The effect of sunglass filters on contrast sensitivity, monocular eye closure, and blinking rate in people with intermittent exotropia.

CLINICAL RELEVANCE Transient monocular eye closure and photosensitivity under bright light have been reported in people with intermittent exotropia (IXT). The exact mechanism of these symptoms has not been established. BACKGROUND This study examines the effect of sunglass filters on contrast sensitivity (CS), transient monocular eye closure, and blinking rate under bright light in people with IXT. METHODS Forty participants with IXT and complaints of photosensitivity were included in the study. The binocular CS test was performed under mesopic and photopic conditions with and without glare, and with and without two filters with different grades of light transmission (filter 1: 44-80%; filter 2: 20-43% light transmittance). The effect of two filters on transient eye closure, contrast sensitivity, and blinking rate was assessed under bright light. Also, participants were divided into 3 groups based on their degree of control of fusion (good, fair, and poor control). RESULTS The mean age of the participants was 12.0 years ± 8.0 (standard deviation) (range: 7-40 years). There was no significant difference between the age (p = 0.139), stereopsis (p = 0.134), as well as the near and far degree of deviation (p = 0.516, and p = 0.237) between the three groups of fusion control. Under mesopic conditions with glare, mean binocular CS was significantly higher with filters (p < 0.001). Without filters, 57.5% of the participants exhibited monocular eye closure under a photopic setting with additional glare. No participant showed eye closure using filter 2. People in the poor control group showed exodeviation before monocular eye closure (62.5% without filter and 12.5% with filter 1, p = 0.01). The blinking rate decreased from 36.0 ± 4.0 blinks per minute without filter to 21.0 ± 3.0 using filter 1, and 20.0 ± 3.0 with filter 2. CONCLUSION In people with IXT, wearing sunglass filters of different transmittance reduces monocular eye closure and blinking rate under bright light. To improve these symptoms, sunglasses can be considered for IXT.