Abbey Holtman, DVM
Glaucoma is a condition in which the intraocular pressure (pressure within the eye) is higher than normal. The classic symptom of glaucoma is a red and painful eye, but other eye diseases can present this way. It is important to understand that if glaucoma is left untreated, the pressure within the eye will continue to elevate and can cause permanent blindness.
Additional clinical signs of glaucoma can include redness of the vessels at the edge of the eye (presenting as redness along the sclera or white portion of the eye), decreased vision, eye pain (as seen by guarding the eye or squinting), tearing, or holding the eyelids closed. Unless both eyes are affected, vision may not be affected. Pets may also have other systemic signs from the pain, including anorexia (lack of appetite), lethargy or decreased activity, depression, or may sleep more. The pain from glaucoma may be comparable to migraine headache pain in people.
Figure 1. Anatomy of the Eye (Vet Learn)
Glaucoma is caused by a blockage of aqueous humor. Aqueous humor is a fluid within the anterior chamber of the eye. The anterior chamber separates the cornea from the lens in the front part of the eye ball (Figure 1). Fluid normally drains from this region constantly, but with glaucoma an obstruction occurs. This causes the fluid to build up and, therefore, the pressure within the eye increases.
We classify the cause of glaucoma as either primary, a problem with the flow of aqueous humor directly, or secondary, due to underlying disease which affects the flow of aqueous humor. Secondary causes can include uveitis (inflammation/infection within the anterior chamber of the eye), luxation (displacement) of the lens, bleeding within the eye, or a tumor within the eye. Primary glaucoma is a bilateral disease, meaning both eyes will become affected.
Both dogs and cats can develop glaucoma. Certain dog breeds are predisposed to developing primary glaucoma, although any breed can be affected. Predisposed breeds include the cocker spaniel, bassett hound, artic breeds, and shar pei. Dogs typically have a more acute or sudden onset, while cats can have a gradual, progressive onset and have secondary glaucoma.
Diagnosis is made by assessing the intraocular pressure, also known as IOP. This can be measured by veterinarians with simple, non-invasive tests. This value is interpreted along with clinical signs and additional findings noted on a complete eye exam. The intraocular pressure can fluctuate throughout the day or with handling/stress. One elevated value without additional signs does not necessarily indicate glaucoma. The opposite is true, as well.
Diagnosis and treatment of glaucoma is needed on an emergency basis. If left untreated for more than 48 hours, medication may not help and blindness may be permanent. Emergency treatment can help preserve vision and help control the pain associated with glaucoma. Medical therapy includes topical eye medications, as well as oral medications. Some patients may require hospitalization for injectable medications based on their level of pain and value of IOP.
Once medical treatment is started for primary glaucoma, pets will need routine monitoring. These medications will be needed life-long. Remember, with primary glaucoma, this is a bilateral disease. Typically, once glaucoma is diagnosed in one eye, treatment is started in the other eye. We may be able to post-pone the development of glaucoma in the other eye, but not prevent it. Even with appropriate diagnosis and treatment, vision may still be lost.
Surgery may be an option, as well, for primary glaucoma. Surgical options are based on whether the eye is visual or not. If the eye is visual, surgery is focused on destroying the cells that produce aqueous humor. This will help control the IOP and can provide pain relief. The effect on vision depends on the amount of damage present prior to surgery. If the eye is blind, the eye can be removed to provide permanent pain relief. An implant can be placed for cosmetic reasons. Blind and pain controlled pets can lead happy and healthy lives.
With secondary glaucoma, treatment is aimed at correcting the underlying cause. Medical and/or surgery may be indicated.
Overall, any eye changes should be addressed immediately on an emergency basis. The faster these problems are diagnosed and treated, the more successful we are at maintaining vision within the eyes.
Dr. Abby Holtman is an emergency veterinarian at Aspen Meadow Veterinary Specialists. AMVS is a 24-hour veterinary facility providing specialty internal medicine, surgery, neurology, oncology, emergency and critical care, physical rehabilitation, and blood bank services for pets. They are located in Longmont at 104 S Main St. For more information, go to www.AspenMeadowVet.com.