Focal and diffuse DME: Which patients are candidates for MicroPulse?

I consider there to be two approaches for MicroPulse laser (Iridex) when you're dealing with diabetic macular edema (DME). One is when you have focal macular edema that does not involve the fovea. Here it is possible to do MicroPulse monotherapy, eliminating the need for injections.

The other situation is when you have either diffuse macular edema or focal edema that involves the fovea. In this situation, you're going to also require some form of injection therapy, whether it's anti-VEGF or steroids, or a combination of the two.

Focal DME involves localized leakage from microaneurysms and often presents less macular thickening, better visual acuity, and less severe retinopathy severity than diffuse DME. Focal DME may or may not involve the fovea.

Diffuse DME always involves the fovea, and the leakage usually involves the entire circumference of the fovea. Therefore, there is no definable demarcation around areas of leakage. When it comes to the ideal candidate for MicroPulse therapy, I would say there are patients in both categories. I use MicroPulse on patients with focal DME, for example, who are developing edema that could threaten the macula. With successful MicroPulse therapy, the patient would be able to avoid injections.

I will also use MicroPulse on patients with diffuse DME who receive repeated injections. Here I want to reduce the disease severity and lower the burden of injections.

It takes a while for the effect of MicroPulse treatment to take hold. There have been times when I have seen a result in a month, but I am more likely to see improvement over the course of three to six months. Foveal involvement generally affects visual acuity, so I want reduction of edema involving the fovea as soon as possible. I begin injections, which take effect more quickly, and then also do MicroPulse laser therapy after the edema has improved, which reduces the number of injections.

Reducing the burden of injections is important for patients who aren’t inclined to be compliant, and it can also be very important for patients with the best of intentions. A broken hip or cancer treatment can keep a patient away and lead to a reversal of progress. Fewer injections also mean a reduction in the risk of endophthalmitis.

Unlike continuous-wave laser therapy, MicroPulse lasers are active in short bursts. The resting intervals between the bursts allow tissue to cool between pulses and reduce thermal buildup within the tissue directly targeted by the laser. Instead of thermal necrosis, you get a stress response that induces a biological effect.¹

In my experience, the process is non-ablative, and it doesn’t cause obvious pigmentary scarring. It can be repeated, and it doesn’t preclude further treatments.

It’s always important to consider treatment options wisely, but the reality is that whether or not to treat a given patient with MicroPulse is not a dire decision. A negative result is just a lack of response.

Reference

1. Inagaki K, Shuo T, Katakura K, Ebihara N, Murakami A, Ohkoshi K. Sublethal photothermal stimulation with a micropulse laser induces heat shock protein expression in ARPE-19 cells. Journal of ophthalmology. 2015;2015729792.

Related Content: Imaging | Ophthalmology | Diabetic Macular Edema