Extracellular analysis of the electrical activity of photoreceptors in the retinae of rats and mice with inherited retinal degenerations will be studied. Patterns of light induced current associated with abnormal receptor activity will be compared to control preparations in an attempt to localized and define the early stages or receptor abiotrophy. A pair of micropipettes are inserted into a piece of isolated retina, mounted so that the normal anatomical relationships are preserved. The radial spacing of the pipettes are under experimental control and the resistance of the tissue between them is measured by passing current pulses. Radial photocurrent can thus be calculated for several depths along the receptor axis. Moreover, the waveforms of the voltage changes are specific to a particular region along the receptor. Electrical analysis of receptors undergoing degenerative changes provide a precise functional definition of the nature and location of the lesion which may also have relevance to analogous retinal diseases in man.