Corneal lipid (cholesterol) deposits are common in dogs and uncommon in cats. In dogs, there are 3 main causes:
An inherited condition called corneal dystrophy. This is usually noticed initially just in one eye but eventually progresses to affect the second eye. The appearance varies between breeds but most commonly these are cloudy spots in the center of each eye. It is quite rare that they progress to a point where there is significant vision loss. If this occurs in a dog to be used for breeding, the condition could be passed on.
Commonly affected breeds include the Cavalier King Charles Spaniel, Siberian Husky, Shetland Sheepdog, Collie and Beagle. This condition is usually non-painful though occasionally, particularly in Shelties, it can cause episodes of pain and chronic medical therapy (or even surgery) is sometimes indicated.
Corneal degeneration. If there is chronic irritation of a cornea, one of the ways it can respond is to degenerate. Part of the degenerative process can include deposition of cholesterol. In this situation, the problem usually affects just one eye, is associated with another eye problem, and there is usually inflammation (blood vessels) in the affected region of cornea. The best treatment in this case is to address the underlying cause.
Corneal degeneration is common in geriatric dogs. In this instance, the lipid deposits are usually associated with an even greater mineral component. This can be a greater problem if there are health problems, such as kidney disease, causing problems with calcium and phosphorus levels. Blood work might be recommended to help evaluate the problem. In the geriatric pets, ongoing medical therapy is usually needed in the advanced stage. Sometimes a deep piece of degenerated cornea will be sloughed from the eye resulting in a serious corneal ulcer. This can necessitate intensive medical therapy and/or surgery to save the eye.
When cholesterol deposits are found in cat corneas, they are usually due to degeneration that results from a chronic herpesviral infection.
The last main type of corneal lipid deposition is lipid keratopathy that can occur due to a high blood cholesterol level. In other words, the eye problem is the result of a systemic (generalized) health problem. For example, hypothyroid dogs can have very high blood cholesterol levels. Sometimes this first manifests in the eye(s) as corneal opacities. It usually affects both eyes but might initially show up in just one eye. Besides hypothyroidism, other underlying causes include Cushing's Disease, diabetes, inherited problems with lipid metabolism (e.g., Miniature Schnauzers), and even high-fat diets.
Remember that health problems do commonly first show up in eyes as this is the one part of the body we can see directly into. Therefore, just because your pet is still acting healthy at this point does not mean that there are no other problems.
The most important thing is to have a proper diagnosis as to a) if that is lipid in the cornea, and then b) WHY it is present. Many dogs have these fatty deposits and function just fine with minimal, if any, effect on vision. However, without proper diagnosis so that any underlying causes can be addressed, the eye(s) can get worse, vision can decline, and other signs of illness can arise.
If there are any questions about your pet's diagnosis, please let us know.