41.1 Features

Gyrate atrophy (GA) of the choroid and retina is a rare, genetically determined, autosomal recessive, slowly progressive chorioretinal dystrophy characterized by sharply demarcated areas of chorioretinal atrophy in the midperipheral retina. This dystrophy was first reported in 1973, and more than 200 cases have since been described with about one-third from Finland. The main feature of this disease is the hyperornithinemia with levels 10 to 15 times above normal due to a deficiency of the mitochondrial matrix enzyme ornithine aminotransferase (OAT). Ornithine is a nonessential amino acid majorly converted to glutamate by OAT and subsequently to proline in the urea cycle. The OAT gene is located on 10q26 and found is expressed highly in the retina, liver, and kidney. Over 50 mutations have been described to date. OAT mutations lead to ornithine accumulation, which is toxic for ocular structures such as corneal endothelium, iris smooth muscle, ciliary body, photoreceptors, and especially the retinal pigment epithelium (RPE). The atrophic areas in the midperipheral retina show a marked loss of the choroidal vessels, including the choriocapillaris, RPE, and photoreceptors. The normally appearing areas in the posterior pole show focal areas of photoreceptor cell loss, shortening of outer segments in the transitional area, and absence in the atrophic areas.

41.1.1 Common Symptoms

Nyctalopia begins in the first and second decades of age (usually of mild and slowly progressive nature) and possible restriction of peripheral field vision. Visual acuity is usually preserved in the early stages but may decrease primarily from foveal involvement or secondarily from cystoid macular edema or cataracts. Blindness usually occurs in most untreated patients in the fifth decade of life.

41.1.2 Exam Findings

The fundus shows peripheral small, geographic, sharply demarcated enlarging and merging scalloped areas of atrophy of the RPE and choriocapillaris during the earlier and intermediate stages and a tendency for pigment clumping to occur at the margins of such lesions. Occasional patients have peripapillary atrophic lesions that progress in size in a similar way that progressive lesions do. Atrophy begins in midperipheral and peripheral areas, in a garland-shaped fashion, and then coalesces and progresses centrally and peripherally. In advanced stages, the disease involves the entire fundus, with relative sparing of the macula. The optic disc and retinal arterioles usually are normal until the late stages of the disease (▶ Fig. 41.1). Posterior vitreous detachment, epiretinal membranes, macular hole, choroidal neovascularization (CNV), and cystoid macular edema have been observed. Moderate to severe myopia is found in most patients. Posterior subcapsular cataracts generally appear in the second decade of life. Extraocular manifestations have rarely been associated with GA. The most common are electromyographic abnormalities, although very few patients complain of slight muscle weakness. Electroencephalograms or electrocardiograms also may be abnormal in some patients.

41.2 Key Diagnostic Tests and Findings

41.2.1 Optical Coherence Tomography

A fundamental tool to detect macular defects that are difficult to define with ophthalmoscopy. Hyporeflective cystic spaces secondary to macular edema (▶ Fig. 41.2), macular hole, epiretinal membrane, or vitreomacular traction have been described. Hyperreflective deposits could be seen in inner retinal layers, suggesting the gliotic response to ongoing cell death. Interestingly, in older GA patients, outer retinal tubulation corresponding to the arrangement of degenerating photoreceptor cells may be present.

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