On–/Off – Ganzfeld ERG With LED Stimulation in Normal Subjects

Abstract

Abstract: : Purpose: Recent work indicates the diagnostic values of the photopic negative response (PhNR) and the long duration stimulus. Aim was to record the on– and off– responses of the photopic ganzfeld electroretinogram (ERG) using a LED stimulator and to explore how each ERG component (a–, b– wave, PhNR in on–set, d–wave, PhNR in off–set) changes in different stimulus condition. Methods: Photopic Ganzfeld ERGs were recorded in response to a white bright LED flash on a white background. Background illumination was changed in 5cd/m² steps from 15cd/m² to 30cd/m². Flash intensities were 40, 60, 80, 100 and 120cd/m². Using constant flash duration (250ms) the off– period was 250, 350, 500 and 750ms. The ERGs were recorded with a JET contact lens electrode. Complete series were studied in two normal subjects. Nine normal subject and 5 glaucoma patients have been studied with all flashes and off periods at a background illumination of 20 cd/m². Results: PhNR was not significantly influenced by the variation of background intensity or inter stimulus interval as used in this study. At a fixed background illumination the PhNR–on, the b–wave, the d–wave increased with increasing flash intensities while PhNR–off stayed constant. Comparison to the results of normals and glaucomas, differences were most expressed in PhNR of the offset component. Conclusions: On and off response of the human ERG depend on increasing flash intensity. The off period and background illumination seems to have no significant influence in the amplitude of the off– and on–PhNR. Glaucoma patients show a reduction of the amplitude of the PhNR following the d–wave. These results indicate that separate analysis of on–and off– PhNR might be helpful in glaucoma examination.

Keywords: electrophysiology: clinical • clinical research methodology