Chronic corneal edema in aged ranch mink.

Chronic corneal edema occurred in 53% of 116 ranch mink (Mustela vison) 8 to 11 years old. Most were royal pastel females, the main group at risk. Bilateral in 46 of 66 affected mink studied, the edema evolved over a month or so until the cornea became opaque, diffusely pale blue-gray or white, and greatly thickened. The swollen cornea did not become ulcerated, pigmented, or vascularized, even after it had been severely edematous for a year or two. The edema supervened as a consequence of spontaneous deterioration of the corneal endothelium. Attenuation and loss of the endothelial monolayer were the most common light microscopic changes. Other changes included discrete excrescences (guttata) along the posterior surface of the thickened Descemet's membrane and a subendothelial fibrillar or fibrocellular layer (posterior collagenous layer) often apposed to the excrescences. Likened to the primary endothelial dystrophies of man and the dog, this endothelial disorder of mink is regarded as an abiotrophic degeneration with its own distinguishing features in this species.