Glaucoma is a disease characterized by an increase in pressure in the eye (intraocular pressure, IOP) with subsequent blindness. You may notice an enlarged eye, redness, cloudiness, disorientation, lethargy, and/or inappetence. High eye pressures cause pain similar to severe headache or migraines when described by humans with glaucoma. Regarding how the eye pressure is generated, the eye can be considered equivalent to a sink, with a faucet that produces the fluid, and a drain that removes the fluid. The “faucet” is the ciliary body, a part of the eye behind the iris that makes aqueous humor, the fluid that fills the front of the eye. This fluid then drains out of the eye via a drainage angle that exists as a ring on the outer edge of the iris. If the drain is obstructed, the pressure in the eye increases.
Glaucoma can be primary or secondary. In primary glaucoma, there is a defect in the angle (the “drain”). Predisposed breeds include but are not limited to cocker spaniels, bassett hounds, beagles, Chinese shar pei, chow chows and Jack Russell terriers. Secondary glaucoma is when something blocks or clogs a normal angle. Causes include inflammation, tumors, trauma, and lens luxations. Acute glaucoma is an emergency. If the pressure remains elevated for more than a few hours, permanent vision loss can occur. The disease is difficult to treat but several options are available. Options are considered based on whether the patient still has vision, overall health of the patient, financial considerations, etc.
The main goals of treating glaucoma are to preserve vision and alleviate pain. A combination of two to three topical medications is the mainstay of treatment. The first medications, dorzolamide and timolol, prevent production of fluid within the eye. The second medication, latanoprost, improves drainage of fluid from the eye. These medications are used two to three times daily to keep the pressure from increasing inside the eye. Other topical or oral medications may be indicated depending on exam findings. Unfortunately, all patients eventually fail medical management of glaucoma and require surgery to maintain comfort after they go blind. Options include enucleation (removal of the eye), intra-scleral prosthesis (replacing the contents of the eye with silicone), or ciliary body ablation. There are pros and cons to each of these treatments.
End stage glaucoma
Once the eye is blind and painful, our goals become comfort for the patients. Options include enucleation (eye removal), evisceration (intrascleral prosthetic, ISP), and chemical ciliary body ablation.
Enucleation and evisceration
Enucleation and evisceration are performed under general anesthesia, while a chemical ciliary body ablation is performed under sedation. With enucleation, the globe is removed and the eyelids are sutured shut. Sometimes an orbital prosthetic can be placed to prevent indentation of the eye socket – however, we often do not want to place a prosthetic when infection or neoplasia is present.
The second option is an intrascleral prosthetic. This prosthetic is placed within the fibrous capsule (cornea and sclera) that once held the eye contents. Surgery involves an incision into the eye, and removal of the contents within the eye. A silicone prosthetic is then placed into the empty globe, and the eye sutured. A temporary tarsorrhaphy (partial closure of the eyelids) is generally placed to help protect the eye as it is healing.
Intrascleral prosthetic is the most aesthetically pleasing option, however it makes no difference to the patient. Prosthetics have an increased risk of infection and implant rejection; however, these risks are low. Patients are also at risk for dry eye and corneal ulcerations throughout their life, as they are thought to have decreased corneal sensation, and cannot protect it as a dog with normal corneal nerve endings can.
Chemical ciliary body ablation
The third option is a chemical ciliary body ablation. This is generally performed under sedation and involves instilling an injection of a toxic antibiotic (gentamicin) and small amount of steroid (dexamethasone) into the back portion of the eye. This antibiotic kills any cells that produce fluid within the eye, but also destroys any cells that provide vision. It is about 85% successful in dogs, and tends to be less successful in patients with significant inflammation. If the procedure fails, it can be tried again, with an approximately 50% success rate. Following failure of the first or second injection, enucleation or placement of an intrascleral prothesis would be recommended. If the eye responds to the injection, the pressures are often controlled within 1-2 weeks. Sometimes the eye can fill with blood, or shrivel up as the pressure continues to decrease further. Patients are also still at risk for dry eye and corneal ulcers long term, as the globe remains within the socket. If complications develop, eye removal may be recommended.
Post-operative care of an enucleation includes antibiotics, anti-inflammatories, and pain management. Care for an evisceration and ISP also includes topical antibiotics and lubrication. Glaucoma medications are generally continued following gentamicin injection, plus antibiotics. Pressures are rechecked in two weeks, and if controlled, glaucoma medications are slowly weaned.