“Dear Dr. Gary, My dog has been diagnosed with diabetes for several years and recently started to bump into walls and furniture. My veterinarian said that my dog has ‘diabetic’ cataracts. Is there anything I can do to help my dog see? Thank you, Liz”
Like Liz, many owners face the challenges of taking care of a pet with diabetes and its complications. Here is some important information to help you to deal with cataracts in dogs.
The normal lens of the eye is translucent (clear) and it functions by transmitting light onto the back of the eye (retina). A cataract is any opacity in the lens of the eye, which will block the transmission of light to the back of the eye. The entire lens may be involved or just a part of it making vision difficult.
Cataracts in Diabetic Dogs
The lens of the eye is a living tissue that is hard and is normally clear like glass. The lens is suspended by fibers that can adjust its position to focus. It is encased in a capsule that depends on eye fluids for nutrients and does not receive a direct blood supply. Normally, the lens absorbs glucose from the eye fluids for it’s own energy needs.
The excess glucose is converted to another sugar, sorbitol that pulls water into the lens. The excessive fluid in the lens disrupts lens clarity and causes the cataract. Another sugar, fructose, is also produced and contributes to water absorption in the lens.
Cataracts do not necessarily imply poor diabetic control; even well controlled dogs get cataracts.
The maturity of the cataract is determined by how much visual impairment there is and since we cannot ask a dog to read an eye chart, we must determine this by a visual inspection. A bright light is used to look into the eye and view the tapetum, the colorful area at the back of the eye. In certain lighting, this is the area that flashes or appears colored, usually green.
When less than 10% of the tapetum is obstructed, the cataract is young and does not significantly change vision. When 10 to 50% of the tapetum is obstructed, this cataract is called early immature. When 51-99% is obstructed, the cataract is late immature. The mature cataract obstructed 100% of the tapetum. A hypermature cataract starts to liquefy and dissolve and can lead to restoring vision, which sounds like a positive turn of events but is not due to the inflammation it causes. All cataracts do not progress to hypermature and may stay static or progress at different rates; however, diabetic cataracts are notorious for reaching hypermaturity and creating inflammation.
Ideally, surgery is best performed when the cataract is removed in the early immature stage for the lowest surgical complication rate.
The first step is consultation with your primary veterinarian and your dog’s diabetes must be regulated before surgery is considered. After pre-operative testing is normal, referral to a veterinary ophthalmologist is the next step.
At the veterinary ophthalmologist, it is necessary to determine if the eye will have vision after cataract surgery. After all, there is no point to perform surgery if the dog is going to be blinds after. The test, ERG (electroretinogram) is performed to check the retina for electrical activity, that if present, indicated the eye should be able to see after surgery.
There are two types of surgery: lens extraction and phacoemulsification. The latter is the most preferred method for diabetic patients where an ultrasonic instrument is used to liquefy the lens and suction (‘vacuum cleaner’) device is used to suck out the lens. An artificial lens is usually placed for optimal vision after surgery.
A dog only needs one cataract removed to have vision resorted. Performing cataract surgery on both eyes is an option to discuss with the veterinary ophthalmologist.
Take Home Message
It is important to have all dogs with cataracts examined early to determine whether the cataract is secondary to other conditions such as diabetes, or inherited. Equally as important is to determine whether the cataract is affecting the eye, such as causing glaucoma or inflammation. Early evaluation by a board certified veterinary ophthalmologist allows appropriate therapy to be established for additional problems and allows a determination to be made as to whether the dog is a candidate for cataract surgery.
NOTE: Consult your veterinarian first to make sure my recommendations fit your special health needs.