Definition:
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.
Anatomy/Physiology:
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.
Clinical Signs:
Redness of the white part of the eye (sclera)
Squinting of the eye, which indicates ocular pain
Cloudiness of the eye
Dilated pupil
Loss of vision
Enlargement of the eye
Note: Not all of these signs will be present in every glaucoma patient!
Causes:
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).
Examination:
A thorough examination of the eye is necessary in order to determine the cause of the glaucoma and to determine the degree of damage to the eye from the elevated pressure. The intraocular pressure is measured with an instrument called a tonometer and the drainage apparatus of the eye might be evaluated with a special type of lens applied to the eye (gonioscopy).
Monitoring :
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.
Treatment:
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.
Surgery:
Glaucoma is a severe disease, which eventually becomes refractory to medical therapy in most cases. Surgery is usually required in order to maintain vision. The long-term prognosis for vision is guarded, however. Laser surgery is the least invasive surgery for control of glaucoma and has the highest success rate for maintaining a normal intraocular pressure in visual eyes. The most common complications that can result from laser surgery are a transient, postoperative pressure increase and corneal ulceration. Laser surgery might eventually fail, but it can be repeated as needed.
In eyes that are irreversibly blind, surgery should be considered in order to prevent or eliminate ocular pain. The options include:
1) Intraocular prosthesis: This is the most cosmetic option. The prosthesis is permanent and does not require care by the owner. After surgery, glaucoma therapy can be discontinued. Approximate cost - $1320-1665
2) Intraocular injection (gentamicin injection/ciliary ablation): The appearance of the eye is unpredictable long-term, as the eye can gradually decrease in size and will appear cloudy (cataract). This is one of the least invasive options, but it is only about 80% successful. Approximate cost – $500-725
3) Enucleation (complete eye removal): This surgery cures the glaucoma, allows a biopsy to be performed, and no glaucoma therapy will be required post-op (on that eye). Approximate cost - $1155-1510. (Extra if biopsy recommended/performed).
4) Laser surgery: This is a non-invasive surgery, but will generally need to be repeated every 9-18 months. Medical therapy is usually required after surgery. Approximate cost - $1205-1440. There is an additional charge if a shunt is placed.
Prognosis:
Unfortunately, there is no permanent cure for glaucoma other than surgery. 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 prone to glaucoma (if a primary glaucoma case) 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.
