Other Retinal Conditions
Refsum disease is an extremely rare and complex disorder that affects many parts of the body. A form of the retinal degenerative disease known as retinitis pigmentosa (RP) is a common feature of this disease.
Rod-cone dystrophy results from a primary loss of rod photoreceptors, followed by loss of cones.
The characteristics are congenital, static hemeralopia and diffuse yellow or gray coloration of the fundus. After 2 or 3 hours in total darkness, the normal color of the fundus returns. The condition is more frequent in Japanese. See hemeralopia (310500) for a comment on the use of this term, as opposed to the term nyctalopia.
Characteristically small round white spots (drusen) involving the posterior pole of the eye, including the areas of the macula and optic disc, appear in early adult life. Progression to form a mosaic pattern which Doyne (1899) aptly termed 'honeycomb' occurs thereafter. Doyne considered it to represent 'choroiditis.' However, Collins (1913) showed that the changes consisted of swelling in the inner part of Bruch membrane. Failing vision usually developed considerably later than the ophthalmologic change. Robert Walter Doyne (1857-1916) was an ophthalmologist in Oxford, England. Pearce (1967) did an extensive study of 6 kindreds living near Oxford. Some and possibly all may have been descendants from a common ancestor. Dominant inheritance with complete manifestation of the trait in persons surviving beyond early adult life was found. Families living elsewhere than England have been reported (see references given by Pearce, 1968). Maumenee (1982) suggested that this may be fundamentally the same disorder as drusen of Bruch membrane (126700).
Cone-rod retinal dystrophy (CRD) characteristically leads to early impairment of vision. An initial loss of color vision and of visual acuity is followed by nyctalopia (night blindness) and loss of peripheral visual fields. In extreme cases, these progressive symptoms are accompanied by widespread, advancing retinal pigmentation and chorioretinal atrophy of the central and peripheral retina (Moore, 1992). Evans et al. (1995) found complete blindness (no light perception) in only 3 of the 34 patients studied, and these 3 were all over 65 years of age. Serious effects on visual acuity (light perception only) were present in 10 other patients; however, their mean age was 60.3 years. All other patients retained some visual acuity. In many families, perhaps a majority, atrophy of the central and peripheral choreoretinal atrophy is not found (Tzekov, 1998).
Blue cone monochromatism is characterized by poor central vision and color discrimination, infantile nystagmus, and nearly normal retinal appearance. The psychophysiologic functions of both rods and blue cones are preserved (Lewis et al., 1987). The frequency of achromatopsia is said to be approximately 1 in 100,000 persons. The first detailed description is that given by Huddart (1777). The subject of that report 'could never do more than guess the name of any color; yet he could distinguish white from black, or black from any light or bright color...He had 2 brothers in the same circumstances as to sight; and 2 brothers and sisters who, as well as his parents, had nothing of this defect.' This disorder was previously interpreted as total colorblindness. Information presented by Spivey (1965) indicated that affected persons can see small blue objects on a large yellow field and vice versa. These cases have been variously called partial complete colorblindness, or incomplete achromatopsia. Blackwell and Blackwell (1961) have described achromatopic families in which a few blue cones seemed to be present. See comments of Alpern et al. (1960). Sloan (1964) also had evidence of the presence of a few red cones in cases of otherwise complete achromatopsia. Bromley (1974) showed me a large kindred with this disorder in a typical X-linked recessive pattern.