Assessing Photoreceptor Reflectance And Structure In Congenital Stationary Night Blindness

Abstract

Purpose: : The clinical manifestations of the stationary night blindness disorders with a normal fundus are predominantly due to defects in retinal neurotransmission, but little is known about the structure and functional characteristics of the photoreceptors in these conditions. Here we used high-resolution retinal imaging to examine photoreceptor morphology and changes in photoreceptor reflectance post-dark adaptation in patients with complete congenital stationary night blindness (CSNB) and Oguchi disease.

Methods: : We recruited three patients with CSNB due to mutations in GRM6 (JC_0550: p.Gly58Arg; JC_0682: p.Gly756Asp; JC_0684: p.Arg677Cys), one patient with Oguchi disease (DH_0491: unknown mutation), and one normal control (JC_0677). SD-OCT images were taken of the macula, and retinal thickness was measured. An adaptive optics scanning light ophthalmoscope (AOSLO) was used to examine the integrity of the rod and cone mosaic, with photoreceptor density calculated at various retinal eccentricities. We imaged four of the five subjects following a 2-hour dark adaptation to examine photoreceptor reflectance changes over a ~45 minute recording period, both at the fovea and in a single peripheral location.

Results: : On SD-OCT all major retinal layers were visible with no evidence of disruption; however, retinal thickness was reduced in the parafoveal region in the three patients with GRM6 mutations. A sub-layer analysis revealed that this thinning was due to decreased thickness of the inner retinal layers, with normal outer retinal layers. All patients had normal rod and cone density at all locations imaged. Upon removal from dark adaptation, the rods in the patient with Oguchi disease gradually and significantly increased reflectance. This was not observed in the two GRM6 patients or the normal control.

Conclusions: : Our data suggest entirely normal rod and cone structure in the three CSNB patients with GRM6 mutations, however there was significant thinning of the inner retinal layers in these patients. Oguchi disease is characterized by a golden tapetal-like reflex under light-adapted conditions, which reverses after dark adaptation. Our finding that rods, but not cones, change reflectivity after dark adaptation suggests that this change in reflectance is due to changes within the rod photoreceptor as opposed to global changes in a different outer retinal layer.

Keywords: photoreceptors • retina: distal (photoreceptors, horizontal cells, bipolar cells) • imaging/image analysis: non-clinical