Acanthamoeba keratitis - A six year epidemiological review from a tertiary care eye hospital in South India.

PURPOSE: This study analyses the prevalence, demography, predisposing factors and seasonal variation of Acanthamoeba keratitis. METHODS: A retrospective review of all cases presenting with keratitis at the cornea clinic, Aravind Eye Hospital, Coimbatore, from August 1997 to July 2003, was done for screening patients with a provisional diagnosis of Acanthamoeba keratitis. Their records were further analyzed for microbiological details. Cases with culture proven Acanthamoeba keratitis were included for epidemiological analysis. RESULTS: From a total of 4519 patients who attended cornea clinic 32 (33 eyes) patients were confirmed to be positive for Acanthamoeba keratitis. Twenty cases (62.5%) were males. Majority (18; 54.2%) of the Acanthamoeba keratitis eyes reported corneal trauma by solid objects. No peak period was observed in a year, as the number of cases was almost uniform in all months. CONCLUSION: This study indicates the increasing prevalence of Acanthamoeba keratitis among non-contact lens users in this region during the 6-year period.

Estimation of blindness in India from 2000 through 2020: implications for the blindness control policy.

BACKGROUND: To eliminate avoidable blindness in India, appropriate national planning is necessary, which should be based on current and reliable data. A national survey done in 1986-89 reported that 1.5% of the Indian population (12 million people) was blind with a presenting visual acuity of < 6/60 in the better eye. The original goal of the National Programme for Control of Blindness was to reduce this prevalence to 0.3% by 2000. We have recently reported the prevalence of blindness in the population of Andhra Pradesh to be 1.66% with a presenting visual acuity of < 6/60 in the better eye as the sole criterion and 1.84% with a presenting visual acuity of < 6/60 orcentral visual field < 20 degrees in the better eye. We used these population-based data to estimate blindness in India in 2000 and project the possible scenarios of blindness through 2020 with different emphases of the blindness control policy in India. METHODS: Recent population-based data on the age-, sex- and cause-specific blindness rates from the Andhra Pradesh Eye Disease Study for the entire age range were applied to the population distribution of India to estimate the number of blind persons in 2000. The age-, sex- and cause-specific rates of blindness were then applied to the estimated age, sex and urban-rural population distribution of India in 2010 and 2020 to project the number of persons blind (from various causes) and the blind person-years that would be suffered under varying degrees of emphasis in the policy to control blindness due to particular diseases. For these projections, blindness was defined as a presenting distance visual acuity of < 6/60 or central visual field < 200 in the better eye. RESULTS: The number of blind persons in India in 2000 was estimated to be 18.7 million (95% confidence interval [CI]: 15.2-22.3), of which 9.5 million were cataract-related and 3 million refractive error-related. If there is no change in the current trend of blindness, the number of blind persons in India would increase to 24.1 million (95% CI: 19.7-28.4) in 2010, and to 31.6 million (95% Cl: 26.4-36.9) in 2020. If effective strategies are put in place to eliminate 95% of blindness due to cataract by 2020, blindness in 15.6 million persons would be prevented who would otherwise be blind in 2020 if the current trend continues, and 78 million blind person-years would be prevented in these persons. Similarly, if effective strategies are also implemented to eliminate 95% of the refractive error blindness by 2020, another 4.2 million persons would be prevented from being blind in 2020, and 82 million blind person-years would be prevented. In addition, if strategies to prevent 90% of the preventable blindness due to corneal disease and glaucoma are successful by 2020, blindness in an additional 3.6 million persons in 2020 and 29 million blind person-years would be prevented. CONCLUSION: The planning of blindness control in India should take into account recent population-based data for the entire age range, which suggest that the number of blind persons in India is currently over 18 million. This estimate is 50% more than the figure of 12 million from a decade ago that is still quoted widely in the blindness control policy documents. If avoidable blindness is to be substantially reduced in India by 2020, effective strategies against blindness due to cataract and refractive error are needed urgently as both these conditions are relatively easy to treat. Also, strategies against preventable corneal and glaucoma blindness need to be strengthened soon for them to show an impact over the next two decades.

Planimetric optic disc parameters in normal eyes: a population-based study in South India.

PURPOSE: To study the optic disc parameters of normal eyes in a population-based south Indian study. METHODS: One hundred and fifty three subjects from a population-based sample of 1060 included in the Andhra Pradesh Eye Disease Survey (APEDS) were enrolled in the optic disc study. The male-female ratio, the refractive error and distribution of other ocular parameters in the disc study subjects and the APEDS were not significantly different. Magnification corrected morphometry of optic disc photographs obtained by Zeiss telocentric fundus camera was carried out in one randomly chosen eye of each of these 143 subjects. RESULTS: The mean optic disc parameters with the 95% confidence intervals for the distribution were: disc area 3.37 mm2 (2.04 - 4.7), vertical disc diameter 2.12 mm (1.67 - 2.57), vertical cup to disc ratio 0.37 (0.19 -0.55) and neuroretinal rim area 2.8 mm2 (1.76 - 3.84). The disc area, the vertical cup to disc ratio and the rim area showed a normal distribution. The cup to disc ratio correlated with the vertical disc diameter but the association was not strong. CONCLUSION: The disc area, the vertical cup to disc ratio and the neuroretinal rim area are normally distributed in the South Indian population. The normal optic disc parameters would form a basis for future comparisons in different forms of glaucoma.

Sample size for ophthalmology studies.

Knowledge and the usage of actual sample size formulae are a necessity as validity of the inferences from research studies is often dependent on this. This paper explains how sample sizes are calculated. The concept of sampling variation is explained to emphasize the need for its proper calculation. Sample size formulae are explained with examples to provide researchers with a means of calculating the sample sizes for the commonly used study designs. Ophthalmic data are used as examples. It is perceived that this will improve the quality of inferences drawn from ophthalmic research studies.