Overview of Canine Cataracts
A cataract is any opacity in the lens of the eye. The dog’s normal lens is translucent (clear), and it transmits and focuses light onto the retina in the back of the eye. A cataract within the lens may block the transmission of light to the retina.
There are many causes of cataracts. The most common form of cataracts in the dog are genetic, inherited types. For genetic cataracts, the age of onset and severity varies among the various breeds of dogs.
Cataracts may also develop following trauma to the eye, in association with metabolic diseases such as diabetes, from nutritional disorders during puppy hood, or secondary to other eye diseases. Cataracts may develop spontaneously in old age, but should not be confused with nuclear or lenticular sclerosis, an aging change that often occurs in the canine lens and does not cause blindness. Rarely cataracts may develop following exposure to certain drugs, toxins, concentrated microwaves, radiation, or following electrocution.
Cataracts cause varying levels of vision impairment and may lead to blindness.
What to Watch For
Bluish, gray or white color change inside of the eye
Tendency to bump into things
Reluctance to use stairs or jump up onto objects
Hesitancy in unfamiliar environments
Other signs of blindness
Inflammation or redness
Pain and squinting due to the underlying cause
Diagnosis of Cataracts in Dogs
Diagnostic tests are necessary to recognize cataracts and exclude other diseases. Tests may include:
A complete medical history and physical examination.
A complete eye examination. Most veterinarians have the tools with which to confirm the presence of a cataract in the lens, but it is often necessary to visit a veterinary ophthalmologist to have a more thorough examination performed using an indirect ophthalmoscope and a slit lamp biomicroscope.
Blood tests to determine any underlying causes
An ultrasound examination of the eye if the cataract is too opaque to allow examination of the retina.
Possibly an electroretinogram to evaluate the function of the retina, especially if the cataract blocks visualization of the retina.
Treatment of Cataracts in Dogs
There is no medical treatment available to reverse cataracts, to prevent cataracts or to shrink cataracts.
Cataracts that are inherited or are not complicated by other eye diseases may be surgically removed. Cataracts associated with other eye diseases, such as inflammation (uveitis) cannot be removed surgically until the inflammation is brought under control.
Whether a dog is a candidate for cataract surgery can be determined by a veterinary ophthalmologist.
Treatment must also be instituted for any underlying causes, such as diabetes, etc.
Home Care and Prevention for Dogs with Cataracts
It is important to have all dogs with cataracts examined early in the course of their disease to determine whether the cataract is inherited or is secondary to other conditions. It is also important to determine whether the cataract itself is affecting the eye, such as causing inflammation or glaucoma. Early evaluation by a veterinary ophthalmologist allows appropriate therapy to be instituted for ancillary problems and allows a determination to be made as to whether the dog is a candidate for cataract surgery.
If your dog has inoperable cataracts, he may require help in adjusting to his blindness. Be sure to keep objects around the house in a consistent place. Confine the dog to a fenced yard or leash walking. Most blind pets function extremely well in familiar environments.
There is little you can do to prevent cataracts. If your pet is diagnosed with inherited cataracts, notify the breeder so that no other litters are produced from the same sire and dam.
If your dog is diagnosed with diabetes, then monitor blood and urine sugar as recommended by your veterinarian. Maintain good control of the diabetes.
Information In-depth for Dogs with Cataracts
Various eye diseases can cause a cloudy white appearance similar to that observed with cataracts. Many such diseases result in poor vision or blindness. Your veterinarian or veterinary ophthalmologist will be able to tell you if the white appearance and vision loss is caused by cataracts, by disease of the cornea (the clear outer covering of the eye), or the retina ( the specialized light receptor layer in the back of the eye).
Causes of Cataracts in Dogs
There are several causes of cataracts including:
Genetic. Cataracts in dogs are frequently inherited. Over 40 breeds of dogs are known to be predisposed to cataracts, including retrievers, spaniels, poodles, schnauzers, terriers, bichon frises, Siberian huskies and Old English sheepdogs. The Canine Eye Registration Foundation (CERF) maintains statistics on breeds of dogs and their reported eye diseases in order to make breeding recommendations (www.vmdb.org….click on CERF). In general, if a dog has cataracts and no other plausible cause can be determined, the cataracts are thought to be inherited.
For some breeds, there is a considerable experience regarding the natural history (progression) of disease. For example, in the golden retriever, cataracts are frequently centered in the back of the lens and tend not to progress. In the Boston terrier, cataracts may first be noted by 6 months of age and can rapidly progress causing blindness by age 2. In the bichon frise, cataracts may not be evident until the dog is 4 years old, and then the rate of progression is variable.
Trauma. If the lens is punctured or damaged from something like a cat scratch or a stick penetrating the eye, a cataract usually forms. Some of these form only at the site of injury, but others progress to involve the entire lens.
Diabetes. Diabetes mellitus (sugar diabetes) is a systemic disease in which regulation of blood sugar (glucose) is not controlled. The lens requires some glucose, but when the levels are too high, cataracts can form rapidly. Diabetic cataracts can develop even when an animal is receiving insulin.
Congenital, developmental cataract. Animals can be born with cataracts, but they are not necessarily inherited (genetic) cataracts. There may have been a problem in the development of the lens or of the blood vessel that surrounds the lens as it develops during the pregnancy.
Old Age. Age related cataracts are usually very small and tend to progress very slowly. A true senile cataract is not the same as the natural aging of the lens that gives it a bluish-white hue known as nuclear or lenticular sclerosis.
Secondary to other diseases. Retinal diseases such as progressive retinal atrophy and inflammatory eye diseases, such as anterior uveitis can cause cataracts. The underlying eye disease alters the nutrition of the lens, and a cataract forms. Nutritional deficiencies early in life, changes in blood calcium, exposure to certain drugs and toxins, exposure to concentrated microwaves, radiation therapy and electrocution may also alter both the nutrition and the structure of the lens, resulting in cataracts.
Veterinary care includes diagnostic tests and subsequent treatment recommendations.
Diagnosis In-depth of Cataracts in Dogs
Diagnostic tests are needed to recognize cataracts and exclude other diseases. These tests may include:
A complete eye examination. Most veterinarians have the tools with which to confirm the presence of a cataract in the lens, but it is often necessary to visit a veterinary ophthalmologist to have a more thorough examination performed using specialized ophthalmic equipment. Such an examination includes fluorescein staining of the cornea, Schirmer tear test, slit lamp biomicroscopy, tonometry, and possibly examination of the retina.
Cataracts are classified as incipient (very small), immature (encompassing more, but not all of the lens), mature (encompassing the entire lens) and hypermature (the lens is beginning to shrink down and slowly resorb). The eye exam is important for staging the cataracts and for detecting ancillary or underlying diseases.
Blood tests are necessary to search for diabetes and other underlying systemic diseases. Laboratory tests are also used to assess general health prior to cataract removal surgery.
An ocular ultrasound is performed if the retina cannot be examined because the cataract is too opaque, and if surgery is being considered. Prior to surgery it is important to determine if the retina is normal or healthy. If a retinal detachment or changes in the vitreous (jelly-like substance behind the lens) are found, then surgery to remove the cataract may not be worthwhile.
An electroretinogram (ERG) is also frequently performed prior to cataract surgery in order to evaluate the function of the retina. An ERG is especially important in determining underlying retinal disease masked by the cataracts (if the lens is too opaque for all the retina to be examined). If the ERG is abnormal, then the cat is not a good candidate for cataract surgery.
To understand the importance of evaluating the rest of the eye and especially the retina prior to surgery, consider this analogy: A cataract is like a physical barrier to light, similar to a cover over the lens of a camera. This barrier can be physically removed by surgery. In contrast, the retina is like the film in the camera, and the rest of the eye is the camera itself. If the camera or the retina is not working properly, then removing the lens cover (cataract) will not improve the animal’s vision. The rest of the camera must be working well and the film must be good before removing the barrier over the lens will be worthwhile.
Treatment In-depth for Dogs with Cataracts
Treatments for cataracts may include one or more of the following:
Cataract Surgery for Dogs
Cataract surgery. At the present time, there is no laser surgery for removing cataracts in either people or animals. Phacoemulsification is the most common technique used in both humans and animals to remove a cataract. Once the pupils have been dilated and your pet is under general anesthesia, a small incision is made through the cornea (clear domed front surface of the eye). The lens is housed in a small bag called the lens capsule. A small tear is made in the front capsule and a circular piece of the capsule is removed. The phacoemulsification instrument uses ultrasonic waves to break apart the lens and then suck it out. Most of the lens is removed by phacoemulsification, and then the lens capsule (the “bag”) is cleaned of any remaining lens material. Frequently an intraocular lens implant (a prosthetic lens) is then placed into the lens capsule.
The lens capsule acts as a bag to hold the implant in place. There are lens implants for both dogs and cats, and these prosthetic lenses return the vision as close to normal as possible. There are some situations where a lens cannot be inserted. When no lens implant is used, an animal’s vision is still greatly improved by cataract surgery.
The incision through the cornea is then stitched closed after the lens has been removed.
Extracapsular lens extraction. This is another cataract removal technique. It is used either when a phacoemulsification machine is not available, or when a cataract is so hard or old that the phacoemulsification instrument isn’t powerful enough to break up and remove the lens. The surgical procedure requires making a larger incision through the cornea and a larger hole in the lens capsule so that the lens can be removed from the bag as a whole. A lens implant can still frequently be inserted during this type of procedure.
Intracapsular lens extraction. This is another surgical method that involves making a large incision through the cornea and removing the whole lens in its capsule. This procedure is generally used when a cataractous lens has shifted out of position and is no longer held firmly in place inside of the eye. Because the lens capsule has been removed, if a lens implant is going to be used, it has to be sewn into place because there is no capsular bag left to hold it in the center of the eye.
Regardless of which type of procedure is used to remove a cataractous lens, there are many postoperative medications and important home care instructions to be followed after surgery.
Cataract surgery has a high success rate, as long as the rest of the eye is healthy. The success rate of cataract surgery is decreased if the eye has been inflamed in the past, or is actively inflamed. All uveitis must be controlled before cataract surgery can be attempted, and other eye problems such as retinal disease and glaucoma must also be ruled out.
Risks involved with cataract surgery include those associated with general anesthesia. Anesthetic risks are minimized by evaluating pre-operative laboratory tests, performing a complete physical exam, and taking x-rays of the chest. The information gathered from these tests is then used to develop an appropriate anesthetic protocol.
Anterior uveitis and glaucoma are the two most immediate and common complications encountered in the days following cataract surgery. Many dogs are medicated prior to surgery to combat the uveitis that occurs once the eye is opened, and these medications are continued for weeks following the surgery. Pressure within the eye is monitored closely following surgery, and anti-glaucoma drugs are started as needed.
The most common problems that arise long-term after cataract surgery are scarring of the lens capsule that remains in the eye and detachment of the retina. Because of both short-term and long-term problems that may be encountered after cataract surgery, frequent follow-up visits are needed for sometime.
If your pet’s cataracts are secondary to some other eye disease, removal of the cataract is frequently contraindicated.
Medical therapy may be necessary to control inflammation within the eye, to combat any glaucoma present, and to treat underlying illnesses, even when the cataract cannot be removed. Periodic follow-up examinations are required to keep the eye healthy and the cat comfortable.
After cataract surgery, the first one to two weeks are the most labor-intensive. The dog must be kept quiet and calm. Usually an Elizabethan collar is used to keep the dog from rubbing or traumatizing the eye. This collar should stay on at all times. Playing, barking and jumping should be discouraged and all pressure around the head should be minimized. Use of a harness rather than a collar is recommended for two to three weeks after surgery.
Follow-up Care for Dogs with Cataracts
Follow all instructions your veterinarian gives you for medications. Several topical (drops) and oral medications may be used after surgery, such as: anti-inflammatory drops (prednisone/prednisolone, dexamethasone, flurbiprofen, diclofenac); dilating drops (tropicamide, atropine); antibiotic ophthalmic drops; oral anti-inflammatory drugs (prednisone, carprofen); and oral antibiotics (amoxicillin, cephalexin).