Pellucid marginal corneal degeneration is a bilateral disorder characterized by thinning of the cornea in the inferior periphery. The ectatic cornea remains clear and develops high, irregular astigmatism. We report the clinicopathologic features of three cases and review the clinical, histopathologic, and electron microscopic features of previously reported cases. Pellucid marginal corneal degeneration may represent an eccentric form of keratoconus and, in the setting of healed hydrops, may resemble closely Terrien's marginal degeneration clinically and histopathologically
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