A Clinical Study of Subtype-based Prevalence of Dry Eye

Dry Eye is a multifactorial disease of the tearfilm and the ocular surface which may be due to reduced tear production or excessive tear evaporation resulting in discomfort, visual disturbance, and tear film instability with a potential damage to the ocular surface. Various population-based studies have been done to find out the prevalence and the magnitude of the problem. Women Health Study reported prevalence of 7.8% after screening 36995 subjects above 49 years by interview. The prevalence reported by Blue Mountain Study was 15.3% .The Beaver Dam Study and Shiphai Eye studies are other studies reporting prevalence of 14.5% and 33.7% respectively. McMonnies questionnaire is a widely used screening instrument for Dry-Eye syndromes with sensitivity reportedly varying between 87% and 98% and specificity between 87% and 97%. Prevalence studies use McMonnie's questionnaire for screening individuals for Dry Eye, whereafter tests like Schirmer's test, Tear Film Break Up Time test, Rose Bengal test, Lissamine Green test and Meibomian Gland Dysfunction test are useful for further evaluation. While these tests help to differentiate the subtypes of Dry Eye such as Lipid Anomaly Dry Eye, Aqueous Tear Deficiency and Mucin Layer Deficiency, however, their sensitivity and specificity has not been widely studied. Additionally, very few studies have reported the prevalence of the various subtypes of Dry Eye.

To determine the subtype-based prevalence of Dry Eye, to study the specificity and sensitivity of clinical tests for Dry Eye and to correlate McMonnies questionnaire with Dry Eye tests results.

A prospective, cross-sectional, observational study, duly approved by the Institutional Ethics Committee, was conducted from October 2010 to April 2012. A total of 4750 subjects above 18 yrs of age were screened by the McMonnies questionnaire. Respondents having a score greater than 14.5 were subjected to clinical Dry Eye tests. The data obtained was analyzed using chi-square test. p value < 0.005 was considered statistically significant.The specificity and sensitivity of each clinical test was calculated using Schirmer's test as gold standard.

The prevalence of Dry Eye was 15.4%, with a female preponderance (p = 0.01) and a significant increase with age above 60 years was noted (p<0.0001). Tear Film Break Up Time was the most reliable test with a good sensitivity (68.85%) and specificity (78.32%). Lipid Anomaly Dry Eye was the most prevalent (14.48%) followed by Aqueous Tear Deficiency (13.36%) and Mucin Layer Deficiency (3.51%). A positive correlation between McMonnies score and severity of Dry Eye was seen.

This study suggests that Lipid Layer Anomaly is the most prevalent subtype in Dry Eye. Tear Film Break Up Time test is the most likely test to diagnose mild Dry Eye. McMonies Questionnaire can be effectively used for screening of a large population. Tear Film Break Up Time was found to have better sensitivity as well as specificity than other tests used for diagnosing Dry Eye.