Título

CONE DYSTROPHY WITH SUPERNORMAL ROD RESPONSES

Objetivo

Objective: To report a case of Cone Dystrophy with Supernormal Rod Responses (CDSRR)

Relato do Caso

A 9-year-old male of Caucasian ethnicity presented with low visual acuity. Best corrected visual acuity (BCVA) was 20/80 in both eyes [Oculus Uterque (OU)]. Family history showed parental consanguinity. Biomicroscopy of the anterior segment was unremarkable. Eye fundus showed mottled macules in OU. The Farnsworth D-15 panel color vision test revealed a tritanopia pattern. Spectral-Domain Optical Coherence Tomography (SD-OCT) showed disrupted foveal ellipsoid bands (Arrows, Figure 1). The International Society of Electrophysiology and Vision protocol was followed in electrophysiological assessment. Full-field electroretinogram (FF-ERG) of the right eye indicated reduced b-wave amplitude to dark-adapted 0.01 cd•s•m-2 (DA 0.01) stimulus, whereas a-wave and b-wave amplitudes were supernormal to moderate and bright flash (DA 3.0 cd•s•m-2 and DA 10.0 cd•s•m-2). Light-adapted responses showed reduced amplitudes. Other than the dim scotopic flash, all peak times were normal or delayed (Figure 2).

Conclusão

The presented case is compatible with Cone Dystrophy with Supernormal Rod Responses (CDSRR). The condition has a genetic base with an autosomal recessive inheritance pattern. The visual acuity decreases at a young age and it can also be reported with nyctalopia, dyschromatopsia, and photophobia. The FF-ERG exhibits a pathognomonic pattern. In dark-adapted conditions, the b-wave shows diminished amplitudes to a dim flash but supernormal amplitudes after moderate to high-intensity stimulus. It appears that KCNV2 voltage-gated potassium channels play a role in the pathogenesis of CDSRR. Therefore, this case is a rare report and has importance to the Ophthalmology field due to its singularity, research, and educational potential.