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Glaucoma is increased pressure within the eye. Cells inside the eye produce a clear fluid (“aqueous humor”) that maintains the eye’s shape 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 continue producing fluid, resulting in increase eye pressure, which can actually can cause the eye to stretch and enlarge, in addition to blinding the eye. Glaucoma is not limited to humans – it can affect your pets, too!
Glaucoma is classified as either primary or secondary in animals. Primary Glaucoma is an inherited condition, occurring breeds ranging from American Cocker Spaniels and Basset Hounds to Chow Chows, Shar Peis, Labrador Retrievers, and Arctic Circle breeds (Huskies, Elkhounds, etc). Touhg it is rare in cats, it can occur and is usually secondary to chronic uveitis. Primary Glaucoma generally begins in one eye, but in most pets, 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, eye cancer and chronic retinal detachment.
Determining if your pet has primary or secondary glaucoma is important, as both the treatment and prognosis vary for each type. (Many pet insurance policies cover the tests and specialists needed to evaluate your pet, so consult your provider.) Veterinary ophthalmologists use slit lamp biomicroscopy, indirect ophthalmoscopy, and gonioscopy to determine the type and cause of glaucoma in your pet. Gonioscopy can help to determine how predisposed your pet’s remaining visual eye is to develop glaucoma when primary glaucoma is suspected. This test involves placing a special contact lens on the eye, allowing examination of the drainage; it is usually performed under sedation or anesthesia.
Glaucoma can affect the eye(s) of your pet(s) in the following ways:
o 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 eye pressure 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;
o 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;
o Pain – Increased intraocular pressure is painful. Dogs, cats (and even human) have normal intraocular pressures between 10-20 mmHg. Glaucoma often results in pressures 45-65 mmHg in dogs and cats, which is significantly higher than in humans with glaucoma, making it much more painful for your pet. The pain persists in the form of a constant headache or migraine. This discomfort can result in lethargy, irritability, or decreased appetite, but is often unapparent to the owner, so be observant!
The only way to ascertain if your pet is suffering from 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 average timeframe for another attack to occur in the remaining eye is 8 months; preventative medical therapy for the “good” eye delays the onset of glaucoma by almost 23 months.
Since glaucoma occurs because fluid is not draining from the eye fast enough, the logical treatment is to open up the drain, however, opening – and keeping open – the drain is difficult. Therefore, many glaucoma therapies are also aimed at decreasing fluid production by the eye.
Medical Therapy – While there are various eye drops and pills that help decrease fluid production or increase fluid drainage from your pet’s eye, they rarely control glaucoma long-term. Consequently, they are used mostly to help prevent/delay glaucoma’s onset 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 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 your pet a partially artificial eye, or an injection into the eye that kills the fluid-producing cells and reduces the pressure.
The best procedure 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. The key to having the best chance of preserving vision is early detection and regular ophthalmic examinations.
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Source by Dr. Jack Stevens
