The eye in metabolic diseases: clues to diagnosis

Ophthalmologic manifestations occur in various inborn errors of metabolism (IEM), including small molecule disorders and organelle disorders. In a minority of diseases the occurrence of eye abnormalities could be attributed to direct toxic mechanisms of abnormal metabolic products or accumulation of normal metabolites by errors of synthetic pathways or by deficient energy metabolism. The age of onset of ocular abnormalities in IEM is variable, but onset often begins from birth to childhood. The major IEM associated with eye abnormalities include errors of lipid metabolism, carbohydrate metabolism, protein metabolism, and metal metabolism. IEM disorders with ocular motor manifestations include lipid storage diseases, neurotransmitter disorders and respiratory chain disorders. The purpose of this article is to describe ocular phenotypes associated with IEM, focusing on those diseases in which the ocular involvement is seen relatively early in the course of the disease. As therapeutic approaches become available for certain groups of IEM, the need for early diagnosis is increasingly important.