Terrien marginal degeneration.

Terrien marginal degeneration, a rare disease resulting in peripheral corneal thinning, commonly occurs in middle-aged males and usually manifests clinically with decreased visual acuity from increased corneal astigmatism. Although the exact etiology is unknown, hypotheses focus on possible degenerative and inflammatory origins. Histopathologic studies often reveal characteristic findings of innumerable intracellular and extracellular vacuoles in the affected stroma. Distinguishing Terrien marginal degeneration from other peripheral corneal diseases such as Mooren ulcer and pellucid marginal degeneration is important. Nonsurgical interventions include spectacles, rigid gas-permeable contact lenses, and scleral lenses; however, when the corneal thickness is ≤150 μm, surgical interventions including tectonic grafting and lamellar keratoplasty may be necessary.