Laurie Anne Walden, DVM
A cataract is an opacity in the lens, a small translucent structure just behind the pupil of the eye. The lens transmits light to the retina at the back of the eye. Because cataracts block light from reaching the retina, they can cause blindness. In some cases cataracts also lead to eye pain.
Cataracts are most common in older animals but also occur in young animals. An animal can have a cataract in just 1 eye or in both eyes at the same time.
Cataracts begin as small opacities that don’t have much effect on vision; the animal can see around them. Over time, some cataracts progress to involve most or all of the lens, reducing vision.
Cataracts commonly cause uveitis, or inflammation inside the eye. Uveitis can be uncomfortable. Cataracts can also cause lens luxation (lens slipping out of its normal position). Lens luxation increases the risk of glaucoma, which is painful and can also cause blindness.
Nuclear sclerosis of the lens is a normal aging change that looks similar to cataracts but doesn’t cause blindness or inflammation. The lens becomes more dense with age. In older animals, increased lens density makes the lens look cloudy, so the pupil appears bluish-gray instead of black. Unlike cataracts, nuclear sclerosis doesn’t block light, so it doesn’t interfere with vision.
Cataracts in dogs are often hereditary. Some of the many dog breeds that have hereditary cataracts are poodles, Havanese, Boston terriers, silky terriers, and cocker spaniels. Animals with hereditary cataracts should not be used for breeding.
Cataracts can also be caused by other conditions. Diabetes is a common cause of cataracts. Owners of a diabetic animal should know that their pet might go blind from cataracts. Cataracts can also be caused by trauma, inflammation, aging, toxins, and malnutrition. In many cases, the cause is not known.
An animal with a cataract usually has no symptoms (other than the opacity in the lens) unless the cataract blocks vision or causes uveitis. The signs of vision loss can be very subtle in animals, especially pets that live in environments that don’t change very much. Indoor pets know their way around the furniture and might not start bumping into things until they are nearly blind. Reluctance to jump up, navigating stairs more slowly than usual, and having a hard time finding food or the water bowl can be signs of impaired vision—or of other problems like arthritis.
The signs of uveitis caused by cataracts are also subtle and easy to mistake for other eye problems. Redness, drainage or discharge, and squinting are signs of eye discomfort from any cause. An animal with these signs should be checked by a veterinarian without delay.
Examination of the eye with an ophthalmoscope is used to diagnose cataracts, distinguish between cataracts and normal nuclear sclerosis, and look for uveitis and other problems within the eye. Blood and urine tests are used to diagnose diabetes and other conditions that can cause cataracts.
Small cataracts that don’t cause vision loss might not need to be treated right away, but they should be monitored. Even small cataracts can cause uveitis, and the earlier uveitis is treated, the better for the patient.
Cataracts are treated either medically or surgically. The aim of medical treatment is to keep the eye comfortable by managing inflammation and other complications. No known medical treatment can prevent a cataract from progressing to the stage of causing blindness.
Surgical removal of the lens is the only treatment that can restore vision in an animal that is blind because of cataracts. Lens luxation might also require surgical treatment. Before considering cataract surgery, veterinary ophthalmologists perform other tests to be sure the animal is a good candidate for surgery and doesn’t have other eye problems that might impair vision.
1. Gelatt KN, Mackay EO. Prevalence of primary breed-related cataracts in the dog in North America. Vet Ophthalmol. 2005;8(2):101-11. doi:10.1111/j.1463-5224.2005.00352.x
Photo by Ezequiel Garrido on Unsplash
Laurie Anne Walden, DVM
The contents of this blog are for information only and should not substitute for advice from a veterinarian who has examined the animal. All blog content is copyrighted by Mallard Creek Animal Hospital and may not be copied, reproduced, transmitted, or distributed without permission.