Variation of temporal stimulus characteristics to evaluate visual function prior to pars plana vitrectomy.

Electrophysiological examinations were carried out prior to pars plana vitrectomy in a series of consecutive patients with complicated diabetic retinopathy, proliferative vitreoretinopathy, and perforating injuries. In 141 eyes electroretinograms were evaluated. The amplitude of the a- and b-waves at dark and light adaptation and of the 30-Hz flicker response correlated with the postoperative visual acuity and the retinal morphology. Due to the variability of these parameters, however, the preoperative electroretinogram has no predictive value. In 245 eyes, flash and flicker (5, 10, 20, 30 Hz) visual evoked cortical potentials (VECP) were recorded. The flash VECP was of no value. The presence of a response to a flicker stimulus of 10 Hz or higher frequencies, however, indicated a better functional recovery (P < 0.02). More eyes with an attached central retina showed a 30-Hz flicker response as compared to eyes with central retinal detachment (P < 0.01). The flicker VECP therefore, has a predictive value prior to vitrectomy.