Occult macular dystrophy (OMD) is a rare inherited degradation of the retina, characterized by progressive loss of function in the most sensitive part of the central retina (macula), the location of the highest concentration of light-sensitive cells (photoreceptors) but presenting no visible abnormality. "Occult" refers to the degradation in the fundus being difficult to discern. The disorder is called "dystrophy" instead of "degradation" to distinguish its genetic origin from other causes, such as age. OMD was first reported by Y. Miyake et al. in 1989. Symptoms
Symptoms entail a loss of visual acuity in both eyes, including darkened vision, ring scotoma (ring of blindness close to the center of vision), color blindness, and difficulty with bright lights. The scotoma may cause text slightly away from the center of vision to disappear; the appearance would not be black (in early stages) but of the same color as the nearby background. Many lines of an Amsler grid would be faded or invisible to the patient. The area of invisibility on the Amsler grid spreads with time. Symptoms do not include headaches or eye pain. The loss of acuity tends to be symmetric between the eyes. Etiology
OMD that is caused by mutations of the retinitis pigmentosa 1-like 1 (RP1L1) gene (OMIM 608581) is called Miyakes disease. While the mutation is dominant, OMD may manifest more strongly and earlier in children than in the parent (anticipation). However, cases have presented with no mutation to RP1L1.
Unfortunately, their size is limited--too limited to hold the RP1L1 gene. Therefore, a non-viral approach would need to be developed for gene therapy to treat OMD. Since RP1 has the same size problem, a gene therapy for RP could have a spillover effect for OMD. A stem-cell approach might entail taking stem cells from the patient, editing the mutation with CRISR, and inserting the stem cells in the eye. However, as of 2014, researchers did not yet know if retinal stem cell surgery would work. Prevalence
Prevalence is unknown, but seems to be elevated in Asian populations, given that most OMD studies are of Japanese and Korean subjects. Given that Stargardts, the most common macular dystrophy, has a prevalence of 1 in 10,000 in the US,  the prevalence of OMD is likely well below 1 in 100,000. == References ==