SUCCESSFUL SLT

Selective laser trabeculoplasty (SLT) is an attractive option for lowering intraocular pressure (IOP) because it is at least as effective as argon laser trabeculoplasty but causes less coagulative damage to the trabecular meshwork (TM). However, SLT can have its challenges, Hady Saheb MD, MPH, FRCSC told Glaucoma Day 2014 at the American Society of Cataract and Refractive Surgery annual meeting in Boston.

Along with his own SLT settings, Dr Saheb of McGill University offered five pearls for avoiding some of the more common problems he encounters with SLT.

Dr Saheb’s settings

Currently, Dr Saheb uses pilocarpine 1-2 per cent and Iopidine preoperatively to prevent IOP spikes. He uses a Latina SLT gonio lens to visualise the angle during the procedure. He applies three nanosecond 400 micron bursts centred on the TM, but notes this spot size overlaps the TM both anteriorly and posteriorly. He starts at 0.7 mJ and titrates power up, adjusting two to three times during the procedure as outlined below. He usually delivers 70 to 90 shots over 360 degrees, rotating the lens in the opposite direction as the laser.

Postoperatively, Dr Saheb checks IOP at one hour, and two months after surgery. He recommends a closer follow-up at one week for patients with an IOP spike at the one-hour check, and those with a history of uveitis, advanced glaucoma, pigment dispersion glaucoma or highly pigmented TM, who also usually have pseudoexfoliation glaucoma. He does not routinely use steroids, but has a low threshold for prescribing them as mentioned below.

1. Choose the right patient

Dr Saheb noted that the goal of SLT shares some similarities with that of microinvasive glaucoma surgery – moderately reducing IOP by improving the physiologic outflow pathway. So he applies similar criteria, considering SLT for patients with ocular hypertension, primary open-angle glaucoma, pseudoexfoliation and pigment dispersion glaucoma.

Dr Saheb avoids patients with very uncontrolled IOP. “What you are doing with SLT is optimising trabecular outflow. So if someone has very diseased trabecular outflow, such as with severely uncontrolled glaucoma, SLT is not a good option.” Likewise, he avoids post-filtration surgery patients and those with normal tension glaucoma because their very low IOP targets cannot be met by adjusting trabecular outflow.

2. Don’t get drunk

“Champagne bubbles” are a sign that adequate treatment power has been reached, but seeing them with every burn means you’re using too much power, Dr Saheb said. He recommends titrating to see bubbles every second or third burn, and adjusting power two or three times as TM pigmentation varies over 360 degrees.

3. Get a good look

An unobstructed view aids accuracy. Dr Saheb recommends moving the gonio lens toward the target to better visualise narrow angles, turning down the light to reduce light scatter from hazy corneas, and cleaning or moving the gonio lens as needed to reduce excess reflections. For patients with brows that extend well anterior of the eye surface, he suggests asking the patient to tilt their head back slightly. “Access of the gonio lens is so much easier when the head is at an angle in these patients.”

4. Easy with the PDG

Pigment dispersion glaucoma (PDG) patients are particularly prone to IOP spikes, so Dr Saheb goes easy with them. He starts with a test dose as low as 0.3 mJ, and checks IOP after 10 spots. If the test is successful, he treats one-quarter of the TM at a time and checks IOP after each. He also follows these patients closely after laser.

5. Don’t sweat the steroids

It’s theorised that SLT’s mechanism of action involves an inflammatory response that helps clear the TM. Therefore, steroids should not be used as they might counteract this effect. However, this theory has not been substantiated, and unpublished randomised trials reported to Dr Saheb by research colleagues found no difference in efficacy with or without postoperative steroids.

Even so, Dr Saheb does not routinely prescribe steroids. But if there is pain in the first eye or if a patient in for retreatment had pain the first time, he does not hesitate.

Following these tips can help improve SLT outcomes, Dr Saheb said.

Hady Saheb: hady.saheb@mcgill.ca