Rod-driven focal macular electroretinogram

PURPOSE: To determine the stimulus conditions required to elicit rod-driven, focal macular electroretinograms (rod FMERGs). METHODS: A blue (lambda(max)=470 nm) stimulus, 5 degrees in size, was imaged at a luminance of 1.5 cd/m(2) on different regions of the human retina. Electroretinograms (ERGs) elicited by this stimulus were recorded from the light- and dark-adapted retina of four subjects without any ophthalmological abnormalities. A subject with cone dystrophy was also tested by this method. RESULTS: Stimulus luminance <==1.5 cd/m(2) did not elicit a response when it was imaged on the optic disc, but higher intensities elicited a small b-wave from stray light. When this stimulus was imaged on the macular area or the 15 degrees temporal retina, an ERG was elicited that had the shape of the full-field scotopic ERG. This stimulus with a luminance of 1.5 cd/m(2) did not elicit a response from stimulation of the macular area of a light-adapted retina but elicited a slow-rising positive b-wave after 30 minutes of dark adaptation. In a subject with cone dystrophy, focal rod response was elicited from the macula, despite no response under photopic conditions. CONCLUSION: We conclude that this stimulus will elicit a response that is derived exclusively from rods and is a focal response with no contribution from stray light.