Faculty Bibliography

The purpose of this study is to test the hypothesis that glaucoma leads to selective deficits in parallel pathways or channels. Sweep VEPs were obtained to isolated-check stimuli that were modulated sinusoidally in either isoluminant chromatic contrast or in positive and negative luminance contrast. Response functions were obtained from 14 control subjects, 15 patients with open-angle glaucoma, and seven glaucoma suspects. For all three groups of subjects we found characteristic differences between the VEP response functions to isoluminant chromatic contrast stimuli and to luminance contrast stimuli. The isoluminant chromatic stimulus conditions appeared to favor activity of the P-pathway, whereas the luminance contrast stimuli at low depths of modulation favored M-pathway activity. VEP responses for patients with OAG were significantly reduced for chromatic contrast and luminance contrast conditions, whereas VEP responses for glaucoma suspects were significantly reduced only for the 15-Hz positive luminance contrast condition. Our results suggest that both M- and P-pathways are affected by glaucoma

To assess local retinal function in patients with retinitis pigmentosa (RP), multi-focal ERGs and local thresholds (static visual fields) were obtained on eight RP patients with visual acuities of 20/25 or better. All eight patients showed multi-focal responses with normal timing within the central 5 deg. However, there were few responses with normal timing in the areas outside the central 7.5 deg, except in the case of the only patient with a 30 Hz full-field response with normal timing. Since full-field ERGs are dominated by responses from the periphery, this finding supplies a foundation for the commonly observed delays in the full-field cone ERGs of patients with RP. With respect to amplitude, only two patients showed multi-focal responses with near normal amplitudes anywhere in the field. The loss of amplitude at any point was not a good predictor of visual sensitivity in the Humphrey visual field. On the other hand, all areas with normal timing had near normal sensitivity. Timing changes appear to be an early indication of local retinal damage to the cone system. Nearly all areas with sensitivity losses greater than 0.5 log unit, and some areas with near normal sensitivity, showed significantly delayed multi-focal ERGs. Finally areas with extreme sensitivity loss show multi-focal responses with a wide range of amplitudes and implicit times across patients, suggesting different mechanisms of disease action in different patients

PURPOSE: To determine whether the rod and cone photoreceptors are affected in patients with diabetic retinopathy. METHODS: Twelve patients with diabetes and varying levels of retinopathy and nine age-similar control observers participated in this study. Two-color (500 versus 650 nm) dark-adapted thresholds were measured as a function of retinal eccentricity. Full-field flash electroretinograms were obtained using brief, high-intensity flashes. Dark-adapted rod-isolated (Wratten 47B filter) and light-adapted cone-isolated (Wratten 26 filter) electroretinographic responses were measured as a function of flash intensity. The a-wave data were fitted with a model based on photopigment transduction to obtain values for the parameters of Rmax (the maximal response) and log S (sensitivity). Standard clinical 30-Hz flicker electroretinographic responses were also measured. RESULTS: Psychophysically measured dark-adapted thresholds were elevated primarily at eccentricities of 5 degrees and 10 degrees from the fovea. Analysis of rod and cone a-wave data showed that Rmax was normal in most of the patients, but log S was reduced. Analysis of b-wave and oscillatory potential parameters showed rod and cone postreceptoral abnormalities, including changes in the rod-isolated semisaturation constant (log k), cone-mediated 30-Hz flicker, and cone-isolated oscillatory potentials. The electrophysiological results were not significantly correlated with blood glucose or glycosylated hemoglobin level. CONCLUSIONS: The results provide evidence for rod and cone receptoral and postreceptoral deficits in patients with diabetic retinopathy. The photoreceptor changes are primarily in the log S (sensitivity) parameter and are attributed to transduction abnormalities

The multi-input technique of Sutter and Tran (1992) yields multiple focal ERGs. The purpose here was to compare the components of this multifocal ERG to the components of the standard, full-field ERG. To record multifocal ERGs, an array of 103 hexagons was displayed on a monitor. Full-field (Ganzfeld) ERGs were elicited by flashes presented upon steady background fields. The latencies of two prominent subcomponents of the full-field ERG were altered by varying the intensity of the incremental flash or the intensity of the background field. By showing that similar manipulations of the multi-input parameters produce similar changes in latency, we were able to relate the components of the multifocal ERG to the components of the full-field ERG. The biphasic responses of the multifocal ERG appear to be generated by the same cells generating the a-wave and positive peaks of the full-field cone ERG

The purpose of this study was to determine the extent of peripheral visual deficits in patients with early age-related macular degeneration (ARMD) using electrophysiological and psychophysical techniques. Dark-adaptation curves, electro-oculograms (EOGs), and electroretinograms (ERGs) were obtained from patients with early ARMD and from normally sighted control subjects. The control subjects' data were used to calculate age-dependent 95% confidence intervals for each measure of visual function. For the control subjects, performance on all our measures of visual function decreased with age. For the patients with early ARMD, the cone system absolute thresholds, EOG ratios, and cone-dominated ERG amplitudes and implicit times were within the range of normal age-related changes. Rod system absolute thresholds, cone-rod break times, and rod-dominated electroretinographic measures were abnormal in some patients. These results suggest that when the effects of aging are taken into account, some patients classified as early ARMD may not show significant changes in peripheral retinal function with standard clinical tests

The purpose of the study was to test the hypothesis that the retinae of patients with enhanced S cone syndrome (ESCS) have more S cones than the normal retina and these cones have replaced some of the L and M cones. Standard and spectral full-field electroretinograms, measurements of L, M, and S cone system sensitivities and S cone acuity were obtained from three patients with ESCS. The results were qualitatively consistent with the presence of more S cones and more S cone ganglion cells. To test this hypothesis further, a model of the receptoral and post-receptoral components of the S cone system was used in conjunction with psychophysical measurements of S cone system sensitivity under flashed and steady-state adaptation conditions. Within the context of the model, the data were consistent with an increase in the number of S cones and S - (L + M) ganglion cells and with a decrease in the total L + M cone input to each S - (L + M) ganglion cell

PURPOSE: To assess changes in measures of visual function in patients with retinitis pigmentosa (RP) over time. METHODS: Patients with RP and visual acuity of 20/40 or better and central visual fields of 10 degrees or larger were enrolled in a 9-year prospective study. The following measures of visual function were obtained annually over the follow-up period: visual acuity, Goldmann visual fields (V4e target), focal electroretinograms, and hue discrimination. RESULTS: Over the follow-up period, the averaged group data showed changes in all measures of visual function. The smallest amount of change occurred for visual acuity and hue discrimination, and the greatest amount of change occurred for visual field area. Examination of individual patient data over the follow-up period indicated that the rates of change varied among patients and that losses in function for one measure did not correlate well with losses on other measures. CONCLUSIONS: These results stress that although visual function deteriorated over time for this group of patients with RP, there were differences among our measures of visual function. Measures that primarily assess central retinal function change relatively slowly compared with measures that assess more peripheral retinal function