What are the clinical signs of corneal lipidosis?
Lipid deposits in the cornea appear as well-defined areas of sparkly, shiny, or crystalline material. When lipidosis is due to corneal degeneration, other clinical signs may include inflammatory indicators such as eye redness or cloudiness in the eye.
( via Wikimedia Commons / Joel Mills (CC BY-SA 3.0.)
Diagnosis is based on a thorough eye examination, including fluorescein dye application, and Schirmer tear test; blood tests, age, breed, and your pet’s history. If your veterinarian suspects hyperlipidemia, then fasting cholesterol, triglyceride, and blood glucose level tests will be recommended.
Treatment for corneal lipidosis depends on the cause.
Corneal dystrophy does not require treatment. Your veterinarian will monitor your pet’s eyes periodically to watch for the development of corneal ulcerations.
Corneal degeneration requires treating the primary inflammatory condition in the eye which may include antibiotic or anti-inflammatory eye drops. Your veterinarian may also prescribe pain medication or artificial tear ointment to provide lubrication to the eye and comfort if the corneal surface is irregular.
Lastly, any condition that is causing an elevated cholesterol level must be treated directly in order to reduce the blood cholesterol levels. Dietary management, along with supplementation with additives to reduce cholesterol (flaxseed oil, oat bran, and niacin) can also be helpful in reducing the cholesterol levels.
If vision is affected or if corneal ulceration occurs multiple times, referral to a veterinary ophthalmologist is recommended.
Corneal lipid deposition secondary to a high concentration of systemic lipoproteins (lipoproteinemia) is the least common cause of corneal lipid opacification in dogs. Lipoproteinemia has also been associated with corneal lipid deposition in humans, rabbits, frogs, and rarely in cats. Experimentally, dogs fed a high fat diet do not significantly increase their corneal fat deposition, whereas obligate herbivores (e.g. rabbits) do. In dogs, corneal depositions associated with lipoproteinemia are typically ring-shaped and found within the perilimbal area. This characteristic opacification is therefore termed corneal arcus. In dogs, corneal arcus initially develops within the peripheral cornea beneath the third eyelid. All dogs with a corneal arcus have lipoproteinemia, but not all dogs with lipoproteinemia present a corneal arcus.
Corneal degeneration describes corneal lipid or calcium deposition secondary to ocular disease. In a dog, this type of lipid deposition is termed a secondary lipid keratopathy. Lipid accumulations are observed proximal to blood vessels, or in a fan-shaped opacity in advance of the vascular arcade. These deposits are typically unilateral, localized, and are associated with necrosis of corneal fibroblasts. Conditions associated with a secondary lipid keratopathy include ulceration, corneal rupture, keratoconjunctivitis sicca, episcleritis, chronic superficial keratitis, herpes keratitis, limbal tumorigenesis, surgical incision, and conjunctival grafting. Corneal degeneration can obstruct vision due to the size and/or position of corneal opacifications. Erosions of the corneal epithelia can also occur in these regions of opacification.
Corneal dystrophy is the most common cause of lipid deposition in the canine cornea. In dogs, with corneal dystrophy a defect in keratocyte metabolism is thought to result in an accumulation of lipids within corneal fibroblasts. This accumulation also increases the rate of corneal fibroblast cell death. Corneal dystrophy is bilateral and the accumulation of lipid is gradual. The resultant corneal opacities consist of cholesterol, phospholipids, and/or fatty acids (Figure 1). Breeds predisposed to corneal dystrophy include the beagle, Siberian Husky, Cavalier King Charles cocker spaniel, rough collie, Sheltland sheepdog, and Airedale. Treatment options include lubrication to retard the erosion of corneal epithelia, and limiting the fat content in a dog’s diet to less than 10%. As a genetic condition, owners are also discouraged from breeding dogs with signs of corneal dystrophy.
This is the second in a series of articles discussing the causes of corneal opacifications. There are several possible differentials for corneal opacifications that do not stain with fluorescein. These include corneal pigmentation, fibrosis, calcium or lipid deposition, cellular infiltration, the presence of a foreign body, sequestrum, and/or edema. This article will concentrate on corneal opacifications due to lipid deposition.
What does Arcus Senilis look like?
Arcus senilis is a gray or white arc visible above and below the outer part of the cornea — the clear, domelike covering over the front of the eye. Eventually, the arc may become a complete ring around the colored portion (iris) of your eye. Arcus senilis is common in older adults.