Although a person can develop glaucoma at any pressure, studies have proven that regardless of the starting eye pressure, lowering the eye pressure further can slow down or stop the progression of glaucoma. How much the pressure needs to be lowered is individual and depends on the maximal untreated eye pressure, the amount of damage to the optic nerve and the amount of visual field loss present.
Before discussing treatment, it is important to briefly discuss fluid dynamics in the eye. The eye constantly makes a fluid called aqueous humor. This fluid brings oxygen and nutrients to structures in the eye that have no direct blood supply. Aqueous travels around the lens, through the pupil, and leaves through the trabecular meshwork.
The difference between the amount of fluid being made and the amount draining from the eye determines the eye pressure.
There are many ways to lower eye pressure. The first line of therapy is eye drops. Some lower pressure by decreasing the amount of fluid made in the eye, while others improve outflow. They can be used in combination to maximize pressure lowering. Most of these drops have few systemic side effects, but can cause some eye irritation, redness or itching.
There are several different lasers available for the treatment of glaucoma. Some are only appropriate for certain types of glaucoma. The most common laser procedures are laser peripheral iridotomy, laser trabeculoplasty and transscleral cyclophotocoagulation.
Laser peripheral iritomy (LPI)
This is a procedure used specifically for angle closure glaucoma or narrow angle glaucoma. In these types of glaucoma, fluid has a difficult time getting through the pupil to the front part of the eye. As a result, pressure builds up behind the iris and bows it forward like the sail of a sailboat. In general, this is a gradual process and causes narrowing of the angle which your doctor can see by gonioscopy. As the iris continues to bow forward, it can eventually block the drain and cause an attack of glaucoma.
A laser peripheral iridotomy is a small hole in the iris that allows the fluid to bypass the pupil and get to the front of the eye. As the pressure in front of and behind the iris equalizes, the iris will flatten and the drain will open. It is performed in the office using a contact lens. This procedure can be used to break an acute attack of glaucoma. More commonly, it is used as a prophylactic measure in eyes with progressively narrowing angles that are at risk for angle closure. It will not work if the iris has already scarred to the trabecular meshwork.
If eye drops do not adequately lower the eye pressure, a treatment called "laser trabeculoplasty" can be performed to improve fluid outflow. You must have an open angle to be a candidate for this procedure. It is performed in-office and takes about 10 minutes to complete. The eye is numbed with a topical anesthetic drop and a contact lens is placed on the eye to visualize the trabecular meshwork. Laser is then applied to the trabecular meshwork for 180 to 360 degrees. It takes about 4 weeks for laser treatment to achieve maximal benefit.
This treatment has a 70% success rate in lowering pressure, and is particularly effective in pigmentary and pseudoexfoliation glaucoma. However, over time the effect can wear off.
This is a procedure generally used for refractory glaucoma. We use a laser to treat the ciliary body, the part of the eye that makes fluid. In essence, we are damaging this area so it makes less fluid over time. While this laser can effectively lower pressure, it is less predictable than surgical procedures. A person may require more than one treatment to achieve the desired pressure. There is also a small risk of low eye pressure and decreased vision after the procedure. For these reasons, this laser is usually considered after surgery has failed or in eyes with poor vision that are unlikely to see better in the future.
The advantage of this procedure is that it is non-invasive. It is performed in the clinic after the eye is numbed with an injection. The laser is applied through the white part of the eye and the eye is patched for 8 hours. It takes about 1 month to reach maximal effect, and so all glaucoma medications are continued during this time.
The most commonly performed surgery is trabeculectomy. This filtering surgery is the equivalent of a bypass procedure, allowing the fluid to exit the eye without passing through the trabecular meshwork. A trabeculectomy surgery is performed in the operating room under local anesthesia.
A trap door is made in the sclera under the upper eyelid. Fluid can seep out through the trap door, under the conjunctiva and then be absorbed by the body. This collection of fluid is called a bleb.
First-time trabeculectomy surgery is 80-85% successful. The main reason for failure is excessive scarring around the filtering site. While medications are used during and after surgery to prevent scarring, sometimes they are unsuccessful. In these cases, a revision of the surgery or another surgery may be necessary.
Tube shunts are implant devices through which fluid can exit the eye. They consist of a tube that is placed in the anterior chamber, connected to a plate placed on the outside of the eye. Fluid flows through the tube and over the plate before being reabsorbed by the body.
A successful trabeculectomy tends to get lower pressures than a tube. However, in certain types of glaucoma, such as uveitic glaucoma and neovascular glaucoma, tubes may be more successful than a trabeculectomy. Similar to trabeculectomy, the final pressure after a tube is placed will depend of the amount of scar tissue that forms around the plate.