Glaucoma is increased intra-ocular pressure (IOP) in the front chamber of the eye. The size and shape of a normal eye is maintained by the amount of fluid (aqueous humor) within the eyeball. Fluid is constantly produced and drained within the eye in equal amounts to maintain a constant, normal, functional pressure. Glaucoma is caused by inadequate drainage of the aqueous humor, as opposed to over-production.
Glaucoma can be classified as primary or secondary. Primary glaucoma results in increased IOP in a healthy eye. It is usually caused by an inherited anatomical abnormality in the drainage angle of the eye. Secondary glaucoma results in increased IOP due to disease or injury. Causes include uveitis (inflammation) and infection of the eye, dislocation of the lens, tumors, intra-ocular bleeding, and lens damage.
Symptoms of glaucoma can include squinting of the eye, rubbing at the eye, watery eye discharge, depression or lethargy, bulging of the eye, eye redness, cloudy/bluish eye and blindness.
There are 42 breeds of dog that are more prone to developing primary glaucoma than others. They are the Afghan, Akita, Alaskan Malamute, Basset Hound, Beagle, Border Collie, Boston Terrier, Bouvier des Flandres, Cairn Terrier, Cardigan Welsh Corgi, Chihuahua, Chow, Cocker Spaniel, Dachshund, Dalmatian, Dandie Dinmont Terrier, English Springer Spaniel, Giant Schnauzer, Great Dane, Maltese, Manchester Terrier, Miniature Pinscher, Norfolk Terrier, Norwegian Elkhound, Norwich Terrier, Pembroke Welsh Corgi, Poodle, Saluki, Samoyed, Scottish Terrier, Sealyham Terrier, Shih Tzu, Siberian Husky, Smooth-Coated Fox Terrier, Tibetan Terrier, Welsh Springer Spaniel, Welsh Terrier, West Highland White Terrier, Whippet, and Wire-haired Fox Terrier.
IOP should be checked annually in every dog with a breed predisposition to glaucoma. IOP should also be checked in every dog or cat that has a red conjunctiva or red sclera, as this is one of the first symptoms of glaucoma, and early detection and treatment is key. In addition, IOP should be measured in every dog or cat that has suffered head or eye trauma, has a painful or squinting eye, and in all senior pets. IOP is measured using a specialized tool called a tonometer. The surface of the eye is numbed using a few drops of a liquid anesthetic, and the tip of the tonometer is tapped against the surface of the eye. Six readings are performed per eye and then averaged together. Normal IOP is 12-25mmHg. In addition, the eye will be examined with an ophthalmoscope, and ocular reflexes may be evaluated. In certain cases referral to a veterinary ophthalmologist may be required for further testing.
Once glaucoma is diagnosed it is imperative to begin treatment immediately. Glaucoma is a PAINFUL condition that causes structural damage within the eye leading to permanent blindness. It is very common for primary glaucoma to develop first in one eye, and then in the other eye, usually within 1 year. For this reason it is very important to begin treatment as soon as a diagnosis is made. Glaucoma can also be the first sign of ocular tumors which should be removed.
The goal of treatment is to treat the underlying cause, relieve chronic pain, and preserve remaining vision by slowing disease progression. Treatment is aimed at normalizing the amount of fluid inside the eye by either increasing the outflow or decreasing the inflow of the aqueous humor. Blindness in one or both eyes is a serious complication of glaucoma, and cannot be helped in some cases. It is important to note that many dogs and cats have a very good quality of life with vision in only one eye, or even vision loss in both eyes. Our pets are generally much more adaptable than we are, and learn to rely on their other senses to navigate their surroundings.
Glaucoma treatment is either medication-oriented or surgical. Medication-oriented treatment usually involves topical medication (drops) or oral medication. 0.5% Timolol is a β-blocker that is administered to the eye three times daily in drop form to decrease IOP. 2% Dorzolamide is a carbonic anhydrase inhibitor administered topically to the eye three times daily in order to decrease the production of the aqueous humor, thus decreasing the IOP. Prednisolone (a steroid) can also be used in cases of uveitis (inflammation of the middle layer of the eye). It is usually administered orally or topically. In addition pain medication such as oral NSAIDs (Non-Steroidal Anti-Inflammatories) or Tramadol (pain medication) are necessary to control chronic pain. In order to determine whether the glaucoma is responding to treatment, tonometry measurements will be necessary once a week. As control is achieved the frequency of testing may decrease to once a month.
Surgical treatment is often necessary when the eye fails to respond to medication. Referral to an ophthalmologist for anterior chamber shunts, laser surgery, lens removal (in the case of lens luxation), and implant surgery is an option that some pet owners may wish to consider. Enucleation (removal of the eye) can be done here at the River Road Veterinary Clinic, and is often the most cost effective option. If the eye is blind and painful and treatment with medication has failed, the pain is likely to persist. In order to end the persistent pain, an enucleation is usually performed.