Corneal arcus, or arcus senilis, is most often an involutional change modified by genetic factors. However, arcus is sometimes indicative of a hyperlipoproteinemia (involving low-density lipoproteins) with elevated serum cholesterol, especially in patients under 40 years of age (see Chapter 11). It can be a prognostic factor for coronary artery disease in this age group. Arcus occurs occasionally as a congenital anomaly (arcus juvenilis), usually involving only a sector of the peripheral cornea and not associated with abnormalities of serum lipid.
Arcus is a deposition of lipid in the peripheral corneal stroma. It starts at the inferior and superior poles of the cornea and in the late stages encircles the entire circumference. The incidence is 60% in individuals between the ages of 50 and 60; it approaches 100% in individuals over 80. The frequency is higher in the black population. The arcus has a hazy white appearance, a sharp outer border, and an indistinct central border; it is denser superiorly and inferiorly (Fig 12-6). A lucid interval is usually present between the peripheral edge of the arcus and the limbus. The lipid is found to be concentrated mainly in 2 areas of the peripheral corneal stroma: one adjacent to Bowman layer and another near Descemet’s membrane. Unilateral arcus is a rare condition associated with contralateral carotid artery disease or ocular hypotony. Arcus is also seen in Schnyder central crystalline dystrophy.