The Effect of Over Minus Prescription on Negative and Positive Fusional Vergence and Amplitude of Accommodation After Watching Video at Six Meters

Abstract

Background The purpose of the study was to compare the effects of a -1.00 Dioptre Sphere over minus prescription on negative fusional vergence and positive fusional vergence as well as the amplitude of accommodation in myopic individuals after watching a video at 6 meters.Aim To assess the effect of over-minus lens on the amplitude of accommodation and fusional vergence pre and post-video watching.Methods The study included 30 participants aged between 18 to 25 years who did not have any systemic or ocular-related issues. During the study the participants were given an over-correction of -1.00DS over their existing spectacle correction. They were then instructed to watch a video at a distance of 6 meters for 15 minutes. The amplitude of accommodation as well as negative and positive fusional vergence were measured before and after the 15-minute video-watching session.Results The study results indicate that there was a statistically significant change in the amplitude of accommodation in the right eye when using an over-correction of -1.00DS. However there was no statistically significant change in the fusional vergence with the minus over-correction.Conclusion It is possible that the reduction in the accommodation system observed in the study was caused by wearing the divergence lens which placed the image behind the retina resulting in retinal blur. Prolonged wear of over-minus lenses could also lead to visual fatigue which can disrupt the eye-focusing system. Therefore while prescribing a corrective lens it should be monitored carefully.