Laser Focal Electroretinography Reveals Unique Macular Responses

We have constructed an instrument that allows us to view the fundus and a laser beam that can be shifted to different positions on the retina. The helium-neon laser subtends approximately 3° of visual angle and is square wave flickered with equal light/dark cycles at 5.1 Hertz. We can shift from a 633 nm to a 544 nm laser allowing a comparison of responses to two different parts of the spectrum. The electroretinogram (ERG) produced by the flicker is detected by an electrode embedded in a corneal contact lens. Retinal adaptation is maintained by a steady white light, bright enough to permit easy viewing of the fundus and to minimize responses to scattered light and sufficient to completely saturate rod responses. The studies reported here have been carried out on four eyes of two normal rhesus monkeys tested under anesthesia repeatedly over a period of one year.