Eyelid Squint Response to Asthenopia-Inducing Conditions

Abstract

Refractive error and glare, which reduce image quality and benefit from eyelid squint, caused increased EMG power, eyelid squint response and increased blink rate. Low contrast and small font, which reduce image quality but do not benefit from eyelid squint, resulted in increased EMG power without changes in aperture size and reduced blink rate (for low contrast). Accommodative and convergence stress (in subjects with normal accommodative and vergence abilities) did not cause changes in EMG power, aperture size or blink rate. These results suggest that contraction of the orbicularis oculi is a part of the asthenopia mechanism related to compromised image quality.