There are many kinds of glaucoma. We classify the type of glaucoma according to the reason for the blockage in the outflow of fluid. The following two are by far the most common, and the main types of glaucoma treated with laser surgery.
Angle Closure Glaucoma
This type of glaucoma, which accounts for 10% of all glaucomas in the U.S., occurs when the angle between the cornea (the clear window into the eye) and the iris (the colored portion of the eye) is narrow. In all eyes, ocular fluid meets resistance passing from the posterior chamber behind the iris to the anterior chamber in front of the iris. This resistance to the forward flow of fluid causes a slightly increased fluid pressure behind the iris that pushes the iris forward. In eyes with narrow angles, there is not enough room between the iris and the drain of the eye. The forward bowing of the iris from the pressure behind it blocks the drain and thus raises the intraocular pressure. A laser beam is used to make a small hole in the iris called an iridectomy, which allows the fluid to flow from the back to the front of the iris without resistance. Eliminating the higher pressure behind the iris allows it to move back away from the drain. Some irises, especially those that are dark brown, are thicker than others and may require more than one procedure to secure a permanent opening. On the first postoperative visit when the iridectomy is examined for blockage or healing, it is possible to tell whether further laser is needed.
The laser procedure takes only a short time and is surprisingly painless. The patient feels the impact of the laser as a light tap on the eye. This impact is startling but not painful. After completing the surgery, most patients wonder why they worried the night before.
If an iridectomy is accomplished before any blockage of the drain with iris takes place, the patient is usually cured of this form of glaucoma. Occasionally, a high roll in the iris will keep the iris dangerously close to the drain and medication or another laser procedure called a gonioplasty will be needed. Since other types of glaucoma besides angle closure glaucoma may still occur later in life, periodic eye exams continue to be necessary.
Chronic Open Angle Glaucoma
This is the most common form of glaucoma. One in ten elderly blacks and one in fifty elderly whites have open angle glaucoma. It is uncommon in whites before the age of fifty and in blacks before forty.
In eyes with normal fluid outflow, the fluid leaves the eye through a fine, sieve-like structure called the trabecular meshwork before entering a canal which carries the fluid into veins outside the eye. In open-angle glaucoma, this sieve-like structure becomes blocked by deposits that are a consequence of abnormal aging changes within the eye. Increasing blockage gradually causes the pressure to rise slowly over a long period of time, causing damage the optic nerve.
Since there are no symptoms to bring the patient to the doctor, severe damage to the optic nerve may occur before the patient realizes anything is wrong. Damage to the optic nerve will eventually show up on visual field testing as areas of decreased visual perception. Because the majority of glaucoma damage occurs before the patient sees the doctor, regular visits to the eye doctor allow glaucoma to be discovered at an early stage. In most cases, eye pressure can be adequately controlled with medication. When medication no longer keeps the pressure low enough to prevent further optic nerve damage, laser therapy is considered. We have found laser surgery in appropriate patients to lower intraocular pressure an average of 25 to 35%, with the greatest lowering of pressure being approximately 4-6 weeks after laser surgery. Patients who respond the best are over 60 years of age, have a brown color in their drain that allows the light of the laser to be absorbed, and have as their diagnosis either primary open angle glaucoma, normal-tension glaucoma, pseudoexfoliative glaucoma, or pigmentary glaucoma.
Laser surgery for open-angle glaucoma is called a trabeculoplasty, and involves making microscopic burns in the trabecular meshwork. One theory as to why this treatment works is that when the laser beam hits an area of tissue, that tissue shrinks. This, in turn, pulls open the holes in the drain immediately surrounding the burns, allowing more fluid to leave the eye. Another theory is that the injury of the laser burn itself stimulates cells in the trabecular meshwork to clean up accumulated debris that has been blocking the drain.
Laser surgery is not a cure for open angle glaucoma. It should be thought of as adding another strong medication to the medications the patient is already taking. Occasionally, one or more of the drops that the patient has been taking can be stopped after a trabeculoplasty, but this is not usual. If the laser surgery is effective, the amount of intraocular pressure lowering slowly diminishes over time. Little effect remains in most patients after three to five years. In patients who had a fairly long-lasting effect from their original trabeculoplasty, the procedure can be repeated once. However, the drop in intraocular pressure the second time will not be as great as was initially seen.
What Happens After Laser Surgery?
Immediately following the procedure, drops are used to lessen inflammation and lower eye pressure. The patient is asked to wait for approximately one hour after the laser so that the eye can be checked for any side effects. It is usual for the vision to be slightly blurred and the eye somewhat irritated for a day after the procedure. Since the eye is not opened with the laser procedures discussed here, there is no need to limit any postoperative activities. Postoperatively, patients are asked to continue their regular glaucoma medications and to start an additional drop to prevent inflammation. This new drop should be taken four times a day for five to seven days. It may be taken along with the glaucoma drops as long as ten minutes are allowed between any two drops. A follow-up visit is scheduled approximately a week after the laser surgery.
All instructions need to be followed carefully for best results. If you have any questions after reading this, please ask your doctor.