Nomarski evaluation of rod outer segment renewal in a hereditary retinal degeneration. Comparison with autoradiographic evaluation.

Differential interference contrast (Nomarski) optics and autoradiography were used to estimate independently the rate of outer segment renewal in the early stages of progressive rod-cone degeneration (PRCD) in dogs. We have found that significant reductions in renewal rate are demonstrable using the two methods of analysis: autoradiography = 34% reduction; Nomarski method = 18% reduction. Nomarski analysis of affected rod outer segments (ROS) demonstrated optical periodicities (light/dark bands) extending from the base to the tip of the outer segment. Nineteen percent of the cells, however, showed areas where the light/dark bands were not apparent. These homogeneous, "optically silent" regions were interpreted to possibly represent areas where the disc orientation was not perpendicular to the long axis of the ROS.