Can Down-gaze During Near Work Cause Peripheral Deprivation in Asian Eyes?

Abstract

Purpose 

We hypothesize that the typically narrower palpebral apertures of East Asian eyes in combination with the narrowing of this aperture during down-gaze combine to reduce light levels and image contrast in the inferior retina during near work, thus creating peripheral deprivation in these eyes that could generate deprivation myopia in children culturally encouraged to perform near work.

Methods 

We photographed the right eyes of 53 Chinese children during down-gaze (from 10 to 40 degrees) from the fixation point and the primary gaze position. From these images, we determined the size and shape of the effective foveal and superior field entrance pupil at different down-gaze angles. By using an eye model with typical levels of off-axis higher-order aberrations, we quantified the impact of eyelid and eyelash vignetting of the pupil on both retinal illuminance and image quality using Visual Strehl Ratio (VSOTF), and the non-visually weighted Strehl Ratio (SROTF).

Results 

The effective aperture for the superior visual field is vignetted during down-gaze by lids and lashes, producing reductions in retinal illuminance of 30% and >60% at 20 and 40 degrees, respectively. However, the aperture vignetting effect on peripheral image modulation is small, with neural and aberration changes dominating image quality in the superior field during down-gaze.

Conclusions 

Occlusion of the pupil by eyelid and eyelashes during down-gaze is unlikely to produce significant superior field deprivation in East Asian eyes.