[Marginal pellucid degeneration of the cornea, or marginal keratoconus (author's transl)].

Histological and ultrastructural examination of the corneas of a woman presenting with marginal pellucid degeneration, treated by bilateral perforating keratoplasty, revealed obvious analogies with keratoconus. The condition of marginal pellucid degeneration is really only an excentric keratoconus. Marginal pellucid degeneration is a rare affection but it has been clinically sell defined. Many authors seem to have recognized it under various different names (cylindrical keratoconus, corneal protusion, piriform cornea). It is a pouch-shaped deformity of the cornea overlying a thinning of the linear stroma concentric to the limbus, always inferior and bilateral, perfectly transparent, non-vascularized, and without signs of corneal of conjunctival inflammation. The affection usually occurs in young adults.