Cone dystrophy with supernormal rod response – A rare case report

Abstract

Cone dystrophy with supernormal rod response (CDSRR), also known as potassium channel subfamily V, member 2 (KCNV2) retinopathy, is a rare autosomal recessive cone rod dystrophy, which derives its name from its characteristic full-field electroretinography (ERG) features and the causative gene mutation (KCNV2 gene). It is one of the rare eye retinal dystrophies where ERG is pathognomonic and directly carries the genetic imprint of the condition. Here, we discuss the case of a 9-year-old Indian child with history of diminution of vision in both eyes. Full-field ERG showed a characteristic response of supranormal scotopic b-wave amplitude at high luminance intensities along with broadened trough of the a-wave with late negative component with reduced and delayed photopic response suggestive of CDSRR.