Affects: Dogs
Canine glaucoma refers to a group of diseases in dogs that affect the optic nerve and involve a loss of retinal ganglion cells in a characteristic pattern. An intraocular pressure greater than 22 mmHg (2.9 kPa) is a significant risk factor for the development of glaucoma. Untreated glaucoma in dogs leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness.
The group of multifactorial diseases which cause glaucoma in dogs can be divided roughly into three main categories: congenital, primary or secondary. In dogs, most forms of primary glaucoma are the result of a collapsed filtration angle, or closed angle glaucoma.
Signs And Symptoms: Glaucoma often goes unnoticed in dogs until it is in a more severe state. There are rarely any symptoms in the early stages of the disease so regular eye checks by qualified veterinary professionals are important. Dogs will sometimes rub the eye if it is painful. An eye affected with glaucoma may be red, swollen, sore, or become clouded in appearance.
Causes: There are three broad categories of causes of glaucoma: congenital, primary and secondary.
Congenital glaucomas are present at birth, although they may not become apparent until the animal is a few months old. These types of glaucoma are due to abnormalities in the structures of the eye which occurred during ocular development. One or both eyes may be affected.
Primary glaucomas occur in the absence of other eye disease, and are therefore presumed to be genetic in origin. The most common type of glaucoma in dogs is primary angle-closure glaucoma (PACG). The least common type of glaucoma in dogs is primary open-angle glaucoma (POAG), although this is the most common type that affects humans. In the Beagle, POAG is an inherited autosomal recessive trait.
Secondary glaucomas occur when other eye diseases alter the flow of aqueous humor either into or out of the eye.
Diagnosis: Veterinarians employ three general methods: tonometry, gonioscopy, and ophthalmoscopy. Tonometry measures the intraocular pressure with an instrument. Normal intraocular pressure in dogs can ranges from 12 to 25 mmHg (1.6 to 3.3 kPa), and both eyes should be similar in pressure. Gonioscopy is a diagnostic procedure to examine the angle of the anterior chamber. Direct and indirect ophthalmoscopy is necessary to evaluate the retina and particularly the optic nerve.
Treatment: There is no cure for glaucoma, so the aims of treatment are to reduce pain in the eye, and to preserve vision. Most dogs are treated medically, although sometimes surgery is required. As the cause of primary glaucoma is often unknown, medical treatment is usually aimed at reducing the main sign of glaucoma (raised intraocular pressure) rather than at treating the cause of the disease.