Predictors of Failure After Laser Surgery for Glaucoma

Barbara Boughton

March 25, 2013

SAN FRANCISCO, California — Laser trabeculoplasty procedures can fail in 30% to 40% of patients with glaucoma, and they will need additional treatment to control their eye disease, according to 2 new studies.

Although some experts question whether the failure rate for laser procedures is truly that high, the studies presented here at the American Glaucoma Society 23rd Annual Meeting suggest that laser therapies don't work for everyone and that treatment should be individualized to each patient.

"In our study of argon laser trabeculoplasty, we found that myopic patients had better outcomes," said researcher Eric Chang, from the University of Texas Southwestern Medical Center in Dallas.

In their retrospective study, Chang and his team examined 206 patients with glaucoma who underwent argon laser trabeculoplasty, performed by residents, at a Veterans Administration Hospital in Dallas from 2001 to 2011.

They analyzed patient characteristics, such as intraocular pressure, visual field defects, family history of glaucoma, refractive error, hypertension, diabetes, central corneal thickness, number of preoperative medications, and the laser energy used during the procedure, to determine predictors of failure.

Of the procedures, 40.8% were classified as failures.

The researchers found a higher risk for failure associated with a family history of glaucoma, higher intraocular pressure, and laser energy used during the procedure. A lower risk for failure was associated with the use of a greater number of glaucoma medications before surgery, he reported.

At a median follow-up of 2 years, the argon laser procedure was considered to be a failure if the patient received additional treatments, such as laser therapy, glaucoma-filtering surgery, or glaucoma medications.

The researchers found that myopia was protective against failure (odds ratio [OR], 0.39; = .005)

"We also found that the less energy used for argon laser trabeculoplasty, the better the results [OR for a 20 K increase in energy,1.6; P = .005]. We think the reason may involve trabecular meshwork scarring," Chang said.

In addition, the use of more than 3 glaucoma medications prior to the procedure was associated with a reduced failure rate, he noted.

In the second retrospective study, the researchers examined 189 patients with primary open-angle glaucoma who underwent selective laser trabeculoplasty, performed by full-time faculty, at the University Eye Clinic in Dallas from 2001 to 2011.

After a median follow-up of 2 years, 29.6% of the procedures were classified as failures. As in the first study, failure was defined as the need for additional laser trabeculoplasty, glaucoma-filtering surgery, or glaucoma medications.

High Failure Rate

The results, presented by Nathan Markel, also from the University of Texas Southwestern Medical Center, show a higher risk for failure after selective laser trabeculoplasty if there is a family history of glaucoma (OR, 1.7; P = .02), a higher preoperative intraocular pressure (OR, 1.1; = .03), and moderate to severe visual field defects (OR, 2.6; = .006).

Markel and colleagues conclude that clinicians should perform selective laser trabeculoplasty when intraocular pressure is lower and visual field defects are less severe.

"Although selective laser trabeculoplasty is a relatively routine procedure, it doesn't always work, and when it does, it doesn't last forever," said Andrew Iwach, MD, a spokesperson for the American Academy of Ophthalmology and executive director of the Glaucoma Center of San Francisco in California.

"If you have a patient with very high pressure or a very damaged optic nerve, laser treatment may not be enough," Dr. Iwach told Medscape Medical News. "We need to look at different treatment options...and customize the therapy to the patient."

The selective laser procedure study is interesting because it looks at treatment from a clinical management perspective, rather than how much intraocular pressure dropped afterward. "It tells us how effective selective laser trabeculoplasty was in delaying another step in treatment," Dr. Iwach said.

These 2 studies contain some intriguing results, such as the finding that patients with myopia did better after the argon laser procedure, but both have several limitations, said Anne Coleman, MD, from the University of California at Los Angeles.

In retrospective trials where subjects are not randomized, outcomes can be influenced by the management of individual clinicians, Dr. Coleman told Medscape Medical News.

Advanced statistical methods can help control for the influence of management by different clinicians, but no such methods were used in these studies, she noted. Also, the reasons for success were different in the 2 studies, indicating that more research is needed in this area, she said.

Dr. Coleman pointed out that most studies show that laser trabeculoplasty works in about 80% of patients. However, in these studies, the success rate was about 60% to 66% after 2 years of follow-up — an unusually high failure rate.

The recommendation that "clinicians may want to use selective laser trabeculoplasty earlier when the pressures are lower and damage is mild to moderate" should be interpreted with caution, she said.

Mr. Chang, Mr. Markel, and Dr. Coleman have disclosed no relevant financial relationships. Dr. Iwach reports being a speaker for Lumenis and Ellex Laser Systems and a consultant for IRIDEX.

American Glaucoma Society (AGS) 23rd Annual Meeting: Abstracts 76 and 78. Presented March 2, 2013.

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