Cataract means opacification (whitening) of the lens of the eye. The lens is normally clear and lies just behind the iris, which is the colored part of the eye. The pupil is the hole in the iris that allows light into the back of the eye. The lens takes the light coming in and focuses it on the retina. The retina is like the film in a camera: it makes the picture that we see.
Cataracts in dogs and cats usually begin as small, white opacities in the lens. Because most of the lens is clear in the early stages, the patient will be able to see around these opacities. However, if the opacity becomes large enough to involve the entire lens, vision may be reduced or lost. Cataracts in dogs and cats can occur at any age. There are many causes of cataracts: heredity, toxic substances, trauma, and diabetes mellitus, to name a few. There is no way of preventing most cataracts and medical preventative therapy is still not available.
If cataracts are present in both eyes of a patient and are causing blindness. There are two possibilities for treatment. Medication can be used to dilate the pupils as widely as possible to allow more light into the eye. This sometimes provides enough stimulation to the retina that the patient can avoid obstacles. The alternative is surgical removal of the cataractous lens. Before surgery can be considered, the retina must be shown to be normal. This can be determined by direct observation if the cataracts are not dense. If observation is not possible then an electroretinogram (ERG) should be done. The ERG tests the electrical function of the retina as the electrocardiogram (EKG) tests the heart. If the retina is not normal, cataract removal would be pointless because the patient would still not be able to see.
If the retina is normal, surgery can be done. Although this works well in people, it is sometimes unsuccessful in other animals, particularly dogs and horses. Part of the reason for the lower success rate in dogs and horses is the tremendous inflammation caused by the surgery. The post-operative inflammation sometimes may lead to closure of the pupil, corneal scarring, or glaucoma, all of which can cause loss of vision. Medication is routinely given after surgery to decrease inflammation and prevent these problems from occurring. Despite potential post-operative complications, many animals do very well after surgery. Vision returns soon after surgery without the need of lens implantation as is necessary in people.
Most dogs and cats are able to get around fairly well with cataracts if their environment is not constantly changing. If this is not the case and you are considering cataract removal for your pet, we can recommend a veterinary ophthalmologist for consultation and surgery.
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