Glaucoma is increased pressure within the eye. Cells inside the eye produce a clear fluid ("aqueous humor") that maintains the shape of the eye and nourishes the tissues inside the eye. The balance of fluid production and drainage is responsible for maintaining normal pressure within the eye. In glaucoma, the drain becomes clogged but the eye keeps producing fluid. Therefore, the pressure in the eye increases. The increased pressure in the eye actually can cause the eye to stretch and enlarge, in addition to blinding the eye.
Glaucoma is classified as either primary or secondary in animals.
Primary Glaucoma is an inherited condition. Primary glaucoma occurs in many breeds, especially American Cocker Spaniels, Basset Hounds, Chow Chows, Shar Peis, Labrador Retrievers, and Arctic Circle breed dogs (Huskies, Elkhounds, etc). It is rare in cats.
Primary Glaucoma usually begins in one eye, but in most patients it eventually involves both eyes, leading to complete blindness.
Secondary Glaucoma occurs when other eye diseases cause decreased fluid drainage. Common causes of secondary glaucoma are inflammation inside the eye (uveitis), advanced cataracts, cancer in the eye, lens subluxation or luxation, and chronic retinal detachment. Glaucoma in cats is usually secondary to chronic uveitis.
Determining if your pet has primary or secondary glaucoma is important because the treatment needed and the prognosis for vision is different for each type. Veterinary ophthalmologists use slit lamp biomicroscopy, indirect ophthalmoscopy, and gonioscopy to determine the type and cause of glaucoma in your pet. Gonioscopy helps determine how predisposed the remaining visual eye is to develop glaucoma when primary glaucoma is suspected. This test involves placing a special contact lens on the eye, which allows examination of the drainage angle. Gonioscopy is usually performed under sedation or anesthesia.
Vision Loss. Pressure damage to the optic nerve and decreased blood flow to the retina, the "film in the camera," results in loss of vision. However, if the pressure in the eye remains uncontrolled, the retina degenerates and vision is permanently lost. Permanent blindness can occur within several hours if the pressure is very high and the glaucoma develops rapidly.
Unfortunately, the first eye to develop primary glaucoma in dogs is usually already blind by the time the disease is recognized. For this reason, treatment in these cases is directed at relieving discomfort in the blind eye and preventing or delaying glaucoma development in the other eye. Gonioscopy of the remaining visual eye helps determine how to treat this eye.
Pain. Increased intraocular pressure is painful. Dogs, cats, and humans have normal intraocular pressures between 10 and 20 mmHg. Glaucoma often results in pressures of 20-28 mmHg in humans, but pressures of 45-65 mmHg are common in dogs and cats. For this reason, glaucoma in pets is more painful than glaucoma in humans. The pain persists in the form of a constant headache or migraine. This discomfort can result in decreased activity, less desire to play, irritability, or decreased appetite, and is often not apparent to the owner. Your pet will not tell you the eye is uncomfortable.
The only way to know for sure if your pet has glaucoma is to have the intraocular pressures measured by a veterinarian. Signs of glaucoma can include a red or bloodshot eye and/or cloudy cornea. Vision loss is also characteristic of glaucoma. However, loss of vision in one eye is often not obvious because animals compensate with their remaining eye. Eventually, the increased pressure will cause the eye to stretch and become enlarged. Unfortunately, eyes are usually permanently blind by the time they become enlarged.
If your dog has lost one eye to Primary Glaucoma and the other eye is at risk of developing glaucoma: The median time until an attack occurs in the other eye is 8 months. Prophylactic medical therapy for the remaining eye delays the onset of glaucoma from a median of 8 months to a median of 31 months.
How is Glaucoma treated?
Since glaucoma occurs because fluid is not draining from the eye fast enough, the logical treatment is to open up the drain. Unfortunately, opening the drain and keeping it open is difficult. Therefore, many glaucoma therapies are also aimed at decreasing fluid production by the eye.
A PERFECT SOLUTION FOR GLAUCOMA DOES NOT EXIST! AND . . . GLAUCOMA IS AN EXPENSIVE LIFETIME DISEASE TO TREAT, ESPECIALLY GENETIC GLAUCOMA IN DOGS.
Medical Therapy. There are several different types of expensive eye drops and pills that help decrease fluid production or increase fluid drainage from the eye. While these medications are helpful in animals, they usually do not control glaucoma long term. Consequently, they are used mostly to help prevent or delay the onset of glaucoma in the remaining visual eye, and as temporary treatment until surgery can be performed in the affected eye.
Surgical Therapy. The type of surgical procedures available for glaucoma depends upon whether the eye still has the potential for vision. For visual eyes, intraocular pressure can be reduced by performing a cycloablation procedure and a drainage implant procedure. For permanently blind eyes, the eye can be removed (enucleated) with the option of placing a sterile prosthetic ball implant in the eye socket prior to skin closure, an implant placed inside the eye giving the pet a partially artificial eye, or an injection of a drug into the eye that kills the fluid-producing cells and reduces the pressure.
THERAPY FOR POTENTIALLY VISUAL EYES:
Cycloablation Surgery and Drainage Implant Surgery FOLLOWED BY Lifetime Medical Therapy
Cells in the eye that produce fluid are killed surgically. To help control pressure for the first few weeks after surgery, a drainage tube is sometimes implanted into the eye. 30% of dogs will require additional surgeries. Performed at Animal Eye Care.
Lifetime Medical Therapy Alone
Oral and topical medication to control intraocular fluid production and increase fluid drainage.
SURGICAL THERAPY FOR BLIND EYES:
Removal of the eye and the eyelids are sutured closed. Usually performed by your family veterinarian.
Enucleation and Orbital Prosthesis (not recommended for cats)
Removal of the eye. A black prosthetic ball is then placed in the orbit and the eyelids permanently closed. Prevents "sunken-in" appearance of skin over eye socket. Performed at Animal Eye Care.
Evisceration and Intrascleral Prosthesis
The inside contents of the eye are removed and replaced with a prosthetic ball. This leaves your pet with a gray, non-painful eye that has no vision, but blinks and moves. Performed at Animal Eye Care.
Intravitreal Gentamicin Injection (not recommended for cats)
The antibiotic gentamicin is injected into the eye, which kills the cells that produce aqueous humor. This usually causes the eye to become cloudy, and 50% will markedly decrease in size. Occasionally, some eyes will bleed inside, but this is not uncomfortable.
Which procedure is best for your pet depends on the type of glaucoma, the potential for vision, and your preference for the cosmetic appearance of your pet's face. Glaucoma is a very frustrating disease because it requires constant monitoring, may require several different therapies, has a high cost financially, and despite excellent care often still results in permanent vision loss. The key to having the best chance of preserving vision is early detection and regular ophthalmic examinations.
Please remember: Glaucoma can cause blindness in spite of our best efforts. A high level of commitment to treatment and regular ophthalmic examinations is required to have the best chance of preserving vision. If your pet is diagnosed with primary glaucoma, please notify the dog's breeder. They need to know!
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