ISOLATION OF FOCAL ROD ELECTRORETINOGRAMS FROM THE DARK-ADAPTED HUMANEYE

Purpose, To isolate focal rod electroretinograms (ERGs) from the dark- adapted human eye. Methods, In two normal volunteers, dark-adapted foc al rod ERGs were recorded from the peripheral retina in response to 30 degrees diameter blue flashes of varying retinal illuminance and from different retinal regions in response to 10 degrees diameter bright b lue flashes. Dark-adapted focal rod ERGs also were recorded from a pat ient with the multiple evanescent white dot syndrome (MEWDS) and an en larged blind spot in response to 30 degrees diameter blue flashes pres ented within and outside the scotoma. The slower and larger stray ligh t rod component elicited by these flashes was removed by subtracting t he matching rod response to a dimmer, full-field flash, or was ignored when it did not overlap the faster and smaller focal rod component. R esults. The focal rod ERG had a waveform and sensitivity similar to th ose of the full-field rod ERG, was approximately proportional in ampli tude to the density of rods directly illuminated, and was nondetectabl e within the retinal area corresponding to the enlarged blind spot of the patient with MEWDS. Conclusions, Focal rod ERG a- and b-waves, in response to stimuli as small as 10 degrees, can be recorded from diffe rent regions of the dark-adapted human retina to evaluate localized ro d function.