DOI: 10.5061/dryad.5qfttdz19
title: Association of cataract and sun exposure in geographically diverse populations of India: the case study. first report of the ICMR-EYE SEE study group

description: Purpose: To determine the prevalence of cataract and its association with
 sun exposure and other environmental risk factors in three different
 geographically diverse populations of India. Design: Population based
 cross sectional study during 2010-2016 Participants: People aged &gt;
 40 years residing in randomly sampled villages were enumerated (12021) and
 9735 (81%) underwent ophthalmic evaluation from plains, hilly and coastal
 regions (3595, 3231, 2909 respectively) Methods: A detailed
 questionnaire-based interview about outdoor activity in present, past and
 remote past, usage of sun protective measures, exposure to smoke, and
 detailed ophthalmic examination including assessment of uncorrected and
 best corrected visual acuity, measurement of intraocular pressure, slit
 lamp examination, lens opacities categorization using LOCS III and
 posterior segment evaluation was done. Lifetime effective sun exposure was
 calculated using Melbourne formula and expressed as quantiles. These were
 supplemented with physical environmental measurements. Main outcome
 measures: Lifetime sun exposure hours, smoking, indoor kitchen smoke
 exposure and their association with cataract and subtypes. Prevalence of
 cataract calculated based on lens opacities or evidence of cataract
 surgery. Results: Cataract was identified in 3231 (33.3%) participants.
 Prevalence of cataract in males (32.3%) and females (34.1%) was similar.
 Nuclear cataract was the commonest sub-type identified in 94.7% of
 affected eyes. Sun exposure had a significant association with cataract
 with odds ratio (OR) increasing from 1.6 (95% Confidence Intervals [CI]:
 1.4, 1.9) in 3rd quantile, to 2.6 (CI: 2.2, 3.1) in 4th quantile and 9.4
 (CI: 7.9, 11.2) in 5th quantile (p&lt;0.0001). Cataract also showed a
 significant association with smoking (OR: 1.4, CI: 1.2, 1.6) and indoor
 kitchen smoke exposure (OR: 1.2, CI: 1.0-1.4). Nuclear cataract showed a
 positive association with increasing sun exposure in 3rd (β coefficient
 0.5, CI:0.2-0.7), 4th (β: 0.9, CI: 0.7-1.1) and 5th (β: 2.1, CI:1.8-2.4)
 quantiles of sun exposure, smoking (β: 0.4, CI: 0.2-0.6) and indoor
 kitchen smoke exposure (β: 0.3, CI: 01-0.5) while cortical cataract showed
 a positive association with sun exposure only in 5th quantile (β: 2.6,
 CI:1.0-4.2). Posterior subcapsular cataract was not associated with any of
 the risk factors. Conclusion: Cataract is associated with increasing level
 of sun exposure, smoking and exposure to indoor kitchen smoke.
description: All analysis was doen using Stata Version 13
 Participants with incomplete information on sun exposure or
 ocular examination were excluded. All study
 participants were distributed across quintiles, based lifetime effective
 sun exposure. The prevalence of cataract was assessed
 among persons whose clinical lens evaluation was complete.
 Prevalence of specific subtype of cataract was calculated among
 participants whose LOCS III evaluation in either eye was done.
 Participants with traumatic or developmental cataracts were
 excluded. The combination patterns of subtypes of
 cataracts in the LOCS III assessed eyes were tabulated.
 In case one eye had cataract while other eye was pseudophakic or
 apahakic, we classified the participant based on the cataractous
 eye. Multivariable logistic regression analysis was
 done to estimate the association of sun exposure, smoking, and gender and
 other risk factors with any cataract. Analysis were
 repeated for each site and for pooled data. Patients
 with pure cortical, nuclear and PSC based on LOCS III score were
 identified and the association with sun exposure and other risk factors
 was evaluated using multinomial logistic regression analysis, keeping
 person with both eyes normal as controls.
description: The main person-wise data file  is
 "UVR-cataract-analysis.dta" and to reproduce the analysis, use
 the "UVR-cataract-analysis.do" file in Stata version 13. The
 "UVR-cataract-analysis - Codebook.pdf" file lists the variables
 in the dataset. Its also describes the number of missing values in the
 dataset for various variables.  The
 "LOCSeyePattern.dta" file is a longform data of each eye, where
 eye = 1 means right eye and eye=2 means left eye. The "LOCSeyePattern
 - Codebook.pdf" describes the variables used in this
 dataset. The "UVR-cataract-analysis.do" file
 runs the analysis and saves the results as "Results.pdf" and
 "<em>date</em>_combinedUVR40+_6.smcl" files. As an
 intermediate step, "combinedUVR40+_7.dta" and
 "UVR-cataract-analysis_7.dta" files are generaed and these may
 be ignored. The Key Variables are - 
 unique_id - person unique ID
 anyCataract - Person with any eye having cataract - prevalence
 of any cataract cort_prev nuc_prev psc_prev -
 prevalence of any specific type of cataract
 cort_assoc nuc_assoc psc_assoc pure_assoc - Distribution of pure
 sub-types of cataracts age - Age of participant -
 continuous gender - Gender
 educat2 - Educational status workTypePrCat
 - Occupation (Present smoke20 - Smoking
 indoor16_kitchen - Indoor Smoke tExposure -
 Lifetime cumulative effective sun exposure - continuous
 tExposureQuantilesAll  - Lifetime cumulative effective sun
 exposure expressed as quintiles
 study_location  sugar200 -
 Diabetes pvaBe - Vision Status based on presenting
 visual acuity in better eye bvaBe - Vision Status
 based on best corrected visual acuity in better eye
 beOp - Both eyes operated for cataract
 oneEyeOp - One Eye operated for cataract
 locsRe*, locsLe* - LOCS III grading results of eirther eye for
 cortical opacity, nuclear opacity, nuclear opalescence and PSC