Preservation of the inner retina in retinitis pigmentosa - A morphometric analysis

Objective: To determine the extent of preservation in the inner retina in retinitis pigmentosa (RP). Methods: We analyzed sectioned maculae of 21 post-mortem eyes with RP and 19 age-matched, normal, post-mortem eyes. Eyes were divided into 2 groups: severe and moderate RP. Cell nuclei were counted in the outer nuclear, inner nuclear, and ganglion cell layers within thirty 100-mu m intervals from the foveola to 1500-mu m eccentricity. Results: Statistically significant (P less than or equal to.05) loss of both the outer nuclear and ganglion cell layers was present in the groups with moderate and severe RP when compared with the control groups. However, even in the group with severe RP, 30% of the ganglion cells were histologically intact. Similarly, 78% and 88% of the inner nuclear layer cells were preserved in the groups with severe and moderate RP, respectively. Different inheritance modes showed no statistically significant differences in any of the retinal layers. Conclusions: Despite a statistically significant (P less than or equal to.05) loss of cells found in all retinal layers, a large percentage of the inner retinal neurons remained histologically intact. Current experimental therapies, such as photoreceptor transplantation and implantation of a visual prosthesis, are based on the premise that some inner retinal neurons are preserved after death of photoreceptors in RP. Our observations support this assumption.