Recovery of photoreceptor outer segment length and analysis of membrane assembly rates in regenerating primate photoreceptor outer segments.

PURPOSE Photoreceptor outer segments are in a dynamic state of membrane addition and disposal. This study was undertaken to determine how a standardized period of retinal detachment and varying periods of reattachment affect the renewal process. METHODS To investigate the effects that retinal detachment and reattachment may have on this process, the neural retina from 12 adult rhesus monkeys (Macaca mulatta) was detached from the overlying retinal pigment epithelium (RPE) by subretinal injection of a balanced salt solution. After a standardized detachment period of 7 days, the two tissue layers were reapposed. Animals were labeled with 3H-fucose and killed at times ranging from 3-150 days after reattachment. RESULTS During the 7 day detachment period, the majority of rod outer segments (ROS) and cone outer segments (COS) degenerated, but inner segments remained intact. During the first week after reattachment, a rapid increase in rod and cone outer segment length occurred in the absence of disc shedding. This was accompanied by re-establishment of a modified morphologic relationship between the apical processes of the RPE and the regenerating outer segments. ROS and COS regained approximately 40% of their control lengths after a 2 wk reattachment period. By 30 days of reattachment, ROS had regained 72% of their normal length and COS had regained approximately 48%. After 150 days of reattachment, photoreceptor outer segment mean length was not statistically different from control areas. Autoradiographic results confirmed that new disc membranes were synthesized after reattachment. The rate of ROS membrane assembly was subnormal at reattachment time points up to 30 days. CONCLUSIONS Retinal detachment leads to a reduction in photoreceptor outer segment absolute length and membrane assembly rates. Increasing time of retinal reattachment is positively correlated with an increase in outer segment absolute length and a corresponding increase in membrane assembly rates. This recovery pattern in eyes without underlying pathology and after a relatively brief detachment interval may represent the upper limit of the recovery process.