Faculty Bibliography

PURPOSE: To determine the extent of rod and cone photoreceptor dysfunction in patients with cone dystrophy using psychophysical and electrophysiological tests. METHODS: Ten patients with cone dystrophy participated. Rod and cone system psychophysical thresholds were measured as a function of retinal eccentricity. Bright-flash full-field electroretinograms were obtained under dark-adapted (rod-mediated) and light-adapted (cone-mediated) conditions. The a-wave data were fitted with a model based on photopigment transduction to obtain values for log Rmax (maximum response) and log S (sensitivity). b-Wave parameters were also examined by fitting a nonlinear, saturating function (the Naka-Rushton equation) to the rod-mediated responses. Oscillatory potentials were measured to the cone-mediated high-intensity flashes. RESULTS: On average, the rod-mediated psychophysical thresholds were elevated by 0.5 log unit. These threshold elevations did not differ significantly with retinal eccentricity. In contrast, cone-mediated psychophysical thresholds were elevated up to 3.0 log units. Threshold elevation was greatest in the central retinal locations. For rod-mediated conditions, the a-wave Rmax parameter was significantly reduced in three patients; the a-wave log S parameter was within normal limits. The rod-mediated b-wave Rmax parameter was reduced in six patients; log k was abnormal in one patient. For cone-mediated conditions, the a-wave Rmax parameter was reduced in six patients and the a-wave log S parameter was reduced in two patients. The cone system oscillatory potentials were abnormal in nine patients. CONCLUSIONS: Patients with cone dystrophy show different patterns of psychophysical rod versus cone system sensitivity losses with retinal eccentricity. The full-field electrophysiological data indicate that most of the patients had abnormal cone photoreceptor function. Some patients also showed rod photoreceptor abnormalities. The rod system changes were smaller than the cone system changes

Multidimensional psychophysical and electrophysical maps of the central retina are essential for assessing the functioning of the diseased retina. In this study, grating acuity, contrast sensitivity, duration for letter identification, multifocal electroretinograms, and Humphrey visual field thresholds were measured at equivalent positions throughout the central 20 degrees . We found that the rates of sensitivity loss were not equivalent for all psychophysical measures. The rate of loss in the duration required for letter identification as a function of eccentricity was the steepest, followed by acuity and contrast sensitivity. The rate of loss in luminance sensitivity as measured in the Humphrey visual field was the shallowest. The pattern of losses also varied across meridians. Specifically, the rate of loss as a function of eccentricity was highest in the vertical meridian and lowest in the horizontal meridian. These maps and the correlations among measures as a function of retinal position serve as a baseline so that we can examine disease effects throughout the retina. In addition, the development of vision rehabilitation programs focused on eccentric viewing training should consider the differential sensitivities of the peripheral retina

PURPOSE: A body of clinical and laboratory evidence suggests that tinted spectacle lenses may have an effect on visual performance. The aim of this study was to quantify the effects of spectacle lens tint on the visual performance of 25 subjects with cataracts. METHODS: Cataracts were scored based on best-corrected acuity and by comparison with the Lens Opacity Classification System (LOCS III) plates. Visual performance was assessed by measuring contrast sensitivity with and without glare (Morphonome software version 4.0). The effect of gray, brown, yellow, green and purple tinting was evaluated. RESULTS: All subjects demonstrated an increase in contrast thresholds under glare conditions regardless of lens tint. However, brown and yellow lens tints resulted in the least amount of contrast threshold increase. Gray lens tint resulted in the largest contrast threshold increase. CONCLUSIONS: Individuals with lenticular changes may benefit from brown or yellow spectacle lenses under glare conditions