During laser treatment for open-angle glaucoma, laser light is aimed at the eye’s trabecular meshwork (the eye’s drainage system). The laser application results in a biological and mechanical reaction in the trabecular meshwork to open the previously blocked meshwork and increases the flow of aqueous fluid from the eye.

The most common conventional (incision) surgical technique is called filtering microsurgery, which involves making a hole through which the excess fluid drains and lowers pressure in the eye. Surgery is used if medication and laser procedures have not been successful or if there is a medical emergency for which pressure must be relieved immediately.

Laser Surgery
Laser surgeries lower intraocular pressure by enhancing the drainage of aqueous fluid or slowing its production. The kind of laser surgery used depends on the type of glaucoma being treated. The length of time the pressure remains lowered depends on the type of laser surgery, the type of glaucoma, and the patient’s individual characteristics.

In some cases, laser surgery may have to be repeated to control internal eye pressure more effectively. Typically, medications will still be needed to maintain fluid pressure within the eye, although a lower dose than previously used may be sufficient. If the laser therapy does not lower the pressure in the eye satisfactorily or the effects wear off, the surgeon may recommend conventional surgery.

What to expect: Laser surgeries are preformed in a doctor’s office in a facility called an ambulatory surgical center or in a hospital. Although some patients may experience a slight stinging sensation, the procedures are usually painless. In some instances, local anesthetic agents are used, in which case there is little if any discomfort.

When the procedure is over, patients may experience blurred vision and some irritation. Normal activities, such as driving and work, may be resumed the next day.

Risks: As with all surgery, there are risks. Risks of laser glaucoma procedures may include a short-term increase in intraocular pressure or an excessive drop in pressure. Both complications are rare and controlled with glaucoma medications. There is a small risk for cataract formation after some types of surgery.

Benefits: Failure to control glaucoma can result in destruction of the optic nerve and permanent blindness of the affected eye. Reducing or preventing raised intraocular pressure by laser therapy is effective in reducing the risk of blindness from glaucoma.

Laser Treatments for Primary Open-Angle Glaucoma

• Selective laser trabeculoplasty (SLT) reduces intraocular pressure by enhancing drainage of excess aqueous fluid. The laser increases drainage by selectively treating certain cell tissue of the trabecular meshwork. The meshwork is at the entrance of the drainage canals. SLT treatments can occasionally be repeated if necessary.
• Argon laser trabeculoplasty (ALT) reduces intraocular pressure by opening the drainage canals of the eye. In many cases, drugs will continue to be needed to maintain safe internal eye pressure after this procedure.

Laser Treatments for Narrow-Angle Glaucoma

• Laser peripheral iridotomy (LPI) reduces excessive intraocular pressure by making a small hole in the iris, the colored part of the eye. Narrow-angle glaucoma occurs when the angle between the iris and cornea, the clear front part of the eye, is too small. The hole allows the iris to move back from the cornea, opening the angle and enhancing aqueous flow.
• Laser cyclophotocoagulation is used to reduce eye pressure by treating the ciliary body, which produces aqueous fluid. The procedure is most commonly used for patients with extensive and end stage glaucoma damage that are not responding to other glaucoma surgeries.

Conventional or Incision Surgery
As noted above, conventional surgery or filtering microsurgery is used when management of glaucoma through medication and laser surgery has failed or is less desirable. Trabeculectomy is most commonly used to prevent or curtail damage to the optic nerve by reducing intraocular pressure. In this procedure, a small incision is made in the sclera of the eye (see Diagram 2) and a flap of tissue is left to cover the incision, allowing slow release of fluid from the inside the eye to its outer layers. The procedure results in the formation of a small blister-like bump called a “bleb.” The bleb is covered by the eyelid and is usually not visible. The excess fluid is carried away as it is absorbed into the bloodstream.

Diagram 2

Illustration courtesy National Eye Institute

A new modification of trabeculectomy, is non-penetrating deep sclerectomy or viscocanalostomy, where a full-thickness hole in the eye is avoided. Instead, a very deep dissection is performed in the sclera and trabecular meshwork. Intraocular pressure is lowered as fluid oozes through a permeable thin layer of tissue that is created by the viscocanalostomy. A bleb may be formed, but it is usually smaller than one that would be formed following trabeculectomy.

In case of complicated glaucoma or patients who have had multiple surgeries, the use of a tube-shunt or seton is required. These devices, which include the Ahmed Valve, Baervedlt device, or Molteno device, have a plastic tube that is placed in the eye, which drains to an external reservoir placed outside the eye.

What to expect: Microsurgical procedures are performed in an ambulatory surgical center or on an outpatient basis at a hospital. Patients are usually given limited intravenous sedation but may be given general anesthesia. Medication may also be administered around the eye to prevent its movement. Typically, patients are relaxed and experience little if any discomfort.

Risks and benefits: The risks of incision surgery are small. Nevertheless, as with any incision, there is the risk of bleeding and infection. The eye may be red or inflamed, with discomfort and pain. In some instances, the procedure may not reduce eye pressure as intended. Loss of too much pressure can result in a loss of vision. As with laser surgeries, there are occasional instances in which the pressure is too high or too low. When this occurs, medications or additional surgeries may be needed to control the condition. In some instances, cataracts may develop. In very rare circumstances, an eye can be removed as a result of surgery. As with all procedures or medications, the risks need to be balanced with the benefits of saving vision in the affected eye. Failure to control glaucoma can result in destruction of the optic nerve and permanent blindness in the affected eye.

Success rates for glaucoma filtering surgery are about 70% to 90% for at least 1 year. In some instances, the surgically created drainage channel may “heal” or close, in which case high intraocular pressure can recur. The healing or closure of the drainage opening is a natural process that is more likely to develop in younger people. To prevent or retard closure, drugs such as mitomycin-C and 5-fluorouracil may be administered. If necessary, the surgery can be repeated in the same eye.

Glaucoma surgery takes place on an outpatient basis. Patients are sedated during the procedure and return home later in the day. (Photo courtesy Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD)