A Prospective Study of Rod and Cone Function in Patients With Dominantly Inherited, Progressive Cone Dystrophy

Abstract

Abstract: : Purpose:To compare long–term changes in local and full–field measures of visual function in affected members of a family with dominantly inherited cone dystrophy. Methods:Six affected members from three generations of a family with progressive cone dystrophy were examined prospectively. Each subject returned for a minimum of four visits over a period of twenty–five years. The following measures were obtained on repeated visits: indirect ophthalmoscopy, fundus photographs, visual acuity, color vision, dark–adaptation curves, two–color dark–adapted visual fields, local ERGs, and full–field ERGs. Results:For 5 patients, there were no disease–related fundus changes, 1 patient showed increased atrophy of the macular area over the years of study. On average, visual acuity decreased at a rate of 0.2 logMAR/decade (2 Snellen lines/decade). Color vision (D–15 and FM 100–hue tests) changed from normal to tritan and then to scotopic deficits with poor hue discrimination. Full–field scotopic ERGs were normal or near normal initially; photopic ERGs and multifocal ERGs were non–measurable or greatly reduced in amplitude and delayed even in patients with good visual acuity. The amplitudes of the rod– and cone–system ERGs decreased during the study; however, the rate of change was 3 times greater for the cone–system than for the rod–system responses. The cone portion of the dark–adaptation curves were greatly elevated or non–measurable; the rod portion time course was abnormal for three patients and final rod thresholds were elevated by 0.3 – 1.0 log–units. The two–color dark–adapted visual fields showed relatively little change over time. Conclusions:Over the follow–up period, all patients showed consistent deterioration in cone–system electrophysiological and psychophysical measures. The rod–system ERGs also showed progressive deterioration over the course of the study, but at a slower rate than the cone system. The rod–system psychophysical measures showed little change over the follow–up period. These results differ from the pattern seen in patients with typical cone–rod or rod–cone degenerative diseases.

Keywords: retinal degenerations: hereditary • electroretinography: clinical • perimetry