|By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com
Most diabetic dogs will develop cataracts and go blind. This FAQ is designed to assist the owners of diabetic dogs in knowing what to expect and to make decisions regarding cataract surgery.
What is a Cataract?
A cataract is an opacity in the lens of the eye. The entire lens may be involved or just a part of it. The patient will not be able to see through the opacity.
Why do Diabetic Dogs get Cataracts?
The lens of the eye is round, hard, and normally as clear as glass. Looking at the lens it is hard to believe it is a piece of living tissue. The lens is suspended by fibers that can adjust its position so that one can focus. The lens is encased in a capsule and depends on eye fluids for nutrients. The lens does not receive a direct blood supply.
Normally, the lens absorbs glucose from the eye fluids, using most of this for its own energy needs. Some of the excess is converted to another sugar called sorbitol. When there is excess sugar in the eye fluids, excess sorbitol is produced. Sorbitol pulls water into the lens, which in turn disrupts lens clarity and causes the cataract. Fructose is also produced from the excess glucose and contributes to this water absorption.
Cataracts do not necessarily imply poor diabetic control. Even well controlled dogs still can get cataracts.
How Long does it Take to go Blind?
Generally the cataract has matured and the dog is blind in a matter of weeks.
What Does it Mean to say that a Cataract is Mature?
A cataract’s maturity is determined by how much visual impairment there is felt to be. Since we cannot ask a dog to read an eye chart, we must determine this by a visual inspection. A light is used to look into the eye and view the colorful area at the back of the eye called the tapetum. (This is the area that flashes or appears colored in certain lighting.) 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 obstructs the entire tapetum. Ideally a cataract is removed in the early immature stage for the lowest surgical complication rate.
When a cataract is hypermature, it is starting to liquefy and dissolve. While this can lead to restoring vision, which sounds like a positive turn of events, it isn’t positive because the dissolution process is quite inflammatory.
All cataracts do not progress all the way to hypermature and may stay static or progress at changing rates; however, diabetic cataracts are notorious for reaching hypermaturity and creating inflammation.
What is Uveitis?
Uveitis is inflammation of the eye’s uveal tract, which consists of the eye's vascular (blood vessel) tissues. In simpler terms, uveitis is the inflammation that results when the hypermature cataract begins to liquefy. Uveitis is painful and tends to cause the eye to become reddened and the pupil to constrict. When uveitis is seen prior to surgery, success - defined as pain-free vision - is seen in only 50% of cases 6 months after surgery, as opposed to 95% of cases for which there was no uveitis before the surgery.
Is it Cruel to keep a Dog Blind?
Not at all. Dogs do not depend on vision the way humans do. A blind dog can get along very well as long as the furniture isn’t moved and the dog is properly supervised.
For tips on helping a blind dog adapt: www.ehow.com/how_7562_live-with-blind.html
There are many medical conditions that render a dog blind and as long as the condition is not painful, the dog can live a normal life as a successful and happy pet.
Cataract Surgery: What is the First Step?
The first step is a consultation with your regular veterinarian. Your dog’s diabetes must be well regulated before surgery is considered. If pre-operative lab tests show nothing that would not permit anesthesia, the next step is a referral to a veterinary ophthalmologist. Your regular veterinarian can set up the referral for you.
What Happens at the Ophthalmologist's?
It is necessary to determine if the eye will have vision after cataract surgery. There is, after all, no point to performing this surgery if the eye is going to be blind anyway. The most important test is called an ERG (an electroretinogram). This test checks the retina for electrical activity that, if present, indicates the eye should be able to see after the cataract in front of it is removed.
In addition to performing the ERG, the ophthalmologist will check for uveitis. Uveitis should be treated prior to surgery to minimize the inflammation that is inevitable after surgery.
What Kind of Surgical Procedures are Done?
There are two types of surgery: lens extraction and phacoemulsification. With lens extraction, the incision tends to be larger, the post-operative inflammation is greater, and the potential for leaving bits of lens behind is also greater.
With phacoemulsification, an ultrasonic instrument is used to liquefy the lens and a type of vacuum cleaner is used to suck out the lens. This procedure is more difficult if the patient is older as the lens has a harder consistency. This is the preferred method for diabetic patients.
After either surgery, an artificial lens is usually placed for optimal post-operative vision.
What Kind of after Care is Needed?
The patient will need to wear an Elizabethan collar after surgery to protect the eye. Cortisone eye drops are needed, probably for several weeks. Oral anti-inflammatories will be needed for weeks to months. Drops to keep the pupil dilated will also be used.
What Kind of Complications are Possible?
Complications to consider are:
- Long-term uveitis (probably of most concern for diabetic patients)
- Opacification of the lens capsule (usually correctable with laser)
- Corneal clouding (can be managed with 5% saline eye drops 4 to 6 times daily)
- Bleeding into the eye
- Retinal detachment (particularly if the cataract is hypermature)
Should Surgery be Done on both Eyes?
It is important to remember the old saying that the one-eyed man is king among the blind. A dog need only have one cataract removed to have vision restored. Doing both eyes is an option to discuss with the ophthalmologist as some dogs need all the vision they can get.
Cataract surgery requires committed patient care both in the hospital and at home.
Surgery also requires a financial commitment (which varies regionally and between different practices); your regular veterinarian can get a sense for average costs in your community when you are ready to consider restoration of your dog’s vision.