Photoreceptor decay over time and apoptosis in experimental retinal detachment.

BACKGROUND: Data are scarce on the actual rate and mode of outer nuclear layer decay in retinal detachment (RD). We used an experimental rabbit model to assess the presence of apoptosis and rate of photoreceptor death following RD. This model included the creation of localized and stable retinal blebs, while controlling for any decline of retinal elevation over time.
METHODS: RD was produced in New Zealand white rabbits by injecting 0.05 ml of 15% sodium hyaluronate (Healon GV) under the neural retina using a microsurgical technique. Animals were killed at 1, 2, 4, 7, 14 and 29 days. Retinal tissue was processed for light and electron microscopy and for in situ end labeling of fragmented DNA using a modification of the TUNEL technique. Photoreceptor cell nuclei were counted in the RD areas of maximum retinal elevation of 28 eyes, and an additional 4 eyes were used for nick end labeling.
RESULTS: Positive DNA nick end labeling, ultrastructural features and absence of necrotic cells indicated apoptotic photoreceptor cell death. Also, there was a rapid, almost linear elimination of photoreceptor nuclei over time. At 14 days only half of the number of nuclei were discernible, while approximately one tenth remained after 29 days. There was a statistically significant, but minimal decline in RD height over the 4 weeks of study.
CONCLUSION: Following experimental RD in rabbits, apoptotic cell death is associated with an almost linear elimination of photoreceptor cells over time. The use of highly viscous sodium hyaluronate in separating the neural retina from the retinal pigment epithelium allows the RD to maintain a nearly constant height over a period of 4 weeks.