What is a cataract?
The lens is a unique living ocular tissue that is usually clear or transparent and is referred to as 'the crystalline lens' in medical texts. The normal lens focuses light on the light-sensitive nervous tissue (retina) located in the back of the eye. The word cataract literally means "to break down." Doctors refer to any opacity (or cloudy change) of the lens that causes light to scatter as a cataract. Cataractous changes of the lens may appear as small insignificant pigmented, gray or white "dots"., microscopic "blisters", a "cracked glass" appearance, a diffuse haze, a "pearly" sheen, white streaks or a completely white lens. The cataract usually begins as small dots or microscopic blisters and progresses to involve larger areas of the lens. The rate of progression is difficult to predict and may be very slow or quite rapid. A cataract is different than the normal aging change that occurs in the lens which is called nuclear sclerosis. Nuclear sclerosis is in the very center of the lens and occurs in patients over 7 years of age. These are not cataracts! At times the cataract appears to worsen overnight. Cataracts may develop in one or in both eyes. If a large portion of the lens becomes white, it prevents images from reaching the retina and blurred vision results. When a light is shined into the eye of a patient with a complete cataract, the patient only sees a white light and no images can be seen.
This is a picture of a cat with cataractous lens. The cataract has liquified and the nucleus or center of the lens has sunk within the lens capsule. The arrow shows the nucleus.
What should I do if I suspect cataracts in my pet?
The first thing to do if your veterinarian indicates your pet may have a cataract of any size is to have your pet examined by a veterinary ophthalmologist. The lens is an important link of the total visual system, yet the health of the entire eye should be evaluated before the lens develops a complete cataract. Early evaluation of the eye with a cataract sometimes permits examination of the retina. If the cataract is complete or "mature," the retina cannot be directly examined and an ultrasound examination may be needed. At the time of the initial examination, the cataract may sometimes be identified as to cause, area of involvement and stage of progression. Not all cataracts lead to blindness. "Incomplete" cataracts may not impair vision significantly. If your pet has a cataract and has shown some visual loss, evaluation will include the consideration of and benefit of cataract surgery.
How do I know if my pet has a vision problem?
Our pets are creatures of habit and love to please their owners. If vision loss develops slowly over a long period of time, your pet may adjust to your home and yard. Pets in familiar surroundings may readily move about even when almost blind because they have learned where all objects are. Signs such as bumping into objects, failing to retrieve favorite toys and fear of being left alone may be signs of vision loss. These are especially significant if they occur within the pet¹s home or yard.
What causes cataracts?
The cause of cataracts is an area continually being studied. Cataracts may result from injuries to the eye, inflammation within the eye (uveitis), internal diseases that have an effect on the eye such as diabetes mellitus, metabolic conditions or certain foods, chemicals and drugs. Although it may be difficult to name the specific cause of a cataract, cataracts that develop in eyes free of signs of ocular disease are assumed to be inherited. Inheritance is the major cause of cataracts in dogs and cats.
Are there types of cataracts?
The type of cataract may not be important for deciding whether surgery may be performed. Cataracts may be classified by age of onset, physical appearance of the cataract or state of development of the cataract.
What is the treatment for cataracts?
There is no medical treatment known to slow the progression of, prevent the formation of or reverse the changes of cataracts. Surgery to remove the cataractous lens is the only known treatment in animals and man. Successful surgery can provide a return of vision.
Should my pet have cataract surgery?
Cataract surgery is generally restricted to those patients who are developing a cataract in both eyes. If one eye has a blinding cataract and the other eye has a rapidly developing cataract or if rapidly developing cataracts are present in both eyes, surgery is recommended so the patient will not completely lose vision. It is also important to consider whether the patient is a good candidate for anesthesia. With continued improvements in veterinary medicine and anesthesia, age alone does not limit the possibility of surgery. With the use of modern anesthetic agents, successful surgery is performed on dogs and cats 17-18 years of age and older. The over-all health of the patient needs to be assessed before surgery. This may include chest x-rays, EKGs, ultrasound of the eye, blood analysis or other procedures. Cataracts may be removed from one or both eyes during the same surgery. Finally, you are the one who hears all the information and decides if surgery will be performed to restore vision for your pet.
Is my pet a good candidate for cataract surgery?
Cataract surgery involves a period of intense treatment and care both before and after surgery followed by an extended period of low level therapy. If you are unable to provide this treatment, surgery is not recommended. Alternatively, if your pet will not or cannot be treated as required, he/she is not a good surgical candidate. Animals who "bite the hand that feeds it" don't do well after cataract surgery.
What will my pet see after surgery?
Patients benefit from cataract surgery because it will allow them to be able to move about without the fear of bumping into objects. As in people, the loss of the lens causes a loss of "up-close" visual acuity or sharpness. Without a lens, a pet may not have completely normal vision after surgery, but they do regain useful vision. The up-close image they see will be slightly larger and only partially focused so that the images will be much less distinct. Distant vision (over 6-to-8 feet) is usually normal. Our pets don't drive or play golf or tennis. Yet they need clear vision. Their need for sharp vision is not as necessary as it is for humans. Some veterinary patients appear visually handicapped without a lens yet most show no apparent vision difficulties. Due to the vision difficulties without lenses, we recommend replacement lenses be placed during surgery for the routine cataract surgery. These lenses are made to the same exacting specifications that are used in human medicine. The replacement lenses allow improved vision over a patient with no lenses.
What does cataract surgery involve?
The preparation for cataract surgery begins several days prior to the actual event. You will be required to apply drops to one or both eyes three times daily for three days. These drops are an antibiotic drop and a corticosteroid drop to reduce bacterial contamination and inflammation. An antibiotic will be given by mouth twice daily for three days before surgery. Cataract surgery is performed on an outpatient basis. The morning of surgery, the pressure of the eyes of your pet will be assessed and the area of fluid drainage will be examined to decide the type of postoperative medication that will be needed. If not previously performed, an ultrasound may be performed to examine structures inside the eye(s) that cannot be visually seen. Next, blood tests (if needed) will be performed, a physical examination given and a catheter is placed into a vein to facilitate the administration of drugs. Drops are placed in the eyes at specific intervals before surgery. General anesthetic is induced using the most modern agents. An electroretinogram [ERG] is then performed to determine that the retina is working normally and a reasonable chance for vision exists following surgery. This procedure is used if the cataract has progressed to the point that the ophthalmologist cannot assess the retina during the initial examination. If the ERG indicates that vision is not possible, then surgery is not performed and the patient is awakened. If the ERG shows that vision is possible, the patient is prepared for surgery and moved to the surgical center. During the surgical procedure, the pet's respiration, oxygenation level of the blood, heart rate and blood pressure will be monitored by the anesthetic technician. An EKG will be attached to your pet so that the heart can be assessed during surgery. Surgery is performed using an operating microscope and sophisticated microsurgical instruments. The actual surgical procedure may last 30-40 minutes and general anesthesia is normally for 60-120 minutes per eye. During recovery, your pet will be closely monitored and will be discharged from the hospital 2-6 hours after surgery. An Elizabethan collar (E-collar) is placed on the pet so they will not injure their own eyes during the first 7-to-14 days following surgery. Postoperative medications are used to reduce inflammation and to prevent infection. Eye drops are applied every 6 hours for the first 24 hours. Antibiotics and possibly other medications will be given by mouth twice daily. The first postoperative examination is scheduled for the afternoon the day following surgery. During that examination, the pressure within the eye will be examined, the eye is evaluated for inflammation, tear test will be performed and determination of possibility of infection will be made. Further examinations will be scheduled as needed to follow the progress of healing. Medication must be given at regular intervals. After the first two weeks, the chances of infection are very low and the antibiotics are discontinued. Inflammation is the main problem which must be overcome and controlled. Topically applied antiinflammatory agents, both steroidal and non-steroidal are given as frequently and as long as needed to control inflammation. It is possible, due to the fact that dogs and cats are great scar tissue formers, that treatment will be necessary for 6-to-12 months or longer. These treatments are usually once or twice daily and may be as infrequent as every other day. Some patients are completely off medication in 6 months. Each patient is an individual.
This patient was examined 24 hours following a successful surgery. The white arrow shows the artificial lens and the dark arrow shows the retinal blood vessels visible around the artificial lens.
Are there possible complications to cataract surgery?
The success rate in cataract surgery has improved markedly in the recent years with the advent of newer medications and microsurgical techniques. The success rate is 90-95%. This does not mean that if the surgery is not successful your pet will have 5-10% vision. It means that 90-to-95 pets out of 100 will have vision OR 5-to-10 pets will remain blind in spite of the surgery. Although the success rate has risen dramatically, there are still several complications that need to be anticipated in order to prevent them. Intraocular bleeding, elevation of intraocular pressures [glaucoma], extreme postoperative inflammatory response, adhesions and self-trauma are possible complications. The risk of anesthesia is extremely minimal. The chief problem which is treated on an on-going basis is inflammation (uveitis).
Have any questions on this subject? Contact
Dennis Hacker via E-mail:
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