Evaluation of outer nuclear layer overshadowed by retinal vessels in retinitis pigmentosa

We investigated in vivo light-induced photoreceptor damage in retinitis pigmentosa (RP) using spectral-domain optical coherence tomography (SD-OCT) images.

We retrospectively reviewed patients with genetic diagnosis of EYS-associated RP. The outer nuclear layer (ONL) thickness under retinal vessels was measured on SD-OCT vertical scans. As a control, we measured adjacent ONL thickness 100 μm superior and inferior from the vessel. Same measurements were performed in healthy subjects. We calculated the ratio of ONL thickness under vessel divided by the average of adjacent ONL thickness and defined as ONL preservation ratio. In patients with RP, the length of ellipsoid zone (EZ) from the fovea was also measured with SD-OCT vertical scans.

Thirty EYS-associated RP patients and 25 healthy subjects were included. In both groups, ONL thickness overshadowed by retinal vessels was not significantly different from that of adjacent area. However, ONL preservation ratio of RP was larger than that of healthy control in both superior and inferior retina (1.03 vs 0.97; p < 0.01, 1.15 vs 0.95; p < 0.01, respectively). In RP, ONL preservation ratio was significantly larger in the inferior retina than superior retina (p < 0.01). Furthermore, in RP patients, the EZ length from the fovea was always shorter in the inferior than superior retina and there was a significant difference (p < 0.01).

Patients with EYS-associated RP exhibited inferior-dominant photoreceptor death and the relative ONL preservation under retinal vessels. These results suggest that longitudinal environment light exposure may be correlated with the photoreceptor death.