Phenotypic Characteristics Including In Vivo Cone Photoreceptor Mosaic inKCNV2-Related “Cone Dystrophy with Supernormal Rod Electroretinogram”

Abstract

To report phenotypic characteristics including macular cone photoreceptor morphology in KCNV2-related "cone dystrophy with supernormal rod electroretinogram" (CDSR). Seven patients, aged 9 to 18 years at last visit, with characteristic full-field electroretinographic (ERG) features of CDSR were screened for mutations in the KCNV2 gene. All patients underwent detailed ophthalmological evaluation, which included distance and color vision testing, contrast sensitivity measurement, fundus photography, fundus autofluorescence (FAF) imaging, and spectral domain-optical coherence tomography (SD-OCT). Follow-up visits were available in six cases. Rod photoreceptor function was assessed using a bright white flash ERG protocol (240 cd·s/m(2)). Macular cone photoreceptor morphology was assessed from 2° by 2° zonal images obtained using adaptive optics scanning laser ophthalmoscopy (AOSLO) in six cases. Pathogenic mutations in KCNV2 were identified in all seven cases. Best corrected vision was 20/125 or worse in all cases at the latest visit (20/125-20/400). Vision loss was progressive in two cases. Color vision and contrast sensitivity was abnormal in all cases. Retinal exam revealed minimal pigment epithelial changes at the fovea in four cases. A peri- or parafoveal ring of hyperfluorescence was the most common FAF abnormality noted (five cases). The SD-OCT showed outer retinal abnormalities in all cases. The rod photoreceptor maximal response was reduced but rod sensitivity was normal. AOSLO showed markedly reduced cone density in all six patients tested. Central vision parameters progressively worsen in CDSR. Structural retinal and lipofuscin accumulation abnormalities are commonly present. Macular cone photoreceptor mosaic is markedly disrupted early in the disease.