Symptoms
Confusion often arises over the use of the term "corneal dystrophy" in dogs. Technically, "corneal dystrophies" are diseases of the cornea that are bilateral, non-inflammatory and inherited. The confusion arises because the term "corneal dystrophy" is sometimes used to refer to a disease with similar clinical signs but is not hereditary. A more appropriate term for the non-inherited conditions is corneal degeneration. In most breeds, corneal dystrophy appears as gray-white, crystalline or metallic opacities in the center of the cornea or close to the periphery. These opacities may affect any layer of the cornea, the epithelium (outer layer), the stroma (the thick, middle layer), or the endothelium (the inner layer). The opacities are usually oval or round and are sometimes doughnut-shaped. The age of onset of the disease varies within and among dog breeds and may range from 4 months in Airedale Terriers, to up to 13 years in Chihuahuas. The opacities usually progress but in some cases they remain static. Their progression may be very slow and may or may not lead to blindness (common in Cocker Spaniels, Poodles, Samoyeds, Siberian Huskies, Pointers, German Shepherds, and Bichon Frises). On the other hand, progression may be rapid and lead to blindness (more common in Airdale Terriers, Boston Terriers, Chihuahuas and Dachshunds). The mode of inheritance varies among breeds and in many breeds it is unknown. In the Airedale Terrier it is thought to be a sex-linked trait and in the Siberian Husky, Corneal Dystrophy has been shown to be a recessively inherited trait with variable expression.
Corneal dystrophies are usually not painful. In a few breeds, however, a dystrophy can lead to secondary breaks in the epithelial (outer) layer of the cornea. When this occurs a painful corneal ulcer develops requiring intense treatment. In other breeds, a painful ulcer may not develop and the dystrophy itself is not treatable. No medication will "dissolve" the opacity. Surgical removal of the dystrophic area may temporarily decrease the opacity in cases of epithelial dystrophy. Often, however the opacities will reform in the healed cornea.
