Selective Laser Trabeculoplasty

Selective laser trabeculoplasty (SLT) is a laser surgical procedure used to help lower intraocular pressure (IOP) of patients with open-angle glaucoma. SLT is used to treat the eye’s drainage system, known as the trabecular meshwork—the mesh-like drainage canals that surround the iris. Treating this area of the eye’s natural drainage system improves the flow of fluid out of the eye, helping to lower the pressure.

The laser used in SLT works at very low levels. It treats specific cells selectively, leaving untreated portions of the trabecular meshwork intact. For this reason, SLT, unlike other types of laser surgery, may be safely repeated many times.

SLT is typically performed in the ophthalmologist’s (Eye M.D.’s) office or an outpatient surgery center. The procedure usually takes about five to ten minutes. First, anesthetic drops are placed in your eye. The laser machine looks similar to the examination microscope that your ophthalmologist uses to look at your eyes at each office visit.

You will experience a flash of light with each laser application. Most people are comfortable and do not experience any significant pain during the surgery, although some may feel a little pressure in the eye during the procedure.

Most people will need to have their pressure checked after the laser treatment, since there is a risk of increasing IOP after the procedure. If this does occur, you may require medications to lower the pressure, which will be administered in the office. Rarely, the pressure in the eye increases to a high level and does not come down. If this happens, you may require a surgery in the operating room to lower the pressure.

Most people notice some blurring of their vision after the laser treatment. This typically clears within a few hours. The chance of your vision becoming permanently affected from this laser procedure is very small.

Most patients can resume normal daily activities the day after laser surgery. You may need to use eye drops after the procedure to help the eye heal properly.

Risks associated with SLT include:

• increased pressure in the eye, possibly requiring medication or surgery;
• inflammation in the eye;
• bleeding;
• damage to the cornea, iris, or retina from the laser light;
• failure to adequately lower the eye pressure; and
• need for repeat laser surgery.

It will take several weeks to determine how much the SLT will lower your eye pressure. You may require additional drops, laser or glaucoma incisional surgery to lower the pressure if it is not sufficiently lower after the first laser treatment.

One landmark glaucoma study in 2019 demonstrated compelling evidence that SLT is an effective first-like therapy for open angle forms of glaucoma, and may be superior to eye drop treatment as initial therapy. However, it can also be offered for patients already taking eye drops. Some patients may be able to eliminate an eye drop after the laser, but for those already taking eye drops and needing additional intervention, often times they need the effect of both the eye drops and the SLT treatment to lower the eye pressure to target level.

While some people may experience side effects from medications or surgery, the risks associated with these side effects should be balanced against the greater risk of leaving glaucoma untreated and losing your vision.

Transscleral Cyclophotocoagulation (CPC)

Laser cyclophotocoagulation is a laser treatment used to decrease pressure inside the eye. This laser technology utilizes a diode laser (wavelength of 810 nm) to alter the fluid-forming cells in the ciliary body (a structure located behind the iris) so they produce less aqueous humor. The procedure itself takes no more than three minutes but is done in the operating room simply for the patient’s comfort. A small volume of anesthetic is injected around the eye for pain control and an anesthesiologist also administers anesthetic intravenously. The laser procedure itself simply involves the contact of a probe with the surface of the eye near the junction of the sclera (white shell of the eyeball) and the cornea (clear front part of the eye). The laser energy is delivered through the sclera (transscleral-ly) and thus there are no incisions into the eyeball itself. You may have mild pain in the immediate hours following the procedure which typically resolves with tylenol. You will have a patch over the eye due to the injection around the eye which can result in double vision or blurry vision until this anesthetic wears off. You will not have any activity restrictions following this laser other than the recommendation not to drive for 24 hours due to the anesthesia you have received.

There are two forms of this laser: traditional CPC and micropulse CPC.

Traditional CPC

This version of the laser is much more powerful than its ‘baby cousin,’ the micropulse version. It has greater capacity to reduce eye pressure, but at the cost of causing a great deal of inflammation, as the ciliary bodies are literally destroyed. For this reason, the traditional CPC laser is reserved for eyes with very limited or poor visual potential (‘counting fingers’ or worse), or in some instances for patients who do not desire or are not candidates for incisional glaucoma surgery. There is an exceedingly rare but documented risk of vision loss in the fellow eye with this procedure due to an inflammatory problem called sympathetic ophthalmia.

Micropulse CPC

MicroPulse® cyclophotocoagulation laser therapy is a much gentler version of the CPC laser and can be performed in the treatment of all stages of glaucoma. With MicroPulse® cyclophotocoagulation laser therapy, a continuous-wave laser beam is chopped into a train of short, repetitive, low energy pulses separated by a brief rest period which allows the tissue to cool between laser pulses. It therefore can be performed in ‘well-seeing’ eyes without concern of inciting a large amount of inflammation. The mechanism of this laser is still debated, but there are thoughts that it may work on both the inflow and outflow pathways to reduce eye pressure. This laser can be performed multiple times on the same eye.

Laser Iridotomy

This procedure is done in the setting of anatomical narrow angles that are found to be occludable, which simply means the angle formed in your eye between the cornea (clear front part of eye) and iris (colored part of eye), where the internal drainage pathway sits, is narrow to the threshold of being at risk for becoming suddenly blocked off. If this sudden blockage were to take place, which is referred to as acute angle closure glaucoma, the pressure in your eye would rise very high very suddenly, and as a result you would develop severe pain in the eye, a decline in vision, and possibly see halos around lights and experience nausea or vomiting. If your doctor feels that you have reached the threshold of needing intervention, it is considered unsafe to dilate your eyes until after the laser procedure is performed. You should also be aware that certain medications that have the ability to dilate the pupil can put you at risk for acute angle closure glaucoma. The most common culprits over the counter are allergy medications, cough suppressants, and nausea medications. Commonly prescribed medications that have the ability to induce an attack include medications used to treat depression or anxiety, among many others. If you have been taking one of these medications for years and have not had a problem, it is impossible for your doctor to give you the percent likelihood that one of these drugs will precipitate an attack in your eye, (s)he can only simply inform you that the risk is there.

If your eyes are deemed to have occludable angles, a laser iridotomy will be recommended for you. This is a relatively quick procedure that is done in the clinic setting, and works by creating a tiny little hole in the iris (colored part of the eye) which works to create an alternative route for fluid to prevent a sudden pressure spike in your eye. This prevents the sudden, or acute, form of angle closure glaucoma and may not prevent a more chronic form of angle closure glaucoma which can happen slowly and insidiously over time of the iris scars into the drainage pathway.

For the procedure itself, your doctor will hold a lens on your eye after it has been numbed. You will sit at a microscope similar to the ones your doctor uses to examine your eyes. The procedure should not be excruciatingly painful, however, it is not the most comfortable experience. Most patients describe something like a light rubber band snap to the eye with each energy application, which is fractions of a second. The number of energy applications depend on how thick your iris is, but typically the procedure does not take more than a few minutes. You will use a steroid drop for several days following the procedure and will not have any activity restrictions.

The benefits of the procedure far outweigh the risks, but the risks include bleeding, a corneal scratch or infection, a retinal tear or detachment, prolonged inflammation, or a small shadow in the area of the laser opening, among many even less common risks.