Acute corneal hydrops occurs in approximately 3% of patients with keratoconus. Although most cases of hydrops are associated with keratoconus due to the prevalence of the disease, the incidence of hydrops is actually higher in other corneal ectatic disorders such as pellucid marginal degeneration and keratoglobus, with some reports being as high as 11% [1-2].
The term « forme fruste keratoconus (FFKC) » was first proposed by Amsler in 1961, and then refined by Klyce et al. to define the apparently normal contralateral eye in unilateral KC, the forme fruste being « an incomplete, abortive, or unusual form of a syndrome or disease ».
Pellucid marginal degeneration (PMD), is a degenerative corneal condition, often confused with keratoconus. It is typically characterized by a clear, bilateral thinning in the inferior and peripheral region of the cornea, although some cases affect only one eye.