Guest Editorial

General guidelines for STL

By Sam Mansour, MD

Over the past few years, refinements made to laser delivery devices have yielded more tissue-sparing (subthreshold) modes. Four laser manufacturers — Iridex Corp.; Quantel Medical (MicroPulse); Topcon (Endpoint Management); Navilas Microsecond Pulsing (OD-OS); and Ellex (2RT) — have designed subthreshold laser (STL) systems that can be safely applied over the fovea without causing visible damage. But there are caveats.

Clinicians who wish to use this popular adjunctive treatment need to follow a safe and sound protocol for applying it, particularly if it involves transfoveal application. The retina of some patients, such as those with metabolically compromised RPE cells due to systemic disease or who have had certain chronic drug exposure, may not react as expected as less compromised cells in terms of response to laser, pharmacotherapy or other interventions.

The following steps are based on personal experience with the Iridex MicroPulse IQ 577 laser system. It is vital, however, that all users of STL therapy adopt similar guidelines — to be used on all patients —for their particular system.

Initially, perform a continuous-wave (CW) test spot with a spot size (Adapter) of 200 μm using the Mainster Focal Grid/equivalent (Magnification ≤ 1.1x) lens, pulse duration of 200 ms and power of 50mW. Apply this test spot to the non-edematous macula > 2 dd from foveal center, titrating power upwards by 10 mW increments (moving to a new area each time) until a barely visible tissue reaction is seen. If a reaction is evident with 50 mW, the power needn’t be increased. After obtaining the final threshold power, switch the laser to 5 percent duty cycle and adjust the power to four times the test-spot threshold to perform the initial session. The remainder of the settings including spot size, lens and duration remain the same as in the test spot mode. If using the multi-spot TxCell scanning delivery system, ensure that there is confluent treatment using 0.00 spot or 0.25 spacing within the patterned grid. If using single-spot delivery, ensure high-density delivery. I tend to minimize treatment overlap and treat all edematous area within the vascular arcades, avoiding the foveal center (500 μm radius from the anatomical foveola, estimated on OCT) on the first treatment session. When the patient returns for the first post-laser follow-up in four to six weeks, and if no detectable pigmentary disturbances are seen on clinical examination, OCT or on the fundus autofluorescence image, then the previous laser parameters can be safely used in any subsequent MicroPulse laser sessions. Remember that treatment through the fovea is not always necessary: It is typically performed when persistent foveal edema is present at three months following the initial laser session. OM

OM’S GUEST EDITORS FOR JULY:
	Thomas Albini, MD, is associate professor of clinical ophthalmology, Bascom Palmer Eye Institute, Miami, FL. A uveitis expert, he has more than 110 peerreviewed journal articles in PubMed.
	Sam Mansour, MD, MSc, FRCS(C), FACS, is medical director of the Virginia Retina Center and is a clinical professor of ophthalmology, George Washington University. Dr. Mansour is a member of the Diabetic Retinopathy Clinical Research Network (DRCRNet).