What is a Cataract?
Like a camera, eyes have a clear lens inside them that is used for focusing. A cataract is any opacity within a lens. The opacity can be very small (incipient cataract) and not interfere with vision. It can involve more of the lens (immature cataract) and cause blurred vision. Eventually, the entire lens can become cloudy, and all functional vision lost. This is called a mature cataract. Some mature cataracts will transform over time into hypermature cataracts. Hypermature cataracts usually are reduced in size due to loss of water and proteins from the lens. This causes the lens to shrivel and the lens capsule to wrinkle—similar to a grape turning into a raisin. Hypermature cataracts vary in how cloudy they are. Some are completely cloudy, and others have clear areas that can allow some vision IF the rest of the eye is functional. Depending on the dog’s age and breed, it can take several months to years for a mature cataract to turn into a hypermature cataract.
All geriatric dogs (usually beginning at 6 years of age) develop a hardening of the lens (Nuclear Sclerosis) that causes the lens to have a grayish appearance. The grayish-blue haze increases as the dog ages. Nuclear sclerosis is NOT a cataract, and does not usually interfere with vision. The photo to the right shows a normal geriatric dog eye with normal nuclear sclerosis. Nuclear sclerosis also occurs in humans, and the hardening of the lens with age results in reduced near-vision in people; this is why people in their 40’s and older need reading glasses—because their lenses no longer are soft enough to easily change shape to allow for near vision. Another name for this is presbyopia, which means “old eye”. Dogs do not have good near-vision to begin with (compared to people), so nuclear sclerosis does not significantly interfere with their near-vision.
How do you tell the difference between nuclear sclerosis and cataract in your dog? The answer is that you can’t. You can start with having your family veterinarian evaluate your dog’s eyes, but often it is difficult for a doctor who is not an ophthalmologist to differentiate between the two conditions. However, veterinary ophthalmologists can tell the difference between nuclear sclerosis and cataract, using specialized equipment and their expertise. Also keep in mind that dogs can develop BOTH nuclear sclerosis AND cataract—many geriatric dogs do develop cataracts. If your geriatric dog has cloudy eyes but still appears to see well, this does not mean that they do not have cataracts—dogs can see fairly well if their cataracts are small. Dogs also can adapt well if one eye is blind from cataract and the other is not. Often, they adapt so well that the owner does not realize that the dog cannot see out of one eye. Dogs can also adapt well—up to a point—if both eyes gradually develop severe cataracts; dogs can develop a “memory map” as to where things are in their familiar environment. Dogs with poor vision do not let their owners know that they have a vision problem until it is severe in both eyes.
Cataracts have many causes in dogs, and sometimes it is not possible to identify the cause of cataracts in affected patients.
- Most cataracts in dogs are inherited and can occur at any age. The cataract may develop rapidly over weeks, or slowly over years, and occur in one or both eyes. Different breeds of dogs have different characteristics of cataract development. For example, cataracts in Bichon Frise dogs tend to develop rapidly in early adulthood and usually involve the entire lens in both eyes. Mixed-breed dogs can also develop inherited cataracts.
- The second-most common cause of cataracts in dogs is diabetes (diabetes mellitus). 75% of diabetic dogs will develop blinding cataracts within the first nine months of being diabetic. Often, the cataracts form very shortly after the dog becomes diabetic. See the accompanying article, Cataracts, Blindness, and Diabetic Dogs. Diabetic cataracts develop VERY fast—often overnight—in dogs, and they are a medical and surgical emergency. NOTE: Did you know that if a diabetic dog is supplemented daily with Ocu-GLO Rx™ BEFORE diabetic cataracts form, that this can help prevent blinding diabetic cataracts from forming?
- The third most common cause of cataracts in dogs is a toxic reaction in the lens—the lens is “sick”, due to some other ocular disease or (much less commonly) due to a drug reaction. These are called “toxic cataracts”. Toxic cataracts caused by ocular disease are quite common in dogs, and are caused by: 1) retinal degeneration, especially Progressive Retinal Atrophy (PRA)—see Progressive Retinal Atrophy (PRA) in Dogs; 2) uveitis (intraocular inflammation) of any cause, including trauma; and 3) secondary to glaucoma (increased intraocular pressure) of any cause—see Glaucoma.
- A special type of cataract occurs in dogs in which the lens capsule is ruptured due to trauma. The trauma can be penetrating (such as a cat claw injury or pellet gun injury) or a severe blow to the eye that results in lens capsular rupture. The lens contents leak out through the hole in the capsule and cause both cataract and a severe immune-mediated reactive uveitis; the uveitis does not usually “peak” in severity until 2–3 weeks AFTER the injury occurred. It is not always apparent that the lens capsule has ruptured; often, by the time this is diagnosed it is too late to save the eye and the eye needs to be removed. Thus, it is prudent to seek immediate medical attention for ANY injury to your dog’s eye. Lens capsules can also rupture if the lens swells, causing the capsule to stretch and split open. NOTE: This can also happen in diabetic dogs and in some types of inherited cataracts that rapidly form.
- Cataracts can also develop due to nutritional deficiencies in dogs, such as puppies on an artificial milk-replacer diet. These are called nutritional cataracts, and they often will improve as the puppy matures.
- Dogs also can develop cataracts with age (often after 8 years of life). However, age-related cataracts in dogs are usually small and do not significantly interfere with vision.
- There are many other potential causes of cataracts in dogs, such as birth defects, infection, radiation (usually from prolonged radiation therapy for cancer of the head), etc. but discussion of these causes is beyond the scope of this review article.
Once a lens has developed a cataract, there is no known method to make the lens clear again. Immature, mature, and hypermature cataracts can be treated by surgically removing them.
However, nutritional support of the lens can help to prevent or lessen the severity of developing cataracts. Nutritional supplementation can help to enhance lens health by providing oral antioxidants designed specifically for support of the canine eye. Antioxidant supplementation may also help reduce ocular inflammation that occurs in dogs both secondary to cataract formation and following cataract surgery. A unique antioxidant supplement product designed to support the health of the canine eye has recently been developed. Ocu-GLO Rx™ is a pharmaceutical-grade canine vision supplement containing 12 antioxidants; it is specifically formulated for support of the canine eye—especially for retina and lens health. Ocu-GLO Rx™ was developed by two veterinary ophthalmologists (one of which is Dr. Terri McCalla) and a compounding pharmacist.
It is important to understand that no cataract can be reversed; once the lens is cloudy, it stays that way unless cataract surgery is performed to remove it. Two exceptions to this rule are: 1) some nutritional cataracts can improve over time; and 2) hypermature cataracts can develop clear zones over time. However, as this process occurs in hypermature cataracts, damage to the eye also occurs in the form of lens-induced inflammation (called lens-induced uveitis or LIU). LIU, in turn, can cause glaucoma, retinal detachment, and/or lens luxation (slippage of the lens from its attachments, allowing the lens to float around inside the eye and cause damage and pain).
Cataract surgery is one of the most common surgeries performed on humans. However, not all dogs with cataracts need or should have cataract surgery. In fact, most dogs with cataracts do not need surgery, because most lens opacities in dogs (and a lens opacity is a cataract, no matter how tiny or big) are small and don’t significantly interfere with vision. Just because a dog’s eye has a cataract does not mean that the dog must undergo cataract surgery. Only a veterinary ophthalmologist can determine if cataract surgery is indicated in an affected patient.
Cataract surgery is a quality of life surgery—not a life-saving surgery. The ophthalmologist must evaluate many criteria before determining if a dog can or should undergo cataract surgery. However, it is also true (in Dr. McCalla’s view) that restoring a blind dog’s vision with cataract surgery is one of the most satisfying parts of being a veterinary ophthalmologist, and surgery can give a dog a wonderful new lease on life. For a blind dog to again be able to see its owner, to play with toys, look out the window and actually see things—this is life-changing for canine patients and their owners. This is especially true if the dog is elderly and deaf or hard of hearing, and/or has senile dementia and cognitive issues—to have its vision restored can make a huge difference in its quality of life.
The procedures and equipment used to remove cataracts in dogs are the same as those used in humans, and this equipment is highly technical and very expensive. The two most costly instruments used are an operating microscope and a phacoemulsification machine. A small incision is made in the eye and a hole is made in the capsular bag that holds the lens. Phacoemulsification is then performed, in which a special probe ultrasonically emulsifies and removes the cataract (all of the lens contents inside the capsule). After the cloudy lens is removed, the empty lens capsule remains and is called the capsular bag. An artificial replacement lens, called an intraocular lens or IOL, is placed in the bag. The eye is closed with extremely small absorbable sutures. IOLs are either rigid polymer plastic lenses or soft foldable lenses. The choice of which type of IOL to place inside an eye during surgery is determined by the ophthalmologist. Because even the slightest damage to structures in the canine eye can have disastrous effects, cataract surgery is extremely delicate surgery and is performed under general anesthesia with high-magnification using an operating microscope. If both eyes are affected, usually both eyes are operated on at the same time—especially in diabetic dogs. Back to Top
After successful cataract surgery dogs see close to normal. However, we cannot give dogs perfect vision. This is because an exact replacement of the original living lens is not possible. Furthermore, dogs have more inflammation in their eyes after surgery than humans and therefore have more scarring. This scarring does slightly decrease vision. The post-operative inflammation and scarring (lens capsular opacification) may be lessened by both anti-inflammatory drugs and oral antioxidant supplementation (Ocu-GLO Rx™). Capsular opacification is especially a concern in puppies and young adult dogs, and the best way to help reduce the risk of opacification is to implant an IOL, control uveitis, and provide daily supplementation with Ocu-GLO Rx™ . Some of the ingredients in Ocu-GLO Rx™ work synergistically to help reduce the risk of opacification. Once the capsule develops opacities, they cannot be medically reversed. In people, capsular opacities that develop following cataract surgery can be lessened with laser surgery, but this does not work in dogs. Most owners notice a tremendous increase in their pet’s vision after cataract surgery, but they can still detect certain visual difficulties.
After surgery, cataracts cannot recur. However, some dogs can have decreased vision years after cataract surgery due to formed scar tissue, glaucoma, and/or retinal detachment. In rare instances, placement of an IOL is not possible at the time of cataract surgery. These dogs still see better, but are more far-sighted and near objects are out of focus. The cornea does two thirds of the focusing of the eye, so vision is still present but not perfect if the lens (which does one-third of the focusing) cannot be replaced with an IOL. Some dogs require anti-inflammatory medication for several weeks, months, or lifetime following cataract surgery. Ocu-GLO Rx™ is a lifetime supplement following cataract surgery; this may help reduce the risk of capsular opacification, secondary glaucoma, and/or retinal detachment forming.
Cataract surgery is expensive because it requires specialized equipment and training. The instruments and equipment used for cataract surgery in dogs are the same type used for cataract surgery in people. Furthermore, you are paying for the highly advanced training and expertise of a board-certified veterinary ophthalmologist.
When people undergo cataract surgery, they usually pay very little for it because insurance picks up most of the tab of the surgeon’s fee, facility fee, and anesthesia/sedation fee. This is not the case in veterinary medicine. The pet owner pays 100% of the cost of cataract surgery and other health care for their pet. Even pet health insurance policies often exclude cataract surgery, because the cataracts are often genetic and most insurance companies will not cover genetic or pre-existing conditions. If you have health insurance for your dog, do not assume it will cover cataract surgery—check with your insurance provider.
Immature, mature, and hypermature cataracts can cause a serious reactive inflammation inside the eye (Lens Induced Uveitis, or LIU) that must be medically treated, whether or not surgery is performed. LIU can lead to complications such as glaucoma or a detached retina whether or not cataract surgery is performed, and LIU decreases the success rate of cataract surgery. An additional potential complication in eyes not undergoing surgery is lens luxation, which can be quite painful depending on how the lens slips (luxates) out of position. Glaucoma is also painful, in the form of a headache. Cataract surgery is an elective procedure. If surgery is not performed, lifetime anti-inflammatory eye drops and supplementation with Ocu-GLO Rx™ are required by Dr. McCalla, as well as periodic eye re-examinations. There is a best window of time in which to perform surgery. The earlier the cataract can be removed, the better. If you first decide to not have surgery performed but change your mind later, it is quite possible that surgery cannot be performed at a later date due to the decreasing surgical success rate over time.
If cataract surgery is not done, your dog might do just fine. However, it might not; the worst-case scenarios that could occur are that the dog eventually develops glaucoma secondary to LIU (which is chronically painful in the form of a headache), or develops extremely painful lens luxation. If these conditions cannot be controlled medically (and lens luxation usually cannot be medically controlled, especially if the lens luxates into the anterior chamber of the eye), then surgery is needed; either removal of the eye, or removal of the luxated lens if there is a hope of vision. There are other surgical choices for blind glaucomatous eyes (see Glaucoma).
It is also important to understand that most dogs that are blinded from cataracts can adequately adjust to their vision loss, if they are in a safe and stable environment and their eyes are not painful. You cannot determine if your dog’s eyes are painful from cataract development—if your dog has developed secondary glaucoma, it has a headache but will not show this in any obvious way, until it is too late. By that time, the affect eye is enlarged and completely blind due to destruction of the optic nerve. When this occurs, medication usually is not adequate to control the increased intraocular pressure, and surgery is needed to relieve the pain.
If your dog has cataracts but you believe that you cannot afford surgery, it is still VERY important for you to have your dog evaluated by a veterinary ophthalmologist! This is because medical treatment of the affected eye(s) is almost always needed to help prevent complications arising from the presence of the cataract. The cataract causes LIU, which in turn can cause many serious complications and the complete loss of the eye (including possible surgical removal of the affected eye).
Animal Eye Care LLC
Terri L McCalla, D.V.M, M.S, D.A.C.V.O.