Blue cone (OPN1SW; 613522) monochromatism is a rare X-linked congenital stationary cone dysfunction syndrome characterized by the absence of functional long wavelength-sensitive and medium wavelength-sensitive cones in the retina. Color discrimination is severely impaired from birth, and vision is derived from the remaining preserved blue (S) cones and rod photoreceptors. BCM typically presents with reduced visual acuity, pendular nystagmus, and photophobia. Patients often have myopia (review by Gardner et al., 2009). There is evidence for progression of disease in some BCM families (Nathans et al., 1989; Ayyagari et al., 2000; Michaelides et al., 2005).

North Carolina macular dystrophy (NCMD, MCDR1) is a congenital autosomal dominant trait that appears to be completely penetrant. It is generally nonprogressive. The ophthalmoscopic findings are highly variable and are always much more dramatic than one would predict from the relatively good visual acuity level, which ranges from 20/20 to 20/400 (median, 20/60). Patients may have only a few drusen in the central macular region (grade I), confluent drusen confined to the central macular region (grade II), or a severe macular coloboma/staphyloma (grade III) involving 3 to 4 disc areas of the central macular region. Choroidal neovascular membranes develop in some patients. Color vision is normal. Electrophysiologic studies are also normal (summary by Small, 1998). Genetic Heterogeneity of Retinal Macular Dystrophy MCDR2 (608051) is caused by mutation in the PROM1 gene (604365) on chromosome 4p15. MCDR3 (608850) is caused by a duplication on chromosome 5p15. MCDR4 (619977) is caused by mutation in the CLEC3B gene (187520) on chromosome 3p21. MCDR5 (see 613660) is caused by mutation in the CDHR1 gene (609502) on chromosome 10q23. See MAPPING for possible additional loci for MCDR.

Spondylometaphyseal dysplasia with cone-rod dystrophy (SMDCRD) is characterized by postnatal growth deficiency resulting in profound short stature, rhizomelia with bowing of the lower extremities, platyspondyly with anterior vertebral protrusions, progressive metaphyseal irregularity and cupping with shortened tubular bones, and early-onset progressive visual impairment associated with a pigmentary maculopathy and electroretinographic evidence of cone-rod dysfunction (summary by Hoover-Fong et al., 2014). Yamamoto et al. (2014) reviewed 16 reported cases of SMDCRD, noting that all affected individuals presented uniform skeletal findings, with rhizomelia and bowed lower limbs observed in the first year of life, whereas retinal dystrophy had a more variable age of onset. There was severe disproportionate short stature, with a final height of less than 100 cm; scoliosis was usually mild. Visual loss was progressive, with stabilization in adolescence.

Cone-rod dystrophy is a retinal disorder with predominantly cone involvement. Rod impairment may occur at the same time as the cone impairment or appear later. Patients with CORD usually have reduced visual acuity, photophobia, and color vision defects (summary by Huang et al., 2013). For a discussion of genetic heterogeneity of X-linked cone-rod dystrophy, see 304020.

Leber congenital amaurosis-12 (LCA12) is characterized by congenital nystagmus, low vision, sluggish pupillary reflexes, absence of ocular pursuit from birth, early onset and long-lasting digitoocular signs of Franceschetti, and mild to moderate hyperopia. Photoaversion is usually present. Visual acuity, when measurable, is reduced to counting fingers, hand movements, or light perception (summary by Perrault et al., 2013).