EVIDENCE FOR PHOTORECEPTOR CHANGES IN PATIENTS WITH DIABETIC-RETINOPATHY

Purpose. To determine whether the rod and cone photoreceptors are affe cted in patients with diabetic retinopathy. Methods. Twelve patients w ith diabetes and varying levels of retinopathy and nine age-similar co ntrol observers participated in this study. Two-color (500 versus 650 nm) dark-adapted thresholds were measured as a function of retinal ecc entricity. Full-field flash electroretinograms were obtained using bri ef, high-intensity flashes. Dark-adapted rod-isolated (Wratten 47B fil ter) and light-adapted cone-isolated (Wratten 26 filter) electroretino graphic responses were measured as a function of flash intensity. The a-wave data were fitted with a model based on photopigment transductio n to obtain values for the parameters of R-max (the maximal response) and log S (sensitivity). Standard clinical 30-Hz nicker electroretinog raphic responses were also measured. Results. Psychophysically measure d dark-adapted thresholds were elevated primarily at eccentricities of 5 degrees and 10 degrees from the fovea. Analysis of rod and cone a-w ave data showed that R-max was normal in most of the patients, but log S was reduced. Analysis of b-wave and oscillatory potential parameter s 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 electrophysi ological results were not significantly correlated with blood glucose or glycosylated hemoglobin level. Conclusions. The results provide evi dence for rod and cone receptoral and postreceptoral deficits in patie nts with diabetic retinopathy. The photoreceptor changes are primarily in the log S (sensitivity) parameter and are attributed to transducti on abnormalities.