Glaucoma is a disease in which elevation of eye pressure causes damage to the optic nerve. The optic nerve contains over 1 million neurons which originate in the retina and transmit vision to the brain. If a sufficient number of these neurons are damaged, loss of vision will occur. The side vision is effected initially. In advanced cases, central vision may be permanently lost.
In a normal eye, clear fluid (aqueous) is produced inside the eye, then drained internally through a structure called the angle. Glaucoma occurs when the drainage of fluid is impeded or slowed, and pressure rises. Glaucoma is more common in older patients, African Americans, and those with a family history of the condition. It sometimes occurs in people with normal eye pressure (normal pressure glaucoma).
TYPES OF GLAUCOMA
Primary
Open-angle glaucoma (OAG) is the most common type of glaucoma, and occurs when aqueous drainage is mildly decreased. The eye pressure slowly increases, but the majority of patients remain asymptomatic. Loss of vision and optic nerve damage are detected during eye examination by the eye doctor.
Closed-angle glaucoma, or narrow-angle glaucoma (NAG), occurs when the drainage angle becomes anatomically closed. Eye pressure rapidly increases and causes severe pain and vision loss. Acute angle closure glaucoma is an emergency.
Secondary
Neovascular glaucoma (NVG) occurs when retinovascular disease induces abnormal blood vessel growth on the iris. This seals the angle and blocks aqueous drainage. NVG causes severe pressure, pain, and vision loss.
Steroid medications can cause elevation of eye pressure and subsequently lead to Steroid-Induced Glaucoma.
Uveitic Glaucoma is caused by an inflammatory condition of the eye called uveitis, which leads to clogging and scarring of the angle. Steroids are used to treat uveitis and may also contribute to eye pressure elevation.
Angle-Recession Glaucoma is the result of blunt trauma to the eye causing damage to the trabecular meshwork, leading to reduced aqueous drainage.
Pigmentary Glaucoma is a condition in which pigment granules break free from the iris and ciliary epithelium, and obstruct the trabecular meshwork.
EVALUATION
Eye Pressure is measured at each visit. Careful examination of the eye for conditions contributing to glaucoma is performed.
Fundus Photographs are taken to document the appearance of the nerve.
Optical Coherence Tomography (OCT) is a scan which measures the neurons of the optic nerve with great detail. It is able to detect glaucoma at its earliest stages, before damage to the vision has occurred. OCT can also visualize the front structures of the eye, including the angle.
Visual Field Testing is performed to assess the overall visual function of the eye. Special attention is directed to the peripheral vision to detect the earliest damage to the patient's vision.
TREATMENT OF GLAUCOMA
Topical Medications
Topical medications (drops) are the mainstay of glaucoma therapy. These medications work either by decreasing aqueous production, or increasing aqueous outflow.
The majority of patients with glaucoma can be effectively managed with drops. Patient compliance and careful monitoring of the eye pressure, visual field, and optic nerve health are vital to preserve vision.
Laser Treatment
Laser treatment is useful to lower eye pressure when drops are not adequate.
Selective Laser Trabeculoplasty (SLT) targets the drainage system of the eye and is effective in lowering eye pressure in most patients. The benefit may be temporary and up to half of patients may require further treatment within 5 years. SLT is an effective supplement or alternative to drops for the treatment of glaucoma.
Laser Peripheral Iridotomy is a procedure to prevent angle closure glaucoma. By creating an opening in the iris, fluid pressure between the front and back of the eye equalizes. This avoids forward bowing of the iris and potential closure of the angle.
Surgical Treatment
In cases where drops or laser is inadequate in controlling the eye pressure, surgery is required.
Endoscopic Cyclophotocoagulation (ECP) is a surgical procedure where laser is used to coagulate or destroy the ciliary processes. The ciliary processes produce fluid which circulates through the eye. By reducing the number of ciliary processes, eye pressure should decrease. Under local anesthesia, a fiberoptic viewing system and laser probe are used to visualize and treat the ciliary processes.
Shunting Procedures re-direct aqueous out of the eye, therefore lowering eye pressure. There are several types of glaucoma shunting procedures. Trabeculectomy Surgery is the creation of a partial thickness opening in the eye. This allows aqueous to slowly filter out of the eye, lowering the pressure. Another shunting procedure involves the suturing of Drainage Valve Implants next to the eye. A reservoir is connected to a tube which is inserted into the eye, allowing drainage of aqueous, lowering eye pressure. Recent evidence suggests drainage implants have a higher success rate and less complications than other glaucoma surgeries.