Corneal lipid degeneration is the deposit of fatty material within the cornea. It is usually secondary to other ocular or systemic disorders and may be a unilateral (one-sided) or bilateral (both sides). Clinical appearance may be highly variable; lipid infiltrates are often dense white, grayish-white, or crystalline with sharply demarcated borders.
Corneal lipid degeneration is more common in dogs than cats and may affect any age or breed.
Causes
Spontaneous inherited disorders or dystrophies of the cornea. These are spontaneous depositions of lipids in the cornea that occur in both eyes and have no apparent underlying cause. This form of lipid degeneration occurs in over 20 different breeds of dogs, including the Siberian husky, beagle, American cocker spaniel, King Charles cavalier spaniel, and German shepherd dog. The age of onset varies depending upon the breeds, and the surrounding cornea is usually normal.
High circulating cholesterol levels may result in fatty infiltration of the cornea. Usually these high circulating levels of cholesterol are associated with hypothyroidism, in which the thyroid gland does not produce enough thyroid hormone.
Active or prior inflammation of the cornea may result in lipid degeneration. The exact mechanism for this lipid infiltrate is unknown, but it may occur following dry eye, certain forms of corneal inflammation (such as pannus), and inflammation involving the interior of the eye, particularly anterior uveitis.
What to Watch For
Uveitis (inflammation of the eye)
Diagnosis
Complete eye examination with Schirmer tear test, fluorescein staining of the cornea and examination of the interior of the eye
Complete physical examination
Complete blood count (CBC) is typically normal
A fasting biochemical profile may reveal elevated cholesterol levels. If high cholesterol is found, then thyroid tests are indicated
Treatment
There is no effective medicine available to decrease or prevent the development of lipid within the cornea, but any corneal or ocular inflammation present should be treated appropriately. Surgery is not recommended to remove the lipid because the infiltrate usually returns to the cornea after surgery.
If high cholesterol is detected, then the amount of fat in the diet is reduced. Although reduction of the high cholesterol may prevent further deposition of lipid in the cornea, it does not often clear the lipid already present in the cornea.
Thyroid hormone supplementation is started if hypothyroidism is diagnosed.
Home Care and Prevention
It is very important to follow the instructions given to you by your veterinarian. Reexamination is indicated if ocular pain or corneal ulceration develop, to monitor any ocular inflammation present, and to monitor response to therapy for hypothyroidism.
The best way to prevent corneal degeneration is to control underlying or associated diseases. It is recommended that dogs with the inherited, spontaneous corneal dystrophies not be used for breeding.
In most instances, lipid degeneration of the cornea is not painful and does not significantly decrease the dog's vision.
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