Arcus senilis is a name applied to an opacity of the peripheral cornea occurring in persons of middle age or older. Generally separated from the limbus by a clear interval, it has a mat-white or yellow-white color and only when very dense does it contain scintillating crystals. The entire thickness of the corneal stroma may be involved but less extensively in the midstroma, and so the distribution of the opacity is usually that of an hour-glass. The most extensive involvement is that adjacent to the posterior surface (Descemet's membrane). While present to some extent in all persons past middle age, an arcus is also present occasionally in young persons (arcus juvenalis) and is particularly common in persons with familial hypercholesteremia and xanthomatosis.1-6 Its association with hypercholesteremia from other causes (myxedema, diabetes, lipid nephrosis) has been suggested but is equivocal.7-9 The opacity of the cornea occurring in the hypercholesteremic