Metrics details. CRDs are characterized by retinal pigment deposits visible on fundus examination, predominantly localized to the macular region. In contrast to typical retinitis pigmentosa RP , also called the rod cone dystrophies RCDs resulting from the primary loss in rod photoreceptors and later followed by the secondary loss in cone photoreceptors, CRDs reflect the opposite sequence of events. CRD is characterized by primary cone involvement, or, sometimes, by concomitant loss of both cones and rods that explains the predominant symptoms of CRDs: decreased visual acuity, color vision defects, photoaversion and decreased sensitivity in the central visual field, later followed by progressive loss in peripheral vision and night blindness.
The clinical course of CRDs is generally more severe and rapid than that of RCDs, leading to earlier legal blindness and disability. Non syndromic CRDs are genetically heterogeneous ten cloned genes and three loci have been identified so far. It is likely that highly deleterious mutations in genes that otherwise cause RP or macular dystrophy may also lead to CRDs.
The diagnosis of CRDs is based on clinical history, fundus examination and electroretinogram. Molecular diagnosis can be made for some genes, genetic counseling is always advised.
Currently, there is no therapy that stops the evolution of the disease or restores the vision, and the visual prognosis is poor.
Management aims at slowing down the degenerative process, treating the complications and helping patients to cope with the social and psychological impact of blindness. CRDs present first as a macular disease or as a diffuse retinopathy with predominance of the macular involvement. In contrast to the symptoms of the rod cone dystrophies RCDs, typical retinitis pigmentosa resulting from predominant rod involvement, i.
