Symptoms of Corneal Changes in Dogs
Corneal dystrophy and corneal degeneration are diseases of the cornea characterized by white, opaque mineral (either cholesterol or calcium) deposits within the cornea (the clear front part of the eye). The size, shape, and density of the areas of mineral deposits vary. Although these affected areas can be highly visible, they rarely cause blindness.
In cases of severe progression and discomfort, we can remove the mineral deposits through superficial keratectomy, a surgery in which the outer layer of the cornea and the mineral is removed; however, scar tissue may remain present instead of the mineral deposits. If a deep ulcer is found as a result of the degeneration, a grafting procedure may be necessary to allow the cornea to heal. Although most corneal dystrophy patients do not require surgical intervention, some pets will, and their owners should be aware of potential complications. Any surgical procedure can introduce complications, including potential anesthetic risks. Surgical procedures that involve the cornea seldom give rise to complications, which occur in less than five percent of these cases. Nevertheless, potential complications include, but are not limited to…
Corneal dystrophy may be an inherited trait in several breeds, including the Shetland Sheepdog, Siberian Husky, Beagle, American Cocker Spaniel, Miniature Schnauzer, and Airedale Terrier. Corneal dystrophy affects both eyes and occurs in dogs of any age. It has been reported to occur in dogs with high levels of cholesterol or calcium in their blood. Routine blood work can be performed to evaluate for these possible changes.
If the fluorescein stain does not show any abnormalities, the veterinarian will look for corneal stromal weakness (dystrophy), which affects both eyes, often affecting proportional focus. The cornea will be gray to white in appearance, with distinct margins. This disorder does not retain fluorescein stain and is not associated with inflammation of the eye. If an object has entered the eye (inflammatory cell infiltrate) it will cause the cornea to appear gray to white, with indistinct margins; microscopic examination of the corneal cells will reveal white blood cells, the cells that are responsible for defending the body against foreign materials and infection, indicating that organisms are present in the eye.
One of the main causes of corneal degeneration is lipid (fat) deposits in the supporting structure of the inner eyeball: the stroma and the epithelium. While lipids are a normal part of the body, being, as they are, a principal structure of living cells, hyper deposits of lipids in the tissues can bring about disorders to the system they are inhabiting. Systemic hyperlipoproteinemia, a metabolic disorder characterized by elevated concentrations of cholesterol and specific lipoprotein particles in the blood plasma, may increase the risk of deposits in the stroma, or may worsen already existing deposits. Hyperlipoproteinemia can be secondary to hypothyroidism, diabetes mellitus, hyperadrenocorticism (chronic production of too much cortisone), pancreatitis, nephrotic syndrome (a disorder in which the kidneys are damaged), and liver disease.
The cornea is the transparent lining that covers the external front of the eyeball; that is, the iris and the pupil (respectively, the colored area that expands and contracts to allow light in, and the lens that transmits the light and to the brain – the black center). The cornea is continuous with the white part of the eye, the sclera, which covers the rest of the eyeball. Beneath the cornea and the sclera is a layer of connective tissue that supports the eyeball from inside, called the stroma.
If a disease of the eye is present, your veterinarian will treat the condition accordingly. Lipid and calcium deposits that impair vision or create discomfort to the eye, either from a roughened surface, or from disruption and ulceration of the corneal epithelium, may benefit from a vigorous corneal scraping, or a superficial removal of part of the cornea (keratectomy). These procedures would be followed by medical management, since deposits are likely to recur in patients following superficial keratectomy surgery. Your dogs diet will also be a consideration. If hyperlipoproteinemia is diagnosed, a low-fat diet would be beneficial for hindering further progression. Your veterinarian will advise you on this. Both methods of treatment can be useful for slowing or stopping progression of the disease.
Your doctor will want to monitor your dogs serum cholesterol and triglycerides to assess the effectiveness of dietary management, if that has been recommended as a maintenance strategy. If a primary disease if present, its will be monitored for progression or regression, and treated according to the indications and comfort needs of your dog.