Recording multifocal electroretinograms with fundus monitoring

To record multifocal electroretinograms (ERGs) with simultaneous fundus monitoring.

An infrared television fundus camera was used to monitor the fundus. A tightly packed array of 19 yellow light-emitting diodes (LEDs) was used as the stimulus source and LEDs were alternated between on and off according to a binary m-sequence at a rate of 75 Hz. The stimulus array subtended approximately 25 degrees of the visual angle. Multifocal ERGs were recorded with a Burian-Allen bipolar contact lens electrode from two normal subjects and a patient with macular dystrophy.

When the center of the stimulus was positioned on the fovea, the amplitude of the response was largest at the fovea and decreased toward the peripheral retina; the response pattern corresponded to the spatial distribution of cone cells. When the center of the stimulus was positioned on the optic disc, the response at the optic disc was undetectable. A reliable multifocal ERG was obtained from a patient with macular dystrophy.

This system made it possible to monitor the stimulus on the fundus and to adjust the stimulus to the correct retinal locations with exact focusing. The authors' findings indicate that this method especially can be useful in patients with poor fixation. In addition, the authors' results suggests that the stray light effect in the multifocal stimulus system is minimal if any.