Contrast sensitivity in the ‘good eye’ of adult patients with severe impairment in the other eye

Abstract

It is widely accepted that monocular deprivation results in improved visual performance in the non-pathological eye. The current study investigates the effect of deprivation due to severe impairment in one eye during late childhood or adulthood, on the spatial performance of the fellow 'good' eye. Twenty patients (age: 29 ± 9 years) with severe visual impairment in one eye (visual acuity equal or worse than count fingers at 1 m), for a period longer than 2 years, participated in the study. Only patients with an age less than 50 years and monocular deprivation onset greater than 9 years were included. On the basis of the time of deprivation the patients were categorised into two subgroups: (i) long-past deprivation (N = 8, age 28 ± 8 years, 9-20 years of deprivation) and recent deprivation (N = 12, age 30 ± 11 years, 2-4 years of deprivation). Eighteen more participants (age: 28 ± 5 years) with normal binocular vision served as the control group. Best-corrected contrast sensitivity was evaluated using reversing (2 Hz) vertical sinusoidal gratings. Seven spatial frequencies (1, 2, 4, 8, 12, 16 and 24 c/deg) were tested. Performance of the control group was tested both monocularly (dominant eye) and binocularly. In normal subjects, binocular viewing improved contrast sensitivity on average by 4.2 dB (corresponding to a 70% improvement in contrast threshold) compared to monocular recordings. Average contrast sensitivity in subjects with impaired vision in one eye was found to be higher by 5.0 dB (corresponding to an 83% improvement in contrast threshold) compared with the dominant eye of the control group. The increase in sensitivity was independent of spatial frequency. No differences were observed between the two subgroups with recent and long-past deprivation. Notable improvement in contrast sensitivity was found in the non-pathological eye of patients with severe impairment in the other eye at an age after the "critical" period of visual development. These findings are consistent with growing evidence supporting functional changes as a result of altered experience or injury in the adult vision system.