Siamese cat Glaucoma
Case of the Month
A 12 year old, female spayed, Siamese cat named Sophie presented for a 3-month history of what the owners described as red eyes and very dilated pupils. A general physical examination was unremarkable and revealed no significant abnormalities. An ocular examination was performed and revealed decreased pupillary light reflexes in both eyes and a decreased menace response in both eyes (blinking of the eye as a reaction to a visual stimulus). The pupils were mydriatic (dilated). The conjunctiva was hyperemic. A fundic (back of the eye) exam was within normal limits. Tear testing and corneal staining revealed no abnormalities. Concern for primary glaucoma was discussed and it was recommended that Sophie have her pressures checked. Bloodwork was performed and was within normal limits. After consultation with the ophthalmologist, Sophie was diagnosed with primary glaucoma. Intraocular pressures were determined to be elevated at 35mmHg in the left eye, and 37mmHg in the right eye. Topical medications were initiated for primary glaucoma (as no underlying issues were detected in the eye). At a recheck appointment 1-week later, intraocular pressures were measured at 22mmHg and 20mmHg in the left and right eye respectively (normal pressures). Currently, a few months later, Sophie receives topical medications daily and is doing well, although her owners report her vision has decreased significantly.
Glaucoma is a disease of the eye seen in both cats and dogs that is characterized by elevated intraocular pressure. It can be a primary disease process where there is an inherent anatomic or biochemical abnormality affecting fluid drainage from the eye, or it can be secondary to another disease process within the eye. Within the eye, there is a clear fluid called aqueous humor that sits in the anterior chamber between the iris and the pupil. Normal pressure is maintained in the eye by a balance of production of fluid and drainage of fluid. When there is a problem with drainage, the pressure within the eye can increase resulting in glaucoma.
Glaucoma, although can be seen in both species, occurs more frequently in dogs than in cats. Primary, hereditary, breed related glaucoma is seen most commonly in purebred dogs (cocker spaniels, beagles, and shih tzu’s, to name a few). In cats, glaucoma is typically secondary to underlying ocular disease. Primary glaucoma in cats is rare but Siamese and Burmese cats may be predisposed. Glaucoma can be a very painful disease for pets, and can eventually lead to blindness. An affected eye may appear normal to an owner when the disease is mild. Early signs of glaucoma include red eyes, a cloudy cornea, dilated pupils, and blepharospasm (squinting). Overtime, glaucoma can cause the eye to increase in size and it may bulge. In severe cases of glaucoma, the eye is often permanently blind by the time of diagnosis. It can also be tough to catch early because pets may appear normal to owners if they have lost vision in only one eye.
Diagnosis of glaucoma is achieved by measuring the intraocular pressure using an instrument called a tonometer. Normal pressure in dogs and cats is 10-25mmHg and pressures above 25mmHg indicate glaucoma. A complete ocular exam (including tear testing, corneal staining, corneal examination, anterior chamber examination, and fundic examination) is important in determining whether underlying ocular disease is present and discerning between primary and secondary glaucoma.
Treatment of glaucoma is lifelong and diligence and consistency with treatment is very important. There are numerous topical medications for glaucoma aimed at decreasing pain, increasing drainage, and decreasing fluid production to manage the intraocular pressure. Treatment of any underlying cause of secondary glaucoma is important as well (i.e. uveitis). Some cases of primary glaucoma are also treated with surgery. If primary glaucoma is diagnosed in one eye, it is common for the other eye to be started on preventative medication. Sometimes it is recommended that enucleation (removal of the eye) be performed. This usually occurs in animals with blind eyes where the glaucoma (or underlying disease) is not responsive to medications, or in an animal with an ocular tumor. Unfortunately, in most cases, glaucoma is not curable and once vision is lost it is permanent. Animals with primary glaucoma often lose vision over time even with appropriate treatment. The prognosis for secondary glaucoma is highly dependent on the underlying cause and its response to treatment.