A corneal arcus is a lipid deposition mainly consisting of cholesterol and phospholipid. Its prevalence varies in different populations and races, increases with age and is greater in the male. Earlier studies related the presence and severity of a corneal arcus to plasma lipid levels and linked it with certain familial hyperlipidaemias. The recent reclassification of such disorders in terms of hyperlipoproteinaemia now links the premature occurrence of an arcus with familial Type II and III hyperlipoproteinaemia. Other rare plasma lipid disorders in which corneal opacities occur are Tangier Disease and lecithin:cholesterol acyl transferase deficiency.