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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.

There are 2 main types of glaucoma - primary and secondary.

In primary glaucoma, the cause of the increase in ocular pressure is due to deceased outflow from the drainage angle. It is frequently an inherited problem. Beagles, Bassett Hounds, and Cocker Spaniels are especially prone to this type of glaucoma.

In secondary glaucoma, the pressure in the eye is too high because something else is wrong with the eye, such as a lens luxation, bleeding, inflammation, or tumor.

  • a red (bloodshot) eye
  • a painful eye
  • eyelids held shut
  • excessive tearing of the eye
  • eye may appear cloudy or blue
  • sudden blindness
  • a dilated (enlarged) pupil that does not respond normally to light
  • enlargement of the eye
  • appetite loss
  • depression

The type of glaucoma treatment chosen (medical vs. surgical) 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 orally and affect the whole body, while others are put directly in the eye and have a local effect. These drugs help to reduce the amount of fluid produced in the eye, and also to increase the outflow of fluid from the eye. The drugs that work when the problem is first diagnosed and may not work forever. Therefore, the intraocular pressure needs to be monitored on a regular basis so 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.

In some cases, surgical procedures are available that may help provide long-term control of glaucoma. One of these procedures uses a laser to destroy the part of the eye that produces fluid and thereby reduces the pressure inside the eye. Another surgery involves the placement of 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 repeat procedures may be requied over several years 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.

Uveitis is defined as an inflammation of the parts of the eye (uvea) which contain blood vessels, ie. 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 cliliary body and the choroid. (See diagram at top of page.) 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.

The following are signs of uveitis:

  • cloudiness
  • redness
  • small pupil
  • decreased vision
  • painful eye

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 the eye on furniture or the rug
  • holding the eye shut
  • elevated third eyelid
  • decreased appetite
  • depression

There are many causes of uveitis. Diseases such a 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.

To diagnose uveitis the following tests are often performed:

1. Bloodwork - a CBC and chemistry panel
2. Chest radiograph - to look for tumors or pneumonia
3. Abdominal ultrasound - to evaluate the organs
4. Testing for specific diseases based on location and travel (ie. Lyme disease, Rocky Mountain Spotted Fever, etc.
5. Ocular ultrasound
6. Aspirate of fluids inside the eye

Keratoconjunctivitis sicca (KCS) is also called dry eye. This condition is due to a deficiency in tear production that results in a red, itchy eye with thick mucous discharge. The tear production is measured by the Shirmer 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.

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 case of KCS, 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 results in the thickening of the cornea so that it appears dull and cloudy. Tears are made or mucus, water and oils. Cry eye is a deficiency of the watery (or aqueous) part of the tears. Therefore animals with KCS accumulate a lot of mucus.

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 profuse, ropy, thick discharge that adheres to the eye. without treatment, the cornea may eventually pigment and scar to the point of 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.)

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.

How is KCS treated?

Animals with acute dry eye frequently havee 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 forms of KCS are treated by topical tear substitutes as well as stimulation of the existing tear production. Cyclosporine ointment or oily drops is used to increase tear production and reduce inflammation. Sometimes used alone 2x/day this can control the KCS effectively without any other medications. Additionally tacrolimus drops have been used successfully to treat KCS.

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 with antibiotic therapy. Anti-inflammatory drugs are frequently used to help control scarring and irritation.

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

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 expect 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. There is often excessive tearing and small pupils as well.

A corneal ulcer is diagnosed by using fluorescein stain to coat the eye. In a normal eye, the orange stain will wash away when rinsed. In an eye with a corneal ulcer the stain will stick to the ulceration leaving behind a green glow.

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 necessary. The treatment for a corneal ulcer is most often medical with the use of topical pain medications and antibiotics. Deep or infected ulcers may need surgical treatment in addition to topical therapies.

A cataract is an 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 objuects. A thin capsule (the consistency of cellophane) covers the lens.

In front of the lens is a clear fluid called the aqueoud humor, and behind the lens is a clear gel called the vitrious 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.

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.

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 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 7 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 a 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 either 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.

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 simlar to the film in a camera; the image or picture is received on it.

Fig. 1 - Normal Retina

Fig. 2 - Retina showing signs of Progressive Retinal Atrophy (PRA)

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 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.

  • No effective treatment is available
  • Complete blindness eventually results
  • The condition is NOT painful
  • PRA is prevented through selective breeding of animals with normal eyes
  • Poor vision in dim light is the first sign you will see in your dog
  • You may eventually see dilated pupils
  • Sometimes cataracts will develop secondary to retinal degeneration, but because of the retinal degeneration, cataract removal would not help the animal regain vision

Additional ocular conditions will be covered next month in the May 2009 Monthly Update.

Until then, if you think your pet has an ocular emergency please call the Roslyn-Greenvale Veterinary Group at 516-621-4010 to schedule an appointment immediately.

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