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About Animal Vision  
C O N T E N T S
ANIMAL VISION (1)

  • Eye Anatomy Glossary

  • Vision in Animals

  • Eye Problems in Animals

    - Glaucoma

    - Uveitis and Golden Retriever Uveitis- FAQ

    - Keratoconjunctivitis Sicca (KCS)

    - Corneal Ulceration

    - Progressive Retinal Atrophy (PRA)

    - Cataracts

    - Nuclear Sclerosis
  • ANIMAL VISION (2)

  • Eye Problems in
        Exotic Animals


  • Caring for Your
        Blind Pet


  • Links about Blind Pets



  •  EYE ANATOMY GLOSSARY

    Click the name
    of the part of the eye
    in diagram for a definition


    Cornea: The clear front part of the eye that covers the iris, pupil and anterior chamber. It is covered with a transparent epithelium.

    Corneal Ulcer: An erosion or scrape on the cornea in which some of the epithelium is lost.

    Iris: Colored part of the eye. Brown irises have pigment. Blue irises have much less pigment. The iris controls the amount of light that enters the eye, by varying the size of the pupil opening.

    Aqueous humor: clear fluid inside the eye, which provides nutrition for the lens and cornea.

    Iridocorneal Angle or Drainage Angle: The eye contains a clear fluid called aqueous humor. The aqueous humor is produced in the ciliary body and drains, via the angle, out of the eye into the bloodstream.

    Glaucoma: Elevated intraocular pressure that usually causes vision loss. Glaucoma occurs when the drainage angle is blocked with inflammatory debris, or if the drainage angle is abnormally formed from birth, or of the normal flow of fluid inside the eye is blocked in some other way (by a tumor for example).

    Pupil: The hole in the iris. The pupil gets smaller in bright light, larger in dim light conditions.

    Uvea: The vascular tissues of the eye. This includes the iris, ciliary body and choroid.

    Uveitis: Inflammation of the uvea, can be anterior or posterior.

    Lens: Clear and as thick as a stack of 5 dimes. It is suspended behind the iris by hundreds of microscopic fibers. The lens is biconvex (ie it is shaped like a lentil bean). The lens helps to bring rays of light to a focus on the retina.

    Cataract: An opacification (cloudiness) of the normally clear lens.

    Inflammation: Irritation, redness, swelling of any tissue. Inflamed eyes may appear red. A pet may rub or scratch their eye when inflammation is present. If painful, animals may also squint.

    Lens capsule: A cellophane-like covering of the lens (only much thinner!). During cataract surgery the anterior lens capsule is partially opened so that the abnormal lens material can be removed.

    Nictitating Membrane (Third Eyelid): Nictitating Membrane is a thin piece of tissue, supported by cartilage, which moves across the eyeball like a windshield wiper, to give the cornea additional protection. It is often called a third eyelid or haw. In cats and dogs, the nictitating membrane is not usually visible, and its appearance is a sign of poor health or a painful eye.

    Vitreous humor: Clear gel behind the lens which fills the rear 2/3 of the eyeball (aqueous humor fills the anterior 1/3) and helps keep the retina attached.

    Retina: A thin layer of light sensitive nerve tissue in the back of the eye that allows us to see, by conversion of optical images to electrical impulses that are sent by the optic nerve to the brain.

    Tapetum: The tapetum is a reflective structure that lies beneath the retina. It acts like a mirror; reflecting light back through the retina so the retina gets two chances to catch the light. Animals that are active at night have a tapetum. Dogs, Cats, Horses, and Cows all have tapetums. It causes the yellow or green glow you see when light hits an animal's eyes. Humans do not have a tapetum.
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     VISION IN ANIMALS

    Color Vision
    There are two types of cells in the retina that receive light: rods and cones. Rods are for sensing motion and work best in low light conditions. All mammals, including people, have more rods than cones. Cone cells are adapted for vision in brighter light and can detect different colors. Humans have three types of cones. Dogs have two types of cones. Evidence suggests that the dog has vision similar to a human who is red-green colorblind. Cats have three types of cones, like people, but do not have exactly the same color vision as we do. Cats live in a world of fuzzy pastels.

    Dogs and cats appear to respond to blue and yellow best, and seem to have more trouble with green and red. What appears red to us is simply dark to the dog and cat, and green light is almost indistinguishable from white (a shade of gray). Colors that would appear very rich to us are more pastel-like to the cat. The cat sees a green, grassy lawn as a whitish lawn, and a green rosebush as a whitish bush with dark flowers.


    Visual Acuity
    Visual acuity is the ability to see the details of an object separately and unblurred. Acuity is measured in "cycles per degree", which means how many lines you can distinguish as being separate in a degree of the visual field. Humans see 30 cycles per degree, horses 18, dogs 12 and cats 6. Acuity in dogs is 0.4 times that of people, 0.67 times that of horses, and twice that of cats. Acuity in cats is 0.2 times that of people, 0.33 times that of horses, and 0.5 times that of dogs. If normal human vision is 20/20, then that of the dog between 20/50 to 20/100, the horse 20/33, and that of the cat is 20/100. However, it is difficult to measure acuity in animals so studies have often shown wide variations in results.



    The picture demonstrates the idea of acuity and how it differs between humans (top) and dogs (bottom). Humans can distinguish a lot more "cycles" in the same picture. To a dog, the upper image would be a gray blur with no alternating lines.


    Sensitivity to Light
    The canine and feline visual systems are adapted for performance under low light conditions. These animals have large corneas and pupils to collect more light in dim light conditions. They also have a reflective structure at the back of the eye called the tapetum which reflects light back out of the eye. This way, the retina gets two chances to capture each photon of light. A cat's tapetum reflects 130 times more light than the human eye. This is why we see the shiny dog and cat eyes in photographs and at night when headlights or other types of light enter the eyes. Cats can detect light that is 6 times dimmer than that which normal humans can detect. Dogs also detect much lower levels of light than humans (but not as low as cats).

    Dogs and cats are also very sensitive to motion, especially when compared to an object that is not moving. Some dogs were shown to recognize a moving object at 800-900 meters. If the same object was stationary they only recognized it at 500 meters. People are also more sensitive to motion than to objects that are standing still.


    Fields of View
    Dogs and cats can see about 150° around from their nose. The horse can see about 350° around because their eyes are positioned to the side of the head. This makes horses better able to watch for potential predators. Humans have a smaller field because our eyes are directed straight ahead. Binocular vision (stereo vision) occurs where the visual field of the two eyes overlaps. In the binocular field depth perception is improved and vision is better. Dogs and cats have some binocular vision but not as much as people. In dogs and cats the binocular field is 85°, in horses it is around 65°, and in people it is around 120°.
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     EYE PROBLEMS IN ANIMALS

    GLAUCOMA

    Definition:
    Glaucoma is defined as excessive pressure inside the eye. The eye is full of a fluid called the aqueous humor, which is constantly produced and drained away from the eye and supplies nutrition for all interior structures. Glaucoma is caused by a decrease in the amount of fluid that flows out of the eye. It is a serious disease and without proper treatment can result in blindness. Unfortunately, even with aggressive medical and surgical therapy, dogs and cats with glaucoma will often lose their vision. Glaucoma is one of the most frequent causes of blindness in adult dogs.

    Types of Glaucoma:
    There are two main types of glaucoma, primary and secondary. In primary glaucoma, the cause of the increase in pressure is due to decreased outflow from the drainage angle. It is frequently an inherited problem. Beagles, Basset Hounds, and Cocker Spaniels are especially prone to this type of glaucoma. In secondary glaucoma the pressure is too high because something else is wrong in the eye, such as a lens luxation, bleeding, inflammation, or tumor.



    Aqueous humor made in the ciliary body flows through the pupil into the anterior chamber. Aqueous then drains into the bloodstream through the iridocorneal angle.

    Signs of Glaucoma:
    1. A red (bloodshot) eye
    2. A painful eye
    3. Lids may be held shut
    4. Excessive tearing
    5. Eye may appear cloudy or blue
    6. Sudden blindness
    7. A dilated (enlarged) pupil that does not respond normally to light
    8. Depression
    9. Appetite loss
    10. Enlargement of the eye

    Treatment:
    The treatment chosen (i.e. surgery and/or medical therapy) will be influenced by what the goal of therapy is: to stop pain in a blind eye or to preserve vision. Medical treatment consists of a number of different drugs used in combination. Some are given by mouth and effect the whole body, while others are put directly into the eye and have a local effect. The drugs that work when the problem is first diagnosed may not work forever. Therefore, the intraocular pressure needs to be monitored on a regular basis so that the medication regimen can be altered to fit the needs of the patient. Unfortunately glaucoma cannot be cured, only controlled. When medical treatment fails, surgical therapy can help prolong vision, or eliminate pain.

    Medical Therapy:
    The following categories of drugs are frequently used:

    Carbonic anhydrase inhibitors: Oral and topical formulations reduce the amount of fluid produced inside the eye. (Methazolamide, dorzolamide or Trusopt )

    Miotics (Parasympathomimetics): Used on the eye, they help to increase the outflow of fluid from the eye. They may cause a temporary redness, burning or stinging in the eye. (Pilocarpine)

    Beta-adrenergic blockers: reduces the amount of fluid produced inside the eye. (Timolol)

    *By using very small amounts of several of the drugs, the risks of side effects can be reduced.

    *Please keep these drugs out of the reach of children.

    Surgical Treatment:
    In some cases, surgical procedures are available that may help to provide long-term control. One of these procedures uses a laser to destroy the part of the eye that produces fluid and thereby reduces the pressure. Another surgery inserts a tube into the eye that shunts the fluid under the conjunctiva (pink tissue) deep in the eye socket. Neither surgery is 100% effective and multiple surgeries over several years may be required to preserve vision.

    A blind, painful eye can be removed to eliminate discomfort for your pet and to avoid the need for medicines that are expensive and affect the whole body. The surgery to remove the eye is called enucleation. After the eye is removed, the eyelids are permanently sewn shut. This means that the dog will look like he or she is winking at you.



    Blind painful eyes may also have an intraocular prosthesis placed after a procedure called evisceration. With this surgery the contents of the eye are removed and silicone prosthesis is placed inside the eye. The outward appearance of the eye is preserved but no longer has the pain from high pressure. Afterwards, the eye looks fairly normal, but remains blind.

    EVISCERATION WITH PLACEMENT OF AN INTRASCLERAL PROSTHESIS: This surgical procedure is a cosmetic alternative to enucleation and is performed on blind and painful eyes. The contents of the eye are removed and a sterile silicone ball (the prosthesis) is placed within the eye. The looks fairly normal, moves normally, remains blind, but is no longer a source of pain. The photographs below show a dog with prostheses in both eyes (the smaller photo is a closer view.



    Remember:
    Each case is different and therapy must be tailored to the individual patient. Intraocular pressure must be measured regularly and the eye should be treated as prescribed. Do not stop any medication unless directed to do so by your veterinarian.


    UVEITIS AND GOLDEN RETRIEVER UVEITIS - FAQ

    What is uveitis?
    Uveitis is defined as an inflammation of the parts of the eye (the uvea), which contain blood vessels, i.e. those parts of the eye that are connected by blood vessels to the rest of the body. The uvea consists of three parts, the iris, the ciliary body and the choroid. (See diagram.) When the blood vessels in these structures become leaky, then cells and proteins and fats inside the blood stream can get from the blood to the inside of the eye. Basically, uveitis is inflammation or infection inside the eye rather than on the external surface of the eye.

    What are the signs of uveitis?
    Signs of uveitis include cloudiness, redness, pain, a small pupil and sometimes, decreased vision.

    How do I know if my pet's eye is painful?
    Dogs, cats and rabbits usually exhibit one or more of the following signs if an eye is painful: Squinting, tearing, rubbing at the eye with a paw, rubbing at the eye on furniture or the rug, holding the eye shut, redness, decreased appetite, depression, and/or an elevated third eyelid.

    What causes uveitis?
    There are many causes of uveitis. Diseases such as those caused by viruses, bacteria, parasites or fungus can cause inflammation inside the eye. Other causes include trauma to the eye, cataracts, cancer (either in the eye or in the body), and autoimmune disease. Some specific diseases that can cause uveitis include the following:

    Bacterial: Brucellosis, Leptospirosis
    Rickettsial: Rocky Mountain Spotted Fever, Lyme Disease, Erlichiosis
    Parasitic: Toxoplasmosis, Protothecosis
    Fungal: Blastomycosis, Cryptococcus, Coccidiomycosis, Aspergillosis, Histoplasmosis
    Immune mediated: Vogt-Koyanagi-Harada Syndrome, Lupus
    Neoplasitc (Cancer): Lymphosarcoma, multiple myeloma, melanoma, tumors that either originate in the eye or spread to the eye from somewhere else in the body

    How can you tell what the cause of uveitis is?
    In many (if not most) cases we might not identify an exact cause. However, we can still treat the symptoms with anti-inflammatory medication, without knowing the exact cause. But because it would be better if we could know the etiology, we usually perform medical tests as follows:

    1) General blood screening: a CBC and chemistry panel
    2) Chest X-ray- to look for tumors or pneumonia
    3) Abdominal ultrasound - to look for problems in kidneys, liver, spleen and other organs
    4) Testing for specific diseases as dictated by where the pet lives (what part of the U.S., indoor or outdoor) and travel
    history, i.e. for Blastomycosis in Wisconsin, Rocky Mountain spotted fever, Lyme disease, Toxoplasmosis
    5) Ocular ultrasound is sometimes helpful
    6) Aspirate of the fluids inside the eye

    Is uveitis curable? Sometimes it is. We treat with medications for a few weeks and in many cases the inflammation resolves. If severe, however, it can cause scarring inside the eye that does not go away. This scarring can cause problems later on, such as glaucoma (high pressure inside the eye), cataracts, or blindness.

    For some conditions, like certain autoimmune conditions or in Golden Retriever Uveitis Syndrome, it does not go away. It may wax and wane and be somewhat controllable on medication, but the animal will need to stay on treatment life-long. In other situations, the uveitis will not resolve until the underlying condition is under control or cured, such as with systemic diseases like uterine infection (pyometra), dental disease, or cancer.

    What is Golden Retriever Uveitis?
    Golden Retriever Uveitis is syndrome of Golden Retriever Dogs characterized by progressive inflammatory changes in the eye related to pigment deposition (especially on the lens) as well as cyst formation inside the eye. These changes tend to get worse over time and can lead to permanent scarring. GRU may be mild and easy to control but many eyes eventually develop glaucoma, pain, and blindness. If an eye is blind and painful the best option to maintain quality of life is to remove the eye. In one study almost 50% of Golden Retrievers with uveitis developed painful glaucoma.

    What are the first signs of uveitis?
    Early signs of the condition include the formation of non-painful iris or ciliary body cysts (see below) or an increase in the iris pigment in one or both eyes. These changes may not be observed on casual observation by the owner, or even on a quick eye exam by a veterinarian.

    Can my family veterinarian diagnose Golden Retriever Uveitis?
    Accurate diagnosis of GRU usually requires specialized training and equipment. A complete ophthalmic examination to identify this condition would require slit-lamp biomicroscopy, indirect ophthalmoscopy, applanation Tonometry and possibly gonioscopy. Veterinarians who specialize in ophthalmology will have this equipment and expertise that is usually not available to the general veterinarian. (
    http://www.acvo.com/)

    What are iris or iridocilliary cysts?
    Iris cysts are small fluid-filled structures either attached to the iris or to the ciliary body (the tissue that is behind the iris) or floating free inside the eye. They occur most commonly in dogs, especially Golden Retrievers, Boston Terriers and Labrador Retrievers. In most cases, they cause no problem. But when there are large numbers of them they can obstruct the drainage angle of the eye and cause glaucoma. When they pop they can leave a heap of pigmented tissue in the visual field. They can be deflated with a laser beam or aspirated out of the eye with a tiny needle. General anesthesia is usually needed for these procedures. The cysts should be differentiated from iris melanomas, by shining light through them (transillumination). They are occasionally seen in cats and horses.

    What age dogs are affected by Golden Retriever Uveitis?
    In a recent study of 66 dogs with this condition, the mean age of affected dogs was 8.6 years, with a range between 4.5 and 14.5 years.

    Are both eyes affected?
    Most dogs were affected in both eyes.

    What were other characteristics of the disease in the study?
    37% of dogs developed cataracts.
    46% of dogs developed glaucoma.

    What is the prognosis of GRU?
    In the study mentioned above, 46% of dogs eventually became blind due to glaucoma.
    In general the prognosis is poor for vision and poor for maintenance of a comfortable blind eye.

    How do dogs get Golden Retriever Uveitis?
    It is considered to be an inherited condition. Dogs with this condition should not be bred.

    Is there any way to prevent my Golden Retriever from getting uveitis?
    No, there are no drops, pills, supplements, diets or exercises that will prevent your dog from getting Golden Retriever Uveitis if he is predisposed by genetics to get it. But the condition can be treated with medications once it is identified.

    How is Golden Retriever Uveitis treated?
    A combination of topical and systemic anti-inflammatory drugs are used; both steroidal and non-steroidal medications. These may include one or more of the following: dexamethasone, prednisolone acetate, flurbiprofen, carprofen, prednisone, meloxicam, and aspirin. Sometimes drugs are used to dilate the pupil (such as atropine) but these must be used with caution, especially in eyes that are predisposed to glaucoma.

    Once the eyes become glaucomatous, then glaucoma medications are added to the treatment list. These might include drugs like TimololŪ, AzoptŪ, methazolamide and many others to lower the pressure inside the eye.

    What happens if my dog becomes blind?
    Dogs can do very well, even if totally blind. They navigate their familiar environments with ease and usually learn to deal with stairs, swimming pools and other obstacles. Outside the home there is more need for monitoring; they should never be left near cars without a leash. Dogs, cats and rabbits can live happy lives even if totally blind, provided the eyes are no longer painful and they live in a loving and supportive environment.

    How do you relive the pain in a blind eye that has glaucoma?
    Once the eye is blind, the easiest way to relive pain is complete removal of the eye. While at first that might sound harsh, remember that the dog or cat is not concerned with appearance, they only want to be without discomfort. Removing the eye (enucleation) completely relives this pain. There is nothing red or gaping after removal of the eye. The wound is sewn shut and it simply appears that the animal is holding one eye shut. Another option is evisceration. With this later surgery, the contents of the eye are removed, leaving the cornea and sclera in place. The contents of the eye are replaced with a silicone prosthesis. These eyes are cosmetically pleasing as they move normally and the eyelids blink, but they don't look exactly like a normal eye. Usually some cloudiness is present due to scarring of the cornea. The surface of the eye remains vulnerable to scratches, infection and dry eye.

    References: Sapienza JS, Simo FJ, Prades-Sapienza A. Golden Retriver uveitis: 75 cases (1994-1999). Vet Ophthalmology 2000;3(4):241-246.


    KERATOCONJUNCTIVITIS SICCA (DRY EYE)

    What is KCS?
    Keratoconjunctivitis sicca (KCS) is also called dry eye. This condition is due to a deficiency in tear production and results in a red, itchy eye with a thick mucous discharge. The tear production is measured by the Schirmer Tear Test. In this test a standardized paper strip is gently placed on the eye and allowed to absorb tears for one minute. Wetting values of less than 15 mm per minute are abnormal.

    DRY EYE: Below are two dogs with dry eye.



    The cornea is the front window of the eye. In the normal eye it is kept clear, moist, and smooth, by the tear film. In the condition of dry eye, the cornea is vulnerable to exposure, dry air, and bacteria. In order to protect itself, scar tissue starts to cover the normally clear cornea. This tissue consists of blood vessels, and pigment and results in a thickening of the cornea so that it appears dull and cloudy (photo on the left below). Tears are made of mucus, water and oils. Dry eye is a deficiency of the watery (or aqueous) part of the tears. Therefore, animals with KCS, accumulate a lot of mucus (photo on the right).

    Why does this happen?
    Acute KCS results in a very red and painful eye with a lot of discharge. The condition may be associated with viral diseases, trauma, drug toxicity (some types of antibiotics and some types of non-steroidal anti-inflammatory medications for example), allergy, or general anesthesia.

    Chronic KCS results in intermittent redness with a profuse, ropy, thick discharge that adheres to the eye. Without treatment, the cornea may eventually pigment and scar to result in loss of vision. This can be familial in certain breeds, associated with immune-mediated diseases, secondary to chronic inflammation of the eye, or idiopathic (no known cause).

    How long will this problem last?
    Sometimes the condition resolves and spontaneous tear production resumes. The acute form is more likely to resolve. Chronic KCS may or may not resolve, and those animals with lower tear values (near zero) are harder to control. Medical therapy may need to be given for the lifetime of the animal. If medical therapy fails, surgery to transplant a salivary gland duct into the eye can sometimes help control the problem.

    The importance of reexamination:
    The tear test should be repeated to monitor progress and improvement in tear production. Premature discontinuation of the treatment can allow the condition to worsen. Due to corneal pigmentation and scarring, the condition can cause blindness if left untreated.

    How is this treated?
    Animals with acute dry eye frequently have corneal ulcers and they must be treated aggressively with antibiotics and tear replacement to avoid perforation and loss of the eye. Both acute and chronic KCS are treated by topical tear substitutes as well as stimulation of existing tear production. Cyclosporine ointment (Optimmune , Schering Plough) is used to increase tear production and reduce inflammation. Sometimes cyclosporine used 2x/day can control the KCS effectively without additional medications.

    In some cases, topical antibiotics and/or corticosteroids are used in the treatment of KCS. The tear film has natural antibacterial action that must be replaced by antibiotic therapy. Anti-inflammatory drugs are frequently used to help control scarring and irritation.

    It is important to clean accumulated mucus from eyes or lids with eye wash and cotton balls prior to instilling medications.

    Be sure to keep all medications out of the reach of children.

    Follow the medication schedule that you have been given. Premature discontinuation of medication is the most common cause of treatment failure.

    Important Note:
    If your pet is on a topical steroid (hydrocortisone, dexamethasone, or prednisolone), always call your veterinarian if your pet exhibits signs of pain (squinting, or rubbing at the eye). If a corneal ulcer develops, topical steroids must be discontinued immediately. When in doubt, stop topical steroids until your veterinarian checks the eye.


    CORNEAL ULCERATION

    The cornea is the front clear part of the eye and is covered with a clear epithelium (skin layer). The corneal epithelium is like our skin except that it is clear and smoother. If the corneal epithelium is scratched, scraped or rubbed off, the resulting defect is called a corneal ulcer. This condition is painful and animals with ulcers often squint and rub at their eyes.



    A corneal ulcer can be a sight-threatening emergency if it deepens or becomes infected. This can happen rapidly (overnight), so prompt attention to a painful eye is essential.


    PROGRESSIVE RETINAL ATROPHY (PRA)

    General Information
    Progressive retinal atrophy (PRA) is a name given to a group of eye diseases of similar character. PRA causes no pain or discomfort but may result in permanent blindness. The word atrophy means wasting away.

    PRA develops after birth and in some breeds has been determined to be inherited from both parents. It affects the retina, which lines the back portion of the inside of the eye. The retina contains the light-sensitive rods and cones that change light into energy for transmitting messages to the brain. The retina is similar to the film in a camera; the image or picture is received on it.

    PRA can occur in all breeds of dogs and cats although certain breeds are at higher risk. It appears earlier in some breeds and can take several years to cause complete blindness. An early sign of PRA is inability to see in dim light or at night. For example, an animal with PRA may hesitate to go from a well-lighted room into a darkened room.

    Due to PRA's slow progress, most pets adapt very well to the gradual loss of sight. Many owners do not realize their pet is becoming blind. Animals compensate well for blindness, because their senses are much more acute than those of people.

    Important Points about PRA:
    1. No effective treatment is available.

    2. Complete blindness eventually results.

    3. The condition, however, is not painful.

    4. PRA is prevented through selective breeding of animals with normal eyes.

    5. Sometimes cataracts develop secondary to the retinal degeneration. But because of the retinal degeneration, cataract removal would not help the animal regain vision.

    6. Poor vision in dim light is the first sign you will see in your dog.

    7. You may also eventually see dilated pupils.

    Notify the Doctor if Any of the Following Occur

    · You notice a sudden change in your pet's vision or in the appearance of the eyes.

    · Your pet shows pain or discomfort.


    CATARACTS

    A cataract is opacity of the lens of the eye. The lens is behind the iris (the brown or blue part of the eye) and can change its shape allowing animals to see close objects. A thin capsule (the consistency of cellophane) covers the lens.



    In front of the lens is a clear fluid, called aqueous humor, and behind the lens is a clear gel, called the vitreous humor. The vitreous helps keep the retina attached. The retina is a layer of cells that functions in a manner similar to the film in a camera; it receives light and allows animals to see.

  • ACVO Cataract Video

    Causes of Cataracts
    Cataracts may develop because of an inherited defect, with age, or secondary to inflammation, trauma, diabetes, or retinal degeneration.

    Cataract Progression
    As cataracts progress, they go through different stages: immature, mature and hypermature. In the later stage cataracts may leak proteins into the eye. These proteins can incite inflammation. The term for inflammation inside the eye is uveitis. Lens-induced uveitis is inflammation inside the eye caused by a leaky lens. The eye has an allergic-like reaction to this lens material. Lens-induced uveitis can damage the eye leading to complications such as glaucoma, retinal degeneration or retinal detachment, all of which can result in blindness.

    Cataract Surgery
    In cataract surgery the lens (cataract) is removed along with the front part of the lens capsule. The capsule covering the back of the lens is usually left in place to maintain the normal arrangement of the structures in the eye. In some cases an intraocular lens implant may be inserted to improve close-up vision after surgery.

    To perform cataract surgery the patient must be under general anesthesia. Then, an incision is made in the cornea and the lens is removed. Two types of surgery are used in animals. In most cases a small incision is made and phacofragmentation performed. Phacofragmentation (also called phacoemulsification) utilizes hi-frequency sound waves to break up the lens and then the small fragments are removed.

    The second type of surgery is performed in cases where the lens is too hard to be broken up by the phacofragmenter. Very old animals may need this type of surgery. A larger corneal incision is made and after removal of the capsule, the lens is gently expressed from the eye in one piece.

    Patient Selection and Preparation
    In order for your pet to be considered for cataract surgery, he or she must be relatively free of serious illnesses, skin disease and dental disease. Pre-operative blood tests are performed in all animals to help rule out any undetected kidney or liver problems.

    In order for your pet to benefit from surgery, the retina, the tissue in the back of the eye that receives light, must be intact and functioning. Ocular ultrasound is performed before surgery to make sure the retina is attached. An electronic retina test called an electroretinogram (ERG), is also performed to make sure the retina is functioning well enough to go ahead with surgery.

    Owner Participation
    After cataract surgery, you will have a lot of work to do to help achieve a successful outcome. Several types of eye drops need to be given 4 times a day for at least a few weeks after surgery. Also, oral medications are given for a few weeks after surgery. Eventually these medications are decreased, discontinued or used in very small amounts. Sometimes, however, an animal may need some medication for extended periods of time.

    An Elizabethan Collar is necessary for two weeks to keep your pet from rubbing its eyes after surgery.

    Several recheck visits are required after surgery. Typically there are 2-3 visits during the first two weeks following surgery and then every few weeks- months for the first 6 months. Then we may recommend rechecks 1-2 times per year. These rechecks are necessary to detect and avoid any complications of surgery that may decrease vision.


    NUCLEAR SCLEROSIS

    Nuclear Sclerosis is a normal aging change of the lens. The lens is made up of several layers of cells arranged somewhat like the layers of an onion. Layers of cells are added continually throughout the animal's life. As your dog or cat gets older, new layers are added and the cells become packed together more tightly in the center of the lens (the nucleus). The increased density of the lens causes it to look more cloudy in dogs over seven years of age. The lens will become increasingly cloudy as the animal ages, but it almost never has an effect on vision.

    Nuclear Sclerosis should not be confused with
    CATARACT (a complete opacity of the lens). A cataract is a different problem that is also characterized by a cloudy lens. While a cataract is an abnormality that can cause blindness and irritation inside the eye, nuclear sclerosis is normal for an older dog, and the condition usually does NOT interfere with vision! There is no medical treatment that will cure wither a cataract or nuclear sclerosis. Surgical removal of a cataract may be indicated to regain vision, but surgical removal of a lens with nuclear sclerosis would not be helpful.

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