By Ralph Hamor, DVM, MS, DACVO
Glaucoma is the leading cause of blindness in middle-aged dogs. For this reason, glaucoma should be on your list of differentials for any animal with red or watery eyes, especially for breeds that are predisposed to glaucoma, such as basset hounds, chow chows, cocker spaniels, fox terriers, Jack Russell terriers, and shar peis.
You may be surprised that a “safe” intraocular pressure has not been defined for the dog and cat, though normal range for most domestic species is 12 to 24 mmHg. Once pressure-induced damage of the retina and optic nerve has occurred, even pressure in the “normal” range may cause further damage.
Primary glaucoma occurs because of a congenital or acquired abnormality of the drainage angle or a malfunctioning drainage angle.
At the Veterinary Teaching Hospital we have highly specialized tools to evaluate the drainage angle and help confirm a diagnosis of primary glaucoma.
For primary glaucoma, the immediate treatment goal is to reduce the patient’s intraocular pressure to prevent permanent blindness. Medical treatment is directed at opening the drainage angle, decreasing ciliary body aqueous production, and increasing aqueous outflow. The “normal” eye should always be prophylactically treated with medications in order to delay onset of glaucoma. Intraocular pressure in the normal eye should be closely monitored.
Unfortunately, almost all dogs with primary glaucoma will eventually be blind in both eyes, although medical and surgical treatment may extend the visual life of the eye.
Treatment for glaucoma that occurs secondary to another disease process—such as uveitis, lens luxation or subluxation, swollen lens, or malignant glaucoma—should target the primary cause while including glaucoma therapy.
In cats glaucoma is almost always secondary to chronic intraocular inflammation. Aqueous humor misdirection, a syndrome in cats, may be treated medically or with surgical removal of the lens. Only secondary glaucoma has the potential for a cure without surgical intervention.
Glaucoma cannot be diagnosed or treated without the use of a tonometer. I highly recommend that every private practice invest in this piece of equipment, which costs around $3,000.
Questions for the ophtho service? Email firstname.lastname@example.org.