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
Open Angle Glaucoma 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 occurs when the drainage angle becomes closed. Eye pressure rapidly and severely elevates and causes severe pain and vision loss. Acute angle closure glaucoma is an emergency.
Neovascular Glaucoma is caused by abnormal blood vessels growing over the iris and angle. This causes progressive angle closure, pain and vision loss. Prompt treatment, with intravitreal medication, laser treatment, and sometimes surgery is necessary to treat the condition.
Eye pressure is measured at each visit. Careful examination of the eye for conditions contributing to glaucoma is performed. Testing, when indicated, is done to measure glaucoma damage.
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
In Angle Closure or Neovascular Glaucoma, underlying eye problems can be addressed to prevent glaucoma. For Open Angle Glaucoma, lowering the eye pressure is the only known way of preventing loss of vision from glaucoma.
Topical medications (drops) are the mainstay of glaucoma therapy. These medications work either by decreasing aqueous production, or increasing aqueous outflow.
Medications that reduce aqueous production:
Beta Blockers (Timoptic and Betopic)
Alpha Agonists (Alphagan)
Carbonic Anhydrase Inhibitors (Trusopt, Azopt, Diamox)
Medications that increase aqueous drainage:
Prostaglandins (Xalatan, Lumigan, Travatan)
Miotic agents (Pilocarpine)
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 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 equalize. This avoids forward bowing of the iris and potential closure of the angle.
In cases where drops or laser is inadequate in controlling the eye pressure, surgery is required. In glaucoma surgery aqueous within the eye is shunted or re-directed out of the eye, therefore lowering eye pressure. There are several types of glaucoma shunting procedures:
Drainage Valve Implants are sutured next to the eye. They are 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.
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.