Corneal Dystrophy

Summary

Corneal dystrophy is a non-inflammatory opacification (clouding) of the cornea (the clear outer surface of the eye). Depending on the degree to which the cornea is affected, blindness may result, as both eyes are always involved.

While it's, by definition, considered a genetic disease in both dogs (commonly) and cats (rarely), the mode of inheritance is not known for all those that suffer it. For breeds have been well studied with respect to this trait, how it's inherited tends to differ.

It's also the case that there are varying versions of corneal dystrophy: 1) one is associated with abnormality of the upper (outer) surface of the cornea (the epithelium) 2) one is caused by fat deposits within the middle layer of the cornea (the stroma), and 3) one results in degenerative change of the lowest (deepest) layers of the cornea (the endothelium).

Pets can be affected as early as four months or as late as 13 years, with the age of onset depending on the breed-specific version of the disease.

Symptoms and Identification

A localized, grayish- or bluish-white, crystalline or metallic-looking cloudiness of the cornea is the first sign. The lesions can appear as round, oval or donut-shaped areas in the center of the cornea or close to the periphery.

Depending on the location of the clouding within the layers of the cornea and the severity of the disease, corneal dystrophy may progress to blindness or even corneal ulceration, sometimes resulting in severe pain and the loss of the eye. Otherwise, pain is not a component of the disease.

When diagnosing this disease, it's important to distinguish it from corneal diseases that have a similar appearance but are non-genetic, inflammatory or purely degenerative in origin. Consequently, a veterinary ophthalmologist is typically enlisted to render a specific diagnosis of corneal dystrophy.

Affected Breeds

The slower-progressing forms of the disease are more common in:

• Cocker Spaniel

• Poodle

• Samoyed

• Siberian Husky

• Pointer

• German Shepherd

• Bichon Frise

The faster-moving, more severe forms of the disease are more common in:

• Airedale Terrier

• Boston Terrier

• Chihuahua

• Dachshund

• Manx cats have also been found to suffer a genetic predisposition to corneal dystrophy.

Treatment

No treatment has been found to cure this disease process. It is relentlessly progressive and cannot be halted, though many attempts have been made to limit the spread of the opacification through drugs, corneal surgery and dietary changes, though all have proven only mildly effective, if at all.

Pets who suffer the corneal ulceration that may occur in some corneal dystrophy cases may be treated with a variety of drugs including antibiotics and other ophthalmic preparations but these, too, are often progressive and difficult to prevent or manage. Enucleation, or eye removal, is sometimes a necessary treatment for these patients.

Veterinary Cost

The cost of ophthalmologist assessment varies from $100 to $250. Treatment of a hard-to-treat ulcer can range from $300 for basic management to more than $3,000 if surgery is required to save the eye. Eye removal is typically a $500 to $1,500 procedure.

Prevention

There is no means of prevention save through breeding programs that exclude affected dogs and their first-degree relatives. Sadly, because the lesions in some breeds do not appear until later in life, it becomes difficult to restrict the breeding of dogs in which the disease has not manifested.

References

Cooley, P.L. and Dice, P.F.: Corneal dystrophy in the dog and cat. Vet Clin No Am 20:681-692, 1990.

Whitely, D.: Canine cornea. In. Gelatt KN, editor. Veterinary Ophthalmology 2nd ed. Pages 307-356; 1991.

Dice, P.F.: Corneal dystrophy in the Airedale. Proc Am Coll Vet Ophthalmol. 7:36, 1976.

Waring, G. O.; MacMillan, A; Reveles, P.: Inheritance of crystalline corneal dystrophy in Siberian Huskies. J Am Anim Hosp Assoc 22:655, 1986.

Dice, P.F.: Corneal dystrophy in the Shetland Sheepdog. Am Coll Vet Ophthalmol, 15:241, 1984.

Ekins, M.B.; Waring, G.O.; Harris, R.R.; et.al.: Oval corneal opacities in Beagles, PartII: Matural history over 4 years and study of tear function. J Am Anim Hosp Assoc 16:601, 1980.

Dice, P.F.: Corneal endothelial-epithelial dystrophy in the dog. Am Coll Vet Ophthalmol 7:36, 1976.