Because pets adapt so well to being blind, it can be quite a challenge to tell what they can (and cannot) see. Typically, pets that lose their eyesight gradually (usually due to slowly arising conditions like cataracts, or Progressive Retinal Atrophy) will be adapting to lower and lower levels of vision and make a fairly smooth transition to blindness. These pets will have a mental map of their surroundings and be able to navigate their environment fairly well. Sometimes the first indication that something is wrong is when they bump into furniture that has been recently moved.
Pets that have a quick transition to blindness can show more obvious signs such as bumping into things, reluctance to walk, and with cats, an inability to judge distance and refusal to jump. More subtle signs include loss of confidence and, sadly, even aggression towards other pets or people if they’re startled.
Light enters through the surface of the eye (cornea), gets passed through the clear lens, and then is focused upon the retina(nerve tissue at the back of the eye). Any disease that affects the clarity of these structures potentially causes loss of vision. Diseases that affect both eyes are most likely to cause complete blindness.
The usually clear corneacan become opaque due to conditions causing heavy pigment deposits. This is most common in short-nosed dogs such as pugs, or in dogs that suffer from chronic dry-eye that has been left untreated.
When the lensbecomes cloudy, light cannot travel through it, and the eye will often appear white or “cloudy”. This opacity is called a cataract. There are many causes of cataracts. They’re hereditary in some dog and cat breeds but also caused by diabetes in dogs, or certain infections or inflammatory conditions in cats.
The retina can be affected by diseases such as Progressive Retinal Atrophy (PRA). This strikes older dogs and is hereditary in breeds such as the Labrador and Poodle. A different form of hereditary degeneration occurs in the Siamese cat. Other diseases of the retina include glaucoma, SARDS (Sudden Acquired Retinal Degeneration), and in cats, retinal hemorrhage caused by hypertension (high blood pressure).
Diseases of the braincan also cause blindness by impairing optic nerve transmission, or the processing of vision in the optic cortex of the brain.
In certain circumstances but certainly not all, blindness can be treated.
Cataracts can be removed via surgery if your pet is considered a suitable candidate. This is more common in dogs and rarely carried out in cats. The surgery is costly in terms of finances and in time. It requires a considerable commitment to postoperative care.
Retinal hemorrhage in cats can improve with treatment for hypertension, but less than 50% can regain some vision if treated.
Sadly, conditions such as PRA, SARDS, and many forms of glaucoma are irreversible.
Most pets will have a mental map of their living area. It may help to keep them restricted to a smaller area until they’re completely familiar with it, then extend their territory over time.
Additionally:
It’s very important to visit your vet, or veterinary ophthalmologist if you suspect your pet may be losing their vision. They will help make a diagnosis and determine any treatment options.
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