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Glaucoma: a painful condition in some dogs/cats
Speedy diagnosis and intervention can save vision and ease pain
Glaucoma, or an increased intraocular pressure (pressure within the eyeball), is a painful condition in dogs and cats that can lead to blindness. In human medicine, glaucoma describes a multitude of diseases that affect the optic nerve and can occur even in patients with normal intraocular pressure, however in dogs and cats the pressure is always increased. Again, glaucoma is extremely painful in pets, and if untreated even for a day or two can lead to vision impairment and even permanent blindness.
How does the eye maintain its normal pressure in the healthy pet? The eye is divided into two chambers: the anterior chamber (the portion in front of the pupil) and the posterior chamber (the portion behind the pupil). The fluid that keeps the eyeball at its normal pressure is called aqueous humor. Aqueous humor is produced by glands known as ciliary bodies. The ciliary bodies are located in the posterior chamber and the fluid that is produced flows through the pupil into the anterior chamber. From there it exits the eye through an opening between the cornea and iris called the iridiocorneal angle and then into the circulation.
What goes wrong in patients who develop glaucoma? Either the patient produces too much aqueous humor (this is not seen in dogs or cats) or the patient cannot drain the fluid at a proper rate (this is seen exclusively in dogs and cats).
What would interfere with normal drainage of the aqueous fluid? Primary glaucoma refers to a patient that was born with an abnormality within the eye that would reduce drainage of the fluid produced. There is either a very narrow iridocorneal angle (known as closed angle glaucoma) or something blocking the flow through this area even if the angle is normal (open angle glaucoma). Secondary glaucoma refers to a patient born with a normal eye but changes occur over time. These include trauma to the eye, infections, diabetes and tumors of the eye itself.
How do I recognize glaucoma in my pet? Luckily, glaucoma is pretty rare in dogs and cats compared to other eye conditions, however early recognition and immediate treatment are imperative for saving sight. Glaucoma is painful, therefore you will first notice pain, swelling and squinting of the eye that is affected. An increased pressure within the eyeball paralyzes the pupil and will cause it to dilate. These are signs that pet owners should visit the veterinarian immediately.
When your veterinarian examines your pet's eye, he or she will probably want to measure an intraocular pressure (IOP). The old way to measure intraocular pressure was with an instrument called a Schiotz tonometer (named after the doctor that invented this instrument). This is still considered the most accurate way to measure IOP, however there are newer digital tonometers that are much easier to use and almost as accurate. We have one at my clinic and every colleague in the area that I know has one as well.
How is glaucoma treated? Although glaucoma is almost always treated in the emergency situation with medications, surgical intervention by a specialist (veterinary ophthalmologist) is necessary. Medical treatments are designed to reduce the IOP by either decreasing aqueous humor production or increasing drainage. Follow up surgical intervention will include procedures such as shunts through the iridicorneal angle to increase drainage, destruction of a portion of the ciliary body to reduce aqueous humor production, or a combination of both procedures.
Cases of glaucoma that have gone unrecognized, untreated, or both for a period of time will usually result in loss of vision in that eye. In cases of chronic glaucoma with blindness in the affected eye, therapy is directed towards making the patient comfortable. In these cases sometimes enucleation, or removal of the eye, is the best option.
Remember, if your pet is diagnosed with glaucoma and your veterinarian is urging you to see a specialist, sooner is definitely better than later.
Thank you again to Ellen Barcel and the rest of the staff at the Times Beacon Record for another great year of articles. Best holiday wishes and a happy new year to all of my readers (both on two and four legs).
Dr. Kearns is a veterinarian with a special interest in emergency and critical care. He has been in practice for eight years. Dr. Kearns is pictured here with his son Matthew and his cat, The One Eyed Guy.