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Fish eye disease is very rare; about 30 cases have been reported to date. Fish eye disease seems to be less common than familial LCAT deficiency (see this term).

Corneal opacities are progressive and are observed from an early age (adolescence or young adulthood) and sometimes result in visual impairment. These lesions are generally more severe than in complete LCAT deficiency (familial LCAT deficiency, see this term) and form a mosaic pattern of small dot-like grey-white opacities. Signs of atherosclerosis have only been reported in rare cases although patients have low HDL cholesterol levels. Hepatomegaly, splenomegaly and lymphadenopathy are generally not present.

18 different mutations in the LCAT gene (16q22.1), encoding the LCAT enzyme which catalyzes the formation of cholesterol esters in lipoproteins, have been identified in FED cases. In patients with this disorder, alpha-LCAT activity (i.e., the activity of LCAT in esterifying cholesterol within HDL) is abolished, but beta-LCAT activity (i.e., the activity of LCAT in esterifying cholesterol within other lipoproteins) is preserved. Impaired enzyme function is thought to result in deposition of lipids in the cornea.

Initial diagnosis is suspected on the basis of corneal clouding. Definitive diagnosis requires molecular genetic testing of the LCAT gene and functional analysis of the gene product.

Differential diagnosis includes Schnyder corneal dystrophy as well as familial LCAT deficiency and Tangier disease (see these terms).

Prenatal diagnosis is possible.

FED follows an autosomal recessive pattern of inheritance. Genetic counseling should be offered to affected families.

Treatment is symptomatic. Severe visual impairment may require corneal transplantation.

Morbidity is related to progressive corneal opacification, which may lead to visual impairment.