Problems Inside The Eye

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What The Lenses Do

The lenses focus light onto the surface of the retina. In youth they are flexible and crystal clear. Aging naturally changes the lenses. They become hardened and hazy or "sclerotic". Injuries or disease may cause a lens to slip from its moorings (luxate), falling forward or backward into the fluid of the anterior or posterior chambers. As a result of either disease or inheritance the lenses can become opaque, becoming cataracts.

Nuclear Sclerosis

This is the most common eye "disorder" of pets, simply because it is not a disorder, it is a normal aging change. Over time the middle of the lenses becomes harder and more dense. In pets eight years old and older, this hardness begins to reflect light rather than refract it through to the retina. The result is an ever increasing blue-grey appearance to the lenses. It is easy to mistake this for cataract development.

Cataract

A cataract is a loss of transparency to part or all of the lens. It may be mildly foggy or completely opaque, only in part of the lens or filling it completely. A complete cataract creates a crystalline white lens with a slight yellow tint. While most canine cataracts develop as a result of inheritance, in cats, metabolic disease, specifically sugar diabetes, it the most common cause cataract formation. Cataracts are suspected either when opacity is seen in the lenses or when it is noticed that vision appears to be failing.

Diagnosis and treatment

Diagnosis is confirmed by ophthalmoscopic examination. Diabetic cataracts can develop in weeks and may even be the first indication to an owner that a pet has become diabetic. Surgery is considered when a pet is blind or on the verge of blindness. There are many surgical methods for removing cataracts, including phacoemulsification, but surgery is only undertaken when it is likely to restore or significantly improve vision. We will examine the retina by electroretinography to ensure it is functioning well before cataract surgery is undertaken. While it is normal that we have an artificial lens inserted to replace the cataractous lens, this is not always possible with our pets.

Lens Luxation And Subluxation

Trauma, from fights to road traffic accidents, inflammation to the anterior chamber of the eye, glaucoma, simple aging and inheritance all are known causes of either partial (subluxation) or complete (luxation) lens position changes. Complete luxation can be painful when it causes glaucoma. The white rim around the cornea (sclera) becomes inflamed. The cornea may become hazy or opaque. Partial luxation is more difficult to diagnose. It may only cause mild inflammation and increased tear production.

Diagnosis and treatment

The condition is diagnosed by clinical examination. A fully luxated lenses should be surgically removed as soon as possible to save remaining vision. Subluxations are usually treated with medications such as corticosteroids to reduce associated inflammation.

The Iris And Anterior Chamber Of The Eye

This is the region of the eye most affected by disease conditions elsewhere in the body. The iris may become inflamed (anterior uveitis) when any of these diseases occur elsewhere in the body.

Anterior Uveitis

The iris controls the size of the pupil. The ciliary body produces the fluid that fills the anterior chamber. Inflammation of the iris and ciliary body is called anterior uveitis. This is a painful condition. The pupil usually constricts and this is associated with squinting, excess tearing and avoiding light. The signs of anterior uveitis are similar to those of glaucoma. While the cause is variable it is often associated with immune system substances.

Diagnosis and treatment

Ocular pressure is measured to differentiate this condition from glaucoma. Immediate treatment usually involves pain control and suppression of the immune system with topical and systemic corticosteroids. Atropine may be used to dilate the pupil. An underlying condition is assumed when this condition affects both eyes. Anterior uveitis often develops into glaucoma.

Increased Pressure In The Eye (Glaucoma)

Although the fluid contents of the eye seem fixed, as if in a balloon, in fact there is an ever present slow exchange of fluid from inside the eye into the general circulation. Eye fluid is produced by the ciliary body. It slowly disperses from the eye into tiny veins where the iris meets the cornea. If fluid is produced faster than it is removed, pressure builds up in the eye. This is called glaucoma, and it is very painful.

Secondary glaucoma develops as a consequence of trauma or other eye diseases such as anterior uveitis. As well as pain, early glaucoma causes squinting, excess tearing and avoidance of light. A pet with glaucoma often has a fixed stare. At this stage there may be no visible enlargement of the eyeball but it is harder to the touch. Later the eyeball swells and obviously protrudes from the socket. By then a pet is blind in that eye.

Diagnosis and treatment

We diagnose by monitoring pressure inside the eye. Immediate, early treatment with drugs to lower intraocular pressure is vital if sight is to be saved. Laser surgery may be appropriate to partly destroy the ciliary body, reducing intraocular fluid production.

Once blindness develops, a glaucomatous eye is best removed, to eliminate pain or further injuries. Removing an eye sounds terrible but it makes a dpet much more comfortable and once hair regrows is also aesthetically very acceptable.

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