Schlaeppi first introduced the term “pellucid” meaning translucent in 1957 to describe a clinical condition of the peripheral cornea with inferior thinning in the absence of neovascularization or lipid infiltration. Pellucid marginal degeneration (PMD) is an uncommon, idiopathic, noninflammatory ectatic corneal degene­ration. The condition frequently affects adults between the ages of 20 and 40 years. There is no gender predilection or family history. However, increased astigmatism in family members has been reported. Corneal topography may show various abnormalities in clinically normal appearing family members suggesting that corneal ectatic disorders may, in fact, represent a clinical spectrum. Histopathologic findings of the PMD corneas demonstrate stromal thinning and localized loss of Bowman’s layer. Collagen with 110 nm banding has also been found. Corneas from PMDs show reduced keratan sulfate pointing to the possibility that this may be a metabolic consequence of endothelial abnormalities.