Contributor: Gordon K. Klintworth
Retinitis pigmentosa (pigmentary retinopathy) is a clinically and genetically heterogeneous group of retinal degenerations that primarily affect the rod photoreceptors. Initial symptoms include nyctalopia during adolescence. A ring scotoma develops and extends peripherally until only a small visual field remains (tunnel vision, visual field constriction), which too is eventually lost. Fundoscopic exam reveals extremely attenuated retinal blood vessels. Eventually the electroretinogram shows no activity. The optic disc develops a waxy yellowish pallor due to glial proliferation. The retinal pigment epithelium atrophies and becomes mottled gray with hyperpigmented and hypopigmented areas. The intraretinal pigment has been likened to bone spicules or the appearance of bone corpuscles. The choriocapillaris eventually atrophies, exposing large vessels and a whitish yellow choroid. Retinitis pigmentosa has many causes and numerous types are recognized. Based on the mode of inheritance retinitis pigmentosa can be divided into autosomal dominant [retinitis pigmentosa - autosomal dominant], autosomal recessive [retinitis pigmentosa - autosomal recessive] and X-linked [retinitis pigmentosa - X-linked] and Y-linked [retinitis pigmentosa - Y-linked] types. Retinitis pigmentosa is a manifestation of numerous syndromes. At least 39 genes and loci have identified in non-syndrome retinitis pigmentosa. Mutations in numerous different genes, including ABCR, CERKL, CRB1, IMPDH1, MTTS2, NRL, ORP1, PDE6A, PDE6B, RDS, RHO, RLBP1, RPE65, PRKCG, TULP1 cause retinitis pigmentosa. Some of them code for members of the rod phototransduction cascade.One form of autosomal recesive retinitis pigmentosa maps to the region of the gamma-aminobutyric acid-receptor gene (including autosomal recessive retinitis pigmentosa). Several ocular disorders have been reported in association with retinitis pigmentosa, but in most cases the significance of the association remains unknown. It many incidences it may be coincidental. Associations include keratoconus, myopia, posterior subcapsular cataract [cataract - posterior subcapsular], cystoid macular degeneration [macular degeneration - cystoid], and optic disk drusen [drusen - optic nerve] or hamartomas. Cataract (especially posterior subcapsular cataract) [cataract - posterior subcapsular] is the most frequent anterior segment abnormality in retinitis pigmentosa.