PURPOSE. To evaluate the characteristics of stray light-induced response in multifocal ERG (mfERG) elicited by the stimulus falling on the disc. METHODS. A patient with an enlarged optic disc (4 X 4 disc diameters of disc of normal fellow eye) and four normal volunteers served as subjects. The mfERGs elicited by different stimulus intensities (0.67-4.67 cd-sec/m2) were recorded from the patient, and the mfERGs obtained with stimuli on the enlarged optic disc. For comparison, full-field pseudorandom ERGs (ffprERGs) were also recorded in all subjects. The first-order kernels (K1) and the second-order kernels (K2.1) were analyzed. RESULTS. A small and delayed K1 was recorded on the enlarged disc, but K2.1 was flat on the disc at all intensities. The implicit time of K1 at lower intensities was longer than at higher intensities. ffprERGs at very low intensities in the patient and normal subjects were similar to the mfERG on the disc (delayed K1 associated with flat K2.1). CONCLUSIONS. The responses elicited by stimulating the disc were delayed in K1 and flat in K2.1. Because similar ffprERGs were observed at very low intensities, it is likely that an optic disc with high reflectance scattered the stimulus light to create a weak full-field stimulus. Thus, care must be taken when focal lesions are investigated with mfERGs.
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