Terrien marginal degeneration was first described by Terrien in 1990 as a bilateral, marginal ectasia of the cornea. This not-uncommon condition is now characterized as a slow-progressing, noninflammatory degeneration, initially presenting in the superonasal cornea. Though any age can be affected, literature suggests it appears primarily above the age of 40 and more commonly in men. Disease progression is classically slow, taking several years to develop. Patients are usually asymptomatic until continued thinning results in increased astigmatism and subsequent diminution of visual acuity. Perforations, either spontaneous or with minor trauma, are a serious consequence, but they are rare, with only a handful of reported cases.

Clinical hallmarks of Terrien marginal degeneration include ectasia and furrowing of the peripheral cornea with associated lipid deposition, as well as vascularization. Initial findings present as fine, white-yellow, punctate, stromal opacifications that appear similar to arcus senilis. Subsequent stromal thinning is heralded by the formation of a circumferential, gutter-like cavitation parallel to the limbus. In later stages, lipid deposition, visible as a solid white line, develops along the anterior edge ( Figure 1 ). This leading edge is steeply sloped, in contrast to the gradual slope of the posterior lip. Vascularization stems radially from the limbus and is located within the anterior stroma. An area of clear cornea can often be visualized between the leading edge of the gutter and the limbus. Pseudopterygia, at positions other than 3 o’clock and 9 o’clock, grow obliquely onto the cornea in approximately 20% of Terrien cases ( Figure 2 ). These pseudopterygia are thought to be characteristic of this condition and may occur in the earlier stages of disease, before marked thinning. Terrien degeneration typically presents bilaterally but can be very asymmetric between the 2 eyes. The superior cornea is primarily affected, but as the disease progresses, inferior cornea can also be involved.

Clinical features of Terrien marginal degeneration. Classic findings including peripheral thinning, superficial vascularization, and a leading edge of lipid deposition.

Pseudopterygium in case of Terrien marginal degeneration with ocular surface inflammation. Note the conjunctival injection in the area of the pseudopterygium.

The majority of patients with Terrien marginal degeneration lack signs and symptoms of inflammation. However, a variant form of the disease with prominent inflammatory findings has been identified by a number of investigators. Histopathologic examinations reveal an intact epithelium throughout the course of the disease, despite degeneration of the basal epithelial cells, and an abnormal appearance to the basement membrane. The Bowman layer and anterior stromal lamella are lost and replaced by vascularized connective tissue. Histiocytes that line the blood vessels have evidence of increased lysosomal activity and collagen deposition, consistent with a degenerative etiology. The Descemet membrane and endothelium are typically intact, though a number of reports have observed spontaneous ruptures in these layers, resulting in intralamellar dissection and intracorneal cysts ( Figure 3 ).

Intracorneal cyst in Terrien marginal degeneration, as a result of a break in the Descemet membrane.

Although the clinical and histopathologic manifestations of Terrien degeneration are well documented, the literature on this condition is relatively sparse, and the exact etiology of the condition remains obscure. Herein we present a larger, retrospective study describing the clinical characteristics and outcomes of patients diagnosed with the condition in a tertiary corneal clinic at the Toronto Western Hospital from 2004 to 2013. The purpose of the study is, in part, to confirm reported findings with a larger, more robust population, and to draw on any new conclusions that may help the practicing ophthalmologist understand this disease better.