The first symptom is usually an impairment of twilight vision (nyctalopia). Under dim light, the visual fields tend to constrict; but slowly, as the disease progresses, there is permanent visual impairment in all degrees of illumination. The perimacular zones tend to be the first and most severely involved, giving rise to partial or complete ring scotomata. Peripheral loss sets in later. Usually both eyes are affected simultaneously, but cases are on record where 1 eye was affected first and more severely. Ophthalmoscopic examination shows the characteristic triad of pigmentary deposits that assume the configuration of bone corpuscles, attenuated vessels, and pallor of the optic discs. The pigment is caused by clumping of epithelial cells that migrate from the pigment layer to the superficial parts of the retina as the rod cells degenerate. The pigmentary change spares only the fovea, so that eventually the world is perceived by the patient as though he were looking through narrow tubes.
The many and diverse syndromes to which retinitis pigmentosa may be linked include oligophrenia, obesity, syndactyly, and hypogonadism (Bardet-Biedl syndrome); hypogenitalism, obesity, and mental deficiency (Laurence-Moon syndrome); Friedreich and other types of spinocerebellar and cerebellar ataxia; spastic paraplegia and quadriplegia with Laurence-Moon syndrome; neurogenic amyotrophy, myopia, and color-blindness; polyneuropathy and deafness (Refsum disease); deaf mutism; Cockayne syndrome and Bassen-Kornzweig disease; and several mitochondrial diseases, particularly progressive external ophthalmoplegia and Kearns-Sayre syndromes.
This is a bilaterally symmetrical, slowly progressive macular degeneration, differentiated from retinitis pigmentosa by Stargardt in 1909. In essence, it is a hereditary (usually autosomal recessive) tapetoretinal degeneration or dystrophy (the latter term being preferred by Waardenburg), with onset between 6 and 20 years of age, rarely later, and leading to a loss of central vision. The macular region becomes gray or yellow-brown with pigmentary spots, and the visual fields show central scotomata. Later the periphery of the retina may become dystrophic. The lesion is well visualized by fluorescein angiography, which discloses a virtually pathognomonic “dark choroid” pattern. Activity in the electroretinogram is diminished or abolished. Both recessively inherited Stargardt disease and the closely related cone-rod dystrophy have been linked to mutations of ABCA4 or ELOVL4 the former codes for a transporter protein (termed ABCR) of the photoreceptor.
This disease, with its selective loss of cone function, is in a sense the inverse of retinitis pigmentosa. According to Cohan and associates, it may be associated with epilepsy, Refsum syndrome, Kearns-Sayre syndrome, Bassen-
Kornzweig syndrome, or Sjögren-Larsson syndrome, or with spinocerebellar and other forms of cerebellar degeneration and familial paraplegia.
SYNDROME OF CONGENITAL OR PROGRESSIVE DEAFNESS (SEE CHAP. 14)