Retinal Architecture in ​RGS9- and ​R9AP-Associated Retinal Dysfunction (Bradyopsia)

Purpose: To characterize photoreceptor structure and mosaic integrity in subjects with ​RGS9- and R9AP-associated retinal dysfunction (bradyopsia) and compare to previous observations in other cone dysfunction disorders such as oligocone trichromacy.

Design: Observational case series.

Methods: setting: Moorfields Eye Hospital (United Kingdom) and Medical College Wisconsin (USA).

Study population: Six eyes of 3 subjects with disease-causing variants in ​RGS9 or R9AP.

Main outcome measures: Detailed retinal imaging using spectral-domain optical coherence tomography and confocal adaptive-optics scanning light ophthalmoscopy.

Results: Cone density at 100 μm from foveal center ranged from 123 132 cones/mm(2) to 140 013 cones/mm(2). Cone density ranged from 30 573 to 34 876 cones/mm(2) by 600 μm from center and from 15 987 to 16,253 cones/mm(2) by 1400 μm from center, in keeping with data from normal subjects. Adaptive-optics imaging identified a small, focal hyporeflective lesion at the foveal center in both eyes of the subject with RGS9-associated disease, corresponding to a discrete outer retinal defect also observed on spectral-domain optical coherence tomography; however, the photoreceptor mosaic remained intact at all other observed eccentricities.

Conclusions: Bradyopsia and oligocone trichromacy share common clinical symptoms and cannot be discerned on standard clinical findings alone. Adaptive-optics imaging previously demonstrated a sparse mosaic of normal wave-guiding cones remaining at the fovea, with no visible structure outside the central fovea in oligocone trichromacy. In contrast, the subjects presented in this study with molecularly confirmed bradyopsia had a relatively intact and structurally normal photoreceptor mosaic, allowing the distinction between these disorders based on the cellular phenotype and suggesting different pathomechanisms.