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A cataract is an opacity of the lens of the eye.   The lens is behind the iris (the brown or blue part of the eye) and can change its shape, allowing animals to see up close.   The lens is covered by a thin capsule, which is the consistency of cellophane.


In front of the lens is a clear fluid, aqueous, and behind it is a clear gel, the vitreous.   The vitreous helps keep the retina attached.   The retina is a layer of cells that functions similar to the film in a camera, i.e. it receives the light and allows the animal to see.

Cataracts may develop because of an inherited defect, with age or secondary to inflammation, trauma, diabetes or retinal degeneration.   As cataracts progress, they go through different stages, immature, mature and hypermature.   In the later stage, cataracts may leak proteins that cause inflammation inside the eye called uveitis.   Lens-induced uveitis is inflammation inside the eye.

A condition that appears similar to cataracts is called nuclear sclerosis.   This is a normal change that occurs in the lens of older animals.   Nuclear sclerosis appears as a slight graying of the lens.   It usually occurs in both eyes at the same time and occurs in older animals.   The loss of transparency occurs because of compression of the linear fibres in the lens.   This condition does not impair vision, other than making focusing on close objects more difficult.   Treatment is not required for this condition.

There is no effective medical treatment for cataracts.   When cataracts are caused by other diseases (e.g. diabetes, inflammations etc.) the primary disease itself should be treated.   As long as a cataract does not
impair vision, no treatment is necessary;  but when vision starts to deteriorate (e.g. poor night vision), surgical removal may be considered.

Cataract surgery involves removing the lens and the front part of the lens capsule.   The capsule in the back is usually left in place to maintain the normal arrangement of the structures in the eye.   Referral to a veterinary opthalmologist can be arranged, if requested.

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