthreatening complications was found at the time of diagnosis of diabetes in the targeted screening group as well as in newly diagnosed diabetics in the general practice group.

Prevalence of angle-closure disease in a rural southern Indian population.

OBJECTIVE: To estimate the prevalence of primary angle-closure glaucoma, primary angle closure (PAC), and primary angle-closure suspect (PACS) and its associated risk factors in a rural population in southern India. METHODS: Three thousand and nine hundred thirty-four (81.95%) of 4800 enumerated subjects aged 40 years or older underwent a complete ophthalmic examination, including compression gonioscopy. Glaucoma was diagnosed using International Society of Geographical and Epidemiological Ophthalmology classification. RESULTS: Data were analyzed for 3924 subjects (81.75%). Primary angle-closure glaucoma was diagnosed in 34 subjects (0.87%; 95% confidence interval [CI], 0.58 to 1.16) (27 women, 7 men). The mean intraocular pressure was 20.71 +/- 9.24 mm Hg. One subject (2.94%) was blind. Twenty-eight subjects (0.71%; 95% CI, 0.45 to 0.98) were diagnosed to have PAC (21 women, 7 men). Eleven subjects (39.3%) had an intraocular pressure greater than 21 mm Hg, 13 subjects (46.43%) had peripheral anterior synechiae, and 4 subjects (14.29%) had both. Two hundred forty-six subjects (6.27%; 95% CI, 5.51 to 7.03) had PACS (168 women, 78 men). Primary angle closure and primary angle-closure glaucoma were more common in women (age-adjusted odds ratio, 3.02; 95% CI, 1.66 to 5.51) with an increasing prevalence with age. Increasing intraocular pressure was associated with the disease (odds ratio, 1.14; 95% CI, 1.09 to 1.19). There was no association with hypertension and hyperopia. Axial length and anterior chamber depth were longer in the normal group than in the 3 groups with angle closure (P<.05). Women had shorter axial lengths than men (P<.001) in the angle closure groups. CONCLUSIONS: The overall prevalence of primary angle closures (PAC and primary angle-closure glaucoma) in a rural population of southern India was 1.58%. There was a female preponderance, and the disease tends to be asymptomatic.

Genotype-phenotype correlation analysis in retinoblastoma patients from India.

BACKGROUND: Genetic analysis has a beneficial impact on retinoblastoma management enabling definite risk assessment. However, information regarding genotype-phenotype correlation in retinoblastoma is limited. AIM: To analyze the retinoblastoma susceptibility gene for mutations in retinoblastoma patients and correlate the genotypes the phenotypes. METHODOLOGY: Eleven retinoblastoma patients, who underwent molecular genetic studies were classified into high, moderate or low disease severity groups based on phenotype. RESULTS: Seven patients had high disease severity and four moderate disease severity. Eleven truncating mutations were detected; six were in the N-terminus region of the retinoblastoma protein and two in the A/B pocket (p=0.03). CONCLUSIONS: No significant association between mutation type and disease severity could be established in the present study. However a positive correlation between location of the mutations in certain domains of the retinoblastoma protein and disease severity was observed. To the best of our knowledge this is the first genotype-phenotype correlation study in retinoblastoma patients from India.

How high is the non-response rate of patients referred for eye examination from diabetic screening camps?

AIM: To elucidate the rate of non-response among diabetics (recently diagnosed in rural diabetic screening camps) who were referred for eye examination to detect diabetic retinopathy. METHODS: At diabetic retinopathy screening camps, all patients underwent dilated fundus examination using binocular indirect ophthalmoscopy. RESULTS: Of the 4,111 known diabetics, only 2231(55%) patients attended the diabetic retinopathy screening camps. Likewise, of the 1076 newly detected diabetics, only 125 (11.6%) attended the diabetic retinopathy screening camps. CONCLUSIONS: Non-response of such a magnitude calls for creating greater awareness among masses on diabetes and its microvascular complications. Second, conducting simultaneous diabetes screening and diabetic retinopathy screening camps could minimize the dropout rate.

Prevalence of open-angle glaucoma in a rural south Indian population.

PURPOSE: To determine the prevalence of primary open-angle glaucoma (POAG) and the associated risk factors in a rural population in southern India. METHODS: Subjects aged 40 years or more (n = 3934) underwent a complete ophthalmic examination. Glaucoma was diagnosed according to the International Society of Geographical and Epidemiologic Ophthalmology classification. RESULTS: Complete data were available for 3924 subjects (response rate, 81.75%). In eyes with normal suprathreshold visual fields, the mean intraocular pressure was 14.29 +/- 3.32 mm Hg (97.5th and 99.5th percentiles, 21 and 25 mm Hg, respectively). The mean vertical cup-to-disc ratio was 0.39 +/- 0.17 (97.5th and 99.5th percentiles, 0.7 and 0.8, respectively). Sixty-four subjects had definite POAG (1.62%, 9.5% CI 1.42-1.82); 30 were men and 34 were women. Subjects with POAG (59.85 +/- 10.43 years) were older (P < 0.001) than the study population (53.78 +/- 10.71 years). In only one (1.5%) person was POAG diagnosed before the study. Two (3.12%) subjects were blind due to POAG; 21 (32.81%) subjects had a presenting IOP >21 mm Hg, and 43 (67.19%) had an IOP <21 mm Hg. The mean central corneal thickness in subjects with POAG (502.82 +/- 35.29 microm) was not different from that of the normal study population (505.93 +/- 31.11 microm). No association was found with diabetes mellitus, systemic hypertension, gender, and myopia. Increasing IOP (per mm Hg) was associated with the disease (OR 1.12; 95% CI, 1.08-1.16). The odds for POAG increased with advancing age after adjustment for gender. CONCLUSIONS: The prevalence of POAG in this population was 1.62%. The prevalence increased with age, and 98.5% were not aware of the disease.

Diabetic retinopathy screening model for rural population: awareness and screening methodology.

CONTEXT: Worldwide, the prevalence of diabetic retinopathy is increasing at an alarming rate. WHO has predicted that in India the number of adults with diabetes will be the highest in the world: from 19 million in 1995 to 80 million in 2030. Although originally thought to be a disease of an urban population, the prevalence of diabetes mellitus is increasing in rural areas as well. The socioeconomic burden resulting from visual impairment or blindness caused by diabetic retinopathy, particularly in the working age group, is a serious concern. ISSUE: In order to combat diabetic retinopathy related blindness, Sankara Nethralaya, the premier eye institute of India, in collaboration with the Lions Clubs International Foundation (LCIF) and the RD Tata Trust, Mumbai, India launched a major diabetic retinopathy screening program in the rural community of South India. The objectives were to create awareness among the rural population of diabetic retinopathy with emphasis on early detection, to conduct diabetes and diabetic retinopathy screening camps, and to bring to the base hospital patients who have sight-threatening diabetic retinopathy, for ancillary investigations such as fluorescein angiography, ultrasound and to perform laser photocoagulation or vitreous surgery, or both. Other objectives included training general ophthalmologists and general physicians in order to develop an integrated diabetic retinopathy model. To address the question as to why certain individuals run the risk of developing sight threatening diabetic retinopathy, biochemical and genetic factors were also studied. The program was launched in June 2003 and 3 rural districts have been screened. To the time of writing, 128 screening camps had been organized, 103 awareness meetings conducted, 23 ophthalmologists trained and 43 general physicians attended the continuing medical education program on diabetic retinopathy. LESSONS: The key elements in the successful implementation of this program have been a team approach, involvement of community leaders and voluntary organizations, and support of the district and state administrators.

Sankara Nethralaya-Diabetic Retinopathy Epidemiology and Molecular Genetic Study (SN-DREAMS 1): study design and research methodology.

PURPOSE: To describe the methodology of the Sankara Nethralaya-Diabetic Retinopathy Epidemiology and Molecular Genetic Study (SN-DREAMS 1), an ongoing population-based study to estimate the prevalence of diabetes and diabetic retinopathy in urban Chennai, Tamil Nadu, South India, and also to elucidate the clinical, anthropometric, biochemical and genetic risk factors associated with diabetic retinopathy. METHODS: In this ongoing study, we anticipate recruiting a total of 5830 participants. Eligible patients, over the age of 40 years, are enumerated using the multistage random sampling method. Demographic data, socioeconomic status, physical activity, risk of sleep apnea, dietary habits, and anthropometric measurements are collected. A detailed medical and ocular history and a comprehensive eye examination, including stereo fundus photographs, are taken at the base hospital. Biochemical investigations (total serum cholesterol, high-density lipoproteins, serum triglycerides, hemoglobin, glycosylated hemoglobin HbA1c) and genetic studies of eligible subjects are conducted. A computerized database is created for the records. CONCLUSION: The study is expected to result in an estimate of the prevalence of diabetes and diabetic retinopathy and a better understanding of biochemical and genetic risk factors associated with diabetic retinopathy in an urban South Indian population. Worldwide, the prevalence of diabetes mellitus, in particular type II diabetes, is rising at an alarming rate. The World Health Organization (WHO) and International Diabetes Federation (IDF) have predicted that the number of cases of adult-onset diabetes would more than double by 2030 from the present level of 171 million to 366 million-an increase of 214%.1 In developed countries, this increase in diabetic population would be around 42% and in developing countries, particularly in India, it is even higher; i.e. 150%.1 In India, the prevalence of diabetes mellitus in the urban population is around 12.1%, as reported by the national urban diabetes study2 conducted in six major cities. Studies have shown the prevalence of diabetes to be higher among the high-income groups (25.5%) as compared to low-income groups (12.6%).3,4,5 The assessment of socioeconomic status was based on income,6, 7 education,2, 7 occupation2 or caste6-which are not representative of the actual socioeconomic status. In the present study, however, the sample was stratified on socioeconomic scoring. This scoring was calculated on the basis of several parameters such as the residence being rented or owned, the number of rooms in the house, the highest educational status, the highest salary, the highest occupation, material possessions (cycle, TV, audio, car, etc.) and house/land value. To the best of our knowledge, this kind of comprehensive socioeconomic scoring has not been done before for prevalence studies on diabetic retinopathy in the general population.

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 [corrected] (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.

Karyotyping in retinoblastoma--a statistical approach.

PURPOSE: Karyotype analysis in hereditary retinoblastoma is considered to be of marginal value in risk prediction due to uncertainties in the assessment of 13q14 deletions. However, it is a low cost genetic test for retinoblastoma in developing countries. In the present study, the results of karyotype analysis were refined by a statistical method to overcome limitations. METHODS: Karyotype analysis was performed by trypsin-Giemsa banding and naked eye karyotyping for 33 bilateral, 25 unilateral and one regressed retinoblastoma patients. The percentage of metaphases with 13q14 deletions in each case was plotted on a scatter diagram. Normalization of the data was achieved by log transformation and the results were statistically analyzed by one-sample 't' test using SPSS version 9.0. RESULTS: Seven samples had 13q14 deletion percentages above the cutoff value. One-sample 't' test showed significance (p< 0.001). By this method, two unilateral and five bilateral patients had 13q14 deletions, constituting 11.8 % of cases. CONCLUSION: For accuracy, statistical analysis should be considered as an adjunct in karyotyping.

Prevalence of refractive errors in a rural South Indian population.

PURPOSE: To report the prevalence of refractive errors in a rural south Indian population. METHODS: Four thousand eight hundred subjects (age, >39 years) from rural south India were enumerated for a population-based study. All participants underwent complete ophthalmic evaluation. Subjects who were phakic in the right eye with best corrected visual acuity of 20/40 or better were included for analysis. Association of refractive errors with age, sex, cataract, and diabetes mellitus were analyzed. RESULTS: Of the 3924 responders, 2508 were eligible. The unadjusted prevalence of emmetropia (spherical equivalent [SE], -0.50 to +0.50 diopter sphere [DS]), myopia (SE < -0.50 DS), high myopia (SE < -5.00 DS), and hyperopia (SE > 0.50 DS) were 50.60%, 26.99%, 3.71%, and 18.70% and age and gender adjusted for the rural Tamil Nadu population were 46.77%, 30.97%, 4.32%, and 17.94%, respectively. The prevalence of emmetropia decreased significantly with age (P < 0.0001), and the prevalence of myopia and high myopia increased significantly with age (P < 0.001) and were significantly associated with nuclear sclerosis (P < 0.001). The prevalence of hyperopia increased until 60 years of age and then decreased. Hyperopia was more common among women than men (P < 0.001) and was negatively associated with nuclear sclerosis (P < 0.001) and positively with diabetes mellitus (P = 0.008). Of the participants with astigmatism (cylindrical error greater than 0.50 DC), 9.80% had with-the-rule (WTR) and 77.44% against-the-rule (ATR) astigmatism. The prevalence of WTR and ATR astigmatism significantly decreased (P < 0.001) and increased (P = 0.006) with age, respectively. CONCLUSIONS: The pattern of refractive errors in this rural south Indian population is similar to those reported in other tropical regions of the world.

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.