Corneal Disease (Inherited) in Dogs

Inherited corneal disease, called corneal dystrophy, is a fairly common problem in dogs. About 20 breeds of dogs have some version of the disorder, but in most cases the mode of inheritance isn’t known. The cornea is the outer barrier of the eye that protects the anterior chamber, the pupil, and the iris. It is made up of the stroma in the middle, with a thin epithelial and endothelial layer on the outer and inner sides. Corneal dystrophy in dogs can affect different layers of the cornea. Dogs will develop irregular opaque patches of white or gray discoloration. These are often large oval or donut shapes, but sometimes the discoloration may appear as small white flecks. Most conditions are progressive, developing slowly over time. With the most common form of stromal dystrophy, dogs don’t experience discomfort or vision loss and no treatment is required. However, epithelial and endothelial dystrophies often cause blisters or corneal ulceration which can be painful, impair vision, and even result in blindness. The type of dystrophy and age of onset is usually breed specific. Corneal dystrophies are bilateral (affecting both eyes equally) and non-inflammatory. Secondary conditions that are not inherited (called corneal degeneration) can result from various eye diseases, inflammation or injury to the eye. Corneal degenerations can appear similar to dystrophies and are sometimes confused, but degenerations frequently only affect one eye.

Inherited corneal disease in dogs causes areas of discoloration on the cornea. Veterinarians call this corneal dystrophy. Many dogs don’t experience pain or vision loss, but in some breeds, corneal dystrophies can cause corneal ulcerations and even blindness.

These are some of the signs you might see in a dog with corneal dystrophy.

• Discolored area in the center of the eye
• Opaque grey or white area
• Round, oval, or donut shaped discoloration
• Swelling or excess fluid in the cornea
• Blue appearance to the eye
• Signs of eye pain (excessive tear production, squinting, scratching at the eye)
• Decreased vision

Types

Types of corneal dystrophies can be divided into what part of the cornea they affect.

• Epithelial (outer layer) is episodic erosion which may lead to corneal ulcers; breeds affected: Boxers, Shetland Sheepdogs
• Stromal (middle layer) is the most common type in dogs, sometimes called corneal lipidosis; in most breeds, progression is slow and symptoms are limited to discoloration; breeds affected: Siberian Husky, Cocker Spaniels, Poodles, Samoyeds, Pointers, German Shepherds, Bichon Frises (doesn’t usually cause vision problems), Airedale Terriers and Beagles (leads to impaired vision)
• Endothelial (inner layer) begins as excess fluid and painless swelling of the cornea; as the disease develops, painful blisters and ulcers often form and may lead to decreased vision and blindness; breeds affected: Boston Terriers (especially females), Chihuahuas, Dachshunds

Corneal dystrophies are an inherited disease. They are more common in specific breeds, but they could occur in any dog.

• In most breeds the specific genetic sequence hasn’t been studied 
• In Airedales, it is believed to be sex-linked, while in Siberian Huskies it is a recessive trait 
• Depending on the breed, dystrophies may become noticeable as early as 4 or 5 months (Airedale Terriers, Shetland Sheepdogs and Siberian Huskies) or as late as 9 to 13 years (Chihuahuas and Beagles)
• The majority of dogs become affected sometime in middle age (approximately 3-7 years)

Corneal degeneration is a non-inherited form of the disease that can occur secondary to some other problems.

• Corneal ulcerations
• Inflammation or injury to the eye (phthisis bulbi)
• Diseases which prevent the eye from closing (lagophthalmos)
• Overuse of NSAID’s

Your dog’s symptoms will help the veterinarian identify the problem, both discolored areas in the eye and signs of eye pain or decreased vision. Examination under a microscope will reveal deposits in the discolored area or a cloudy overall appearance. Fluorescein dye can help to identify ulcers or blisters. The veterinarian may need to test for other potential causes, like inflammation or infection, especially since some other acquired conditions may be more treatable.

Since dystrophies are inherited, your dog’s breed and family history will be necessary for an accurate diagnosis. Any history of eye disease or injury can also be relevant since these conditions may suggest the condition is an acquired degeneration. If your dog has used NSAID’s for an extended period of time, this can be another reason for a differential diagnoses.

For dystrophy with stromal deposits but no other symptoms, treatment usually isn’t necessary. The veterinarian may recommend frequent check-ups to monitor the condition.

Most treatments focus on eliminating the symptoms that cause discomfort for your dog. Medicated eye drops will be prescribed to treat erosion and ulcers in the epithelial layer of the eye. This can help to heal the lesions, but the problem may still recur periodically. If your dog has chronic severe problems, surgery may be necessary to remove the area of discoloration. The veterinarian will recommend a specialist ophthalmologist. In some cases, the discolored area may reform after surgery.

For edema (fluid retention) associated with the early stages of endothelial degeneration, the veterinarian may prescribe hyperosmotic drops to facilitate water removal. Medicated drops can also help heal ulcers and blisters as they form. For chronic problems, specialist surgical procedures are necessary. Thermokeratoplasty, a treatment that flattens the cornea, can sometimes help to eliminate the problem. You should discuss the risks and the likely outcome with your veterinarian or a specialist before deciding on any surgical treatment.

The most common types of stromal dystrophies don’t cause pain or vision problems and many dogs live long lives with this condition. The discoloration may get worse over time, but often no other symptoms are noted.

In some breeds that tend to develop ulcers, intermittent medical treatment and drops may be necessary to reduce pain and discomfort. If your dog experiences vision loss or blindness, you may need to manage this condition by helping him learn to get around without sight and blocking off any hazardous areas in your house, at least until he become accustomed to the new situation. Blind dogs can still live fulfilling lives.

If the veterinarian recommends surgical treatment, this may be a helpful option for your dog. In some cases surgery may completely eliminate the problem, in others you may still need to manage some symptoms after the operation. It’s a good idea not to breed any dog with corneal dystrophy, even if it’s a stromal dystrophy that isn’t causing a problem. Some offspring could inherit a more severe form of the disease and breeders prefer to reduce instances as much as possible.