In the right hands, MicroPulse laser therapy from Iridex is safe and effective for the treatment of several retinal diseases. I believe that when MicroPulse laser therapy fails, it has more to do with the treater than the treatment. Currently, Iridex has published general criteria, which is an excellent jumping-off point; however, if these parameters do not produce results after the first try, do not give up on it.
Settings are only part of the picture; laser distribution, density and the comfort level of the treating physician also play in. I reviewed my first 100 eyes treated with MicroPulse and found that my second 50 eyes did a lot better than the first 50. This is simply because I got more comfortable with how to perform and think about MicroPulse.
I use the Iridex IQ 532 nm (green) laser, which is sensitive to retinochoroidal pigmentation and necessitates titration to avoid over- or undertreatment. Before starting MicroPulse, I do a test spot outside the area of edema with the laser in continuous wave mode and standard settings. I begin at 50 mW power, 200 µm spot size and 200 millisecond duration, adjusting only the power up until a standard focal gray-white burn appears. I multiply that power setting number by three and then turn on MicroPulse mode at 5% duty cycle. For example, using my standard settings, if the burn appears at 90 mW, then the MicroPulse power setting is 270 mW at 5% duty cycle.
Regardless of pathology, I utilize the same settings: 200 µm spot size and 200 milliseconds duration. The only parameter I ever change is the power — I keep everything else exactly the same so that I have an accurate prediction of what the laser fluence will be once I go into MicroPulse mode (5% duty cycle). I vary pattern and distribution based on the pathology and treatment area.
My MicroPulse power settings range from a minimum of 150 mW to a maximum of 400 mW. Because MicroPulse technology may be more effective when treating near or even over the fovea, my maximum power setting is 400 mW to prevent any chance of damaging the fovea.
MicroPulse laser therapy changes the metabolism of the retina rather than cauterizing blood vessels and is most effective when administered in a dense distribution pattern where the spots nearly overlap. My practice is to extend the treatment area at least two laser spot widths beyond the edema. Using the upper left laser spot as a marker, I find a vessel, treat the whole area and then move on, always referring back to the upper left spot to avoid overtreatment of an area. The TxCell (Iridex) laser delivery pattern system simplifies this process. I set mine to 7 × 7 with zero spacing and then blanket the entire area of edema.
The type of disease dictates the pattern I use. Diabetic macular edema is the most common pathology I treat. I will typically treat visible microaneurysms with standard focal laser settings and then treat the rest of the edema in MicroPulse mode with spot counts generally in the hundreds (200 or greater).
For branch retinal vein occlusion, I do not employ any continuous-wave therapy. Using fluorescein to guide my treatment, I always treat over the fovea and the entire area of capillary nonperfusion, extending as far peripherally as possible using a wide-angle contact lens for visibility (Volk HR Wide Field). The large treatment area usually necessitates 500 or more spots.
Treating central serous chorioretinopathy can be tricky, so I usually reserve MicroPulse laser therapy only for my patients who have failed other treatments and present with diffuse vascular leak. I treat arcade to arcade, even in the areas where there is not fluid, with a dense pattern usually requiring at least 500 spots.
Don’t give up
My preference is to use the titration method. In addition to accommodating for eye pigmentation, titration ensures that everything is in working order — the fiber optic cable is not kinked, the mirror is properly turned to produce the expected treatment — and thus prevents undertreatment and potential failure. However, this may be less of a concern when using the 810 nm or 577 nm lasers, and Iridex guidelines have good historical data suggesting that 400 mW is safe for most patients.
Keep track of your data to get a sense of what works and what you prefer. You will need a little bit of time to become comfortable with MicroPulse laser therapy. If you are not getting results, tweak your settings and treatment distribution patterns. Simply put, MicroPulse laser therapy requires a complete paradigm shift from the approach we used with focal laser in the past.
Disclosure: Luo reports he is a consultant for AbbVie, Alimera, Allergan, Genentech, Iridex and Lumenis and receives research grands from Allergan and Lumenis.