As a first-line treatment for glaucoma, medications have many disadvantages. Glaucoma patients are forced to tolerate drug side effects and ongoing medical expenses, and the effectiveness of the treatment may be undercut because patients are often non-compliant. Yet until now, alternative treatment options have had enough drawbacks that most doctors haven't chosen them as their first-line glaucoma treatment.

That may soon change. An ever-increasing number of studies suggest that Selective Laser Trabeculotherapy (SLT) is a safe and effective treatment for most glaucoma patients -- so safe that it could eventually replace medication as most doctors' first choice for treatment.

Selective Laser Trabeculotherapy offers the benefits of argon laser trabeculoplasty (ALT), without the irreversible damage that ALT causes. SLT uses a q-switched, 532-nm Nd:YAG laser (Coherent's Selecta 7000) to irradiate the trabecular meshwork (TM). This triggers a biological response that causes increased outflow.

SLT has several noteworthy characteristics:

• It's selective.
Because of the specific wavelength of light generated, as well as the power and duration of the exposure, SLT selectively targets pigmented cells in the trabecular meshwork and causes no discernable damage to adjacent tissue. Researchers have found treated and untreated tissue to be nearly indistinguishable (see photos, below).
• It's non-thermal.
The intracellular microdisruption triggered by the laser is confined to the targeted cells. This is because the laser activates specific biological mechanisms, rather than coagulating or ablating tissue. Also, the laser pulse is so short that heat caused within the targeted cells doesn't have time to spread to surrounding tissue.
• It's repeatable.
If the initial treatment fails to lower IOP sufficiently, further treatments may still be effective. At the same time, studies have found that multiple treatments with SLT cause no damage to the TM. (In contrast, repeated treatments using ALT can lead to scarring of the TM, elevation of IOP and the creation of open-angle glaucoma.)
• It's effective for patients who've had prior treatment with ALT.
Numerous studies have shown that SLT can be used safely on patients who've been treated with ALT. And results have been just as good for these patients as for those who had not received prior treatment with ALT.

The mechanisms that allow SLT and ALT to lower IOP appear to be different -- at least in part. For example, the thermal damage resulting from ALT causes tissue contraction, which results in the widening of passages for aqueous outflow. SLT doesn't have this effect.

However, both treatments appear to attract macrophages to the treated tissue by triggering the release of cytokines. The macrophages engulf melanin granules and clear them from the TM tissues when they flow out of the eye and return to circulation via Schlemm's canal. (Research performed by Jorge Alvarado, M.D., et al has shown that introducing macrophages into the anterior chamber of enucleated human and experimental eyes causes a rapid and lasting increase in outflow.)

The selective targeting of melanocytes also acts to increase outflow by causing selective cytolysis and cellular proliferation, which invigorates TM filtering and outflow.

SLT is available outside the U.S., and it's been in full clinical use in Japan and Europe for more than 2 years. As a result, a large number of studies of SLT have been conducted in countries around the world, including Japan, Germany, France, Norway, Mexico, Italy, Korea and the U.S. Results have consistently shown that 70% of patients or more respond to SLT with 20% to 39% drops in IOP. Results have been stable when checked as long as 3 years after the procedure.

Complications have been minimal. A study of 460 eyes conducted by Peter Kaulern, M.D., Ph.D., in Germany, found the complication rate for SLT to be 4.5%. (ALT complication rates have been reported as high as 34%, which may not be surprising given the tissue damage caused by ALT.)

SLT complications in the Kaulern study included:

• 11 eyes had a pressure spike in the second postoperative week; two of these were accompanied by an inflammatory reaction of the anterior chamber.
• Seven eyes had an inflammatory response, but no IOP pressure spike.

Dr. Kaulern noted that all complications were easily treated with topical steroids. Other complications, such as tissue traumatization, did not occur. Miotics, which these researchers normally apply following ALT, were not necessary after SLT.

Mark A. Latina, M.D., (originator of SLT) also points out that one of the most notable differences between ALT and SLT is the absence of peripheral anterior synechia formation
following SLT.

FDA approval for SLT in the U.S. still hasn't been granted, despite SLT's use of existing technology and considerable evidence that the procedure is effective and safe. Hopefully, approval will come in the near future.

Because SLT lowers IOP without the side effects and lack of compliance associated with drug therapies -- and because there's no evidence that it causes damage -- it could indeed turn out to be an ideal first-line treatment for glaucoma. And that would be good news for millions of glaucoma patients.