Twenty-nine Finnish patients (8-80 years old during follow-up) with hyperornithinemia and gyrate atrophy (HOGA) were followed 2 to 31 years to determine when and how rapidly visual acuities and visual functions were affected by the disease. Considerable variability was observed both in the age at which visual acuities began to decrease and the age at which visual acuities reached 20/200. Acuities in phakic eyes tended to decrease from 20/30 to 20/200 in ten years or less, while aphakic eyes exhibited generally slower loss of vision. Without benefit of cataract surgery, the percentage of eyes with acuity 20/200 or worse would have been 37% at age 30 and 64% at age 40, but through surgery actually performed was 20% at age 40. Constriction of visual fields with age was marked and correlated well with diminution in dark adaptation.