Abstract
Purpose :
It is well known that one of the earliest signs of retinitis pigmentosa (RP) progression is the shortening of photoreceptor outer segments (OSs). However other structural changes inside the OS may accompany or even precede this shortening. Using adaptive optics optical coherence tomography (AO-OCT) along with the cone optoretinogram, we sought to determine whether structural changes—manifested as reflectance variations along OS—could be detected in the cone OSs of patients with RP.
Methods :
Two subjects with RP and two age-matched controls were imaged using AO-OCT at 2°, 4°, and 6° temporal (T) retina with 1°×0.8° field of view. The cone optoretinogram was measured at each location with three stimulus wavelengths (637nm, 528nm, and 450nm). All reflection peaks posterior to the inner/outer/segment junction (IS/OS) were identified and their functional responses were measured. The true COST was identified as the most posterior reflection with a clear cone-like response. Cones with extra OS reflections brighter than their COST were recorded.
Results :
In both RP subjects, significantly shorter cone OSs were observed within the transition zone (TZ), which separates healthy from severely diseased retina. Within the TZ, 42.5%, 39.7%, and 71.9% of cones at 6°T of RP1, and 4°T and 6°T of RP2, respectively, exhibited OS lengths that were shorter than the 99.7% confidence interval (CI) of the controls. By contrast, less than 5% of cones exhibited OS shortening within the relatively healthy central island (RP1: 2°T, 4°T and RP2: 2°T). Despite the correlation between OS length and tissue health, cones in RP subjects with normal OS lengths were more likely to have extra OS reflections brighter than COST than those in controls. This likelihood increased with the severity of the disease. In healthy controls, the percentage of normal-length cones (99.7% CI) with such OS reflections was small and varied little between locations (4.4 ± 2.2%). For normal-length cones in RP1 (RP2), these percentages were 9.3% (4.2%), 12.1% (18.0%), and 28.9% (30.0%) at 2°T, 4°T, and 6°T, respectively.
Conclusions :
In the TZ, many cones showed drastic OS shortening. The remaining cones with normal OS lengths were up to 7X more likely to exhibit extra bright reflections in their OSs compared to controls. This suggests that cones with normal OS lengths may already be compromised by the disease.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.