[Important bilateral corneal astigmatism in a case of ocular ochronosis]

Ochronosis or alkaptonuria is a rare, autosomal recessive metabolic disease where the enzyme homogentisic acid 1,2-dioxygenase is missing. This enzyme is necessary in the oxidation of phenylalanine and tyrosine. As a result of this defect homogentisic acid, which is normally produced during the metabolism of the two amino-acids, cannot be further metabolized and therefore accumulates in the serum. It is massively excreted in the urine and as it is oxidized, the urine turns dark, a feature termed alkaptonuria. Tissue pigmentation called ochronosis is due to the presence and the chemical binding in the connective tissue of oxidized and polymerised products of homogentisic acid. The most important complications of alkaptonuric ochronosis as arthropathy are related to deposition of ochronotic pigment in the affected organs. In ocular ochronosis, the pigment is found in the sclera, conjunctiva, and limbic cornea. Vision is usually not impaired. We report the case of a man aged 73 years, with ochronosis, who developped a marked, late-onset bilateral astigmatism, related to this sclero-limbic ochronotic pigment. The clinical evolution, the result of histological examination and the physiopathology of this astigmatism are discussed.