Glaucoma is defined as an elevated pressure within the eye. If glaucoma is uncontrolled, the pressure will cause irreversible damage to the retina and optic nerve. This damage leads to blindness and can occur rapidly.
There is a constant fluid production within the eye. This fluid serves vital roles such as providing nutrition to the internal ocular structures. The drainage angle is a structure located inside the eye at the outer edge of the iris (the colored part of the eye). The drainage angle can be compared to the drain in your sink, which has holes that allow removal of fluid from the eye into the bloodstream. The constant production and outflow of fluid achieve a balance so that the normal pressure within the eye is maintained between 10 and 25 mmHg. Most cases of glaucoma in animals are due to compromise to the drainage angle of the eye. If the “drain holes” are compromised, the fluid is still being produced within the eye but cannot escape. Eventually, the intraocular pressure rises and the signs of glaucoma develop.
Redness of the white part of the eye
Squinting of the eye, indicating ocular pain
Cloudiness of the eye
Loss of vision
Enlargement of the eye
Note: Not all of these signs will be present in every glaucoma patient!
The most common cause of glaucoma is a primary abnormality at the drainage angle of the eye, which is usually genetic in origin. Certain breeds are at higher than normal risk for glaucoma, including the Cocker Spaniel, Chow Chow,
Shar Pei, Bassett Hound, and Siberian Husky. Although the underlying lesion is considered a hereditary one and affected dogs are usually born with the underlying abnormality, the clinical signs of glaucoma do not usually appear until middle age.
Glaucoma can also develop secondary to another problem within the eye such as a tumor, inflammation, trauma, or lens dislocation (luxation).
A thorough examination of the eye is necessary in order to determine the cause of glaucoma and to determine the degree of damage to the eye from the elevated pressure. The intraocular pressure is measured with a tonometer and the drainage apparatus of the eye might be evaluated with a special type of lens applied to the eye (gonioscopy).
Glaucoma is more than just elevated intraocular pressure so follow-up full eye examinations are important. Accurate monitoring cannot be based on intraocular pressure alone.
The management of glaucoma depends on the cause and the length of time that the glaucoma has been present. If there is potential for vision, a procedure (an IV injection or drainage of fluid from the eye) might be performed to rapidly decrease the pressure within the eye. Medical therapy consists of eye drops and/or pills designed to lower intraocular pressure.
Primary glaucoma is a serious disease, which eventually become refractory to medical therapy in most cases. Surgery is usually required to maintain vision long-term. The long-term visual prognosis is guarded though the newest laser technology offers greater hope for these difficult cases. Laser surgery is generally the best surgical option for visual eyes with poorly-controlled glaucoma. The most common complications from surgery are excessive inflammation and pressure fluctuations during the early recovery period.
We are commonly asked why any procedure is needed at all for uncontrolled glaucoma if it is already a blind eye. The reason is that uncontrolled glaucoma is a painful disease whether the eye is visual or not. Though signs of pain are not detectable in some pets with chronic glaucoma, we feel that most are indeed painful based on how they improve after the glaucoma is controlled medically or resolved by surgery. The best options for a blind, glaucomatous eye are intraocular prosthesis, enucleation, or intraocular injection (ciliary ablation).
1) Intraocular prosthesis: This usually produces the most natural and cosmetic outcome. The prosthesis is permanent and does not require any care. The most common problems that can occur with prosthetic eyes are any surface diseases of the eye (corneal ulcers and dry eye) as the cornea and conjunctival tissues are retained with this approach. After surgery, all glaucoma medications are discontinued on that eye. Some patients are not ideal candidates for this approach.
2) Enucleation (complete eye removal): This surgery resolves the glaucoma, allows a biopsy to be performed, and no glaucoma therapy will be required postoperatively (on that eye). In many cases, an orbital implant is placed. This type of implant is not visible to you as it is underneath the skin. It improves the cosmetic outcome though it is not an option in all cases.
3) Intraocular injection (ciliary ablation): With this approach, the appearance of the eye is less predictable long-term, as the eye can gradually decrease in size and will appear cloudy due to cataract and/or corneal scarring. This is the least invasive option but it is only successful 80-90% of the time (with primary glaucoma; success rate lower with secondary glaucoma).
4) Laser surgery: We are pleased to be able to offer you the newest in glaucoma technology-endoscopic cyclophotocoagulation (endolaser). This involves lasering of the ciliary processes of the eye (tissue that produces fluid within the eye) through a tiny endoscope that is introduced into the eye after lens removal. The recovery period can be intense but many of these dogs eventually come off all glaucoma medications and long periods of glaucoma control are commonly achieved. In some cases, a shunt is placed in the eye at the same time to help during the initial recovery period. If this option is being considering for your pet, you should also read our Endolaser Surgery handout. Although this procedure can be performed on blind eyes, it is usually reserved for visual eyes.
Unfortunately, other than surgery, there is no permanent cure for glaucoma. The long-term prognosis for maintaining vision in dogs with primary (heritable) glaucoma is poor. In an attempt to preserve vision, regular recheck appointments are very important to monitor trends of the intraocular pressure. This allows modification of medical therapy as needed.
The clinical signs of glaucoma may develop in only one eye initially. The other eye is generally prone to glaucoma and requires prophylactic treatment to delay the onset of glaucoma. If glaucoma is untreated, irreversible blindness can occur within 24 hours. GLAUCOMA IS AN EMERGENCY! Early detection and treatment of glaucoma are critical to preservation of vision.
If you feel that your pet’s glaucoma is out of control or if you run out of glaucoma medication, we need for you to call or page (if after hours) right away. Do NOT wait until the next business day.