I previously was very reluctant about using subthreshold laser for the treatment of retinal disorders. I considered it somewhat of a “homeopathic laser” because of the lack of a visible endpoint. Conversely, I had never enjoyed performing conventional laser therapy for macular edema because I felt it to be a very destructive procedure. However necessary conventional laser has been, I still view it as a form of “retinal amputation,” causing irretrievable tissue loss. When I first performed subthreshold laser therapy for macular edema in the early 1990s, I was pleasantly surprised with the limited tissue response in the absence of visible photocoagulative damage. MicroPulse Laser Therapy (MPLT) takes subthreshold to even safer levels, allowing a phototherapeutic treatment without any photodestruction. I believe that the 577 nm laser used with MPLT settings is the safest laser to use in the sensitive area of the fovea—not only around the fovea, but when treating refractory edema over the fovea.
One of my first cases was treating a patient with diabetic macular edema (DME) and cataracts, with no prior pharmacotherapy. The patient's vision was 20/30-1, largely due to diffuse foveal thickening and hard exudate formation. I did a single grid application of 577 nm MPLT and was amazed at the fact that the vision improved to 20/20-2 in less than 2 months with no visible signs of laser treatment, neither clinically nor on fluorescein angiography or spectral-domain optical coherence tomography (SD-OCT).
As I became more comfortable performing MPLT, I found that it gives me a large safety margin. I no longer have to “tiptoe” through the region of the fovea because I am not concerned about photocoagulative damage. I am able to treat quickly in an almost preset format, and my laser sessions take half the time than with a conventional focal and grid laser session. MPLT has significantly boosted my efficiency in the clinic.
My combination treatment algorithms
I have found that using 577 nm MPLT in combination with pharmacotherapy is an option that works well for my patients with DME. I use MPLT to confluently cover all areas of retinal edema.
For mild DME with a central subfield mean thickness (CSMT) of ≤250 μm as determined by SD-OCT, I primarily use MPLT (See Parameters for Treating DME Using the IQ 577 Laser System).
For moderate macular edema, CSMT 251-400 μm, I typically start with 2 monthly intravitreal anti-VEGF injections and, if 30 days after the second injection there is no significant reduction in the edema, I proceed to MPLT. If there is a response to the initial 2 injections, I will continue to a maximum of 3 additional injections before proceeding to laser treatment.
For severe macular edema, CSMT >400 μm, I start with 3 monthly injections of an anti-VEGF agent and if the patient responds, I will continue to a maximum of 3 additional injections. If, following the anti-VEGF injections the CSMT on OCT is reduced to less than 400 μm, I proceed to MPLT. If there is an insufficient response following the anti-VEGF (CSMT >400 μm), I will then consider the option of intravitreal corticosteroids with the patient weighing the risks and benefits of that therapy, and if I choose to inject intravitreal triamcinolone acetonide, 30 days later I will apply MPLT again.
Positive impact to my practice and patients
In my practice, tissue-sparing MicroPulse has now completely replaced conventional continuous-wave (CW) laser for macular edema resulting from diabetes or retinal vein occlusion. I have used more laser therapy in comparison to pharmacotherapy alone on patients with macular edema in the last year than I have for the past 3 years due to the success that I have had with MPLT.
One consideration on which the patient should be advised is that with MPLT, there will probably not just be a single session. Typically, 2-3 sessions, 3-4 months apart will be required. MPLT is repeatable because it does not induce thermal damage. And, because this is the safest way to reduce edema, it is plausible it will take longer than conventional laser to achieve the desired result. As a result, MPLT has definitely increased our practice revenue because I am performing more laser treatments.
Additionally, I am performing more laser therapy because the indications for MPLT are wide. DME represents the bulk of my cases (Figure 1), but I also use MPLT to treat macular edema secondary to retinal vein occlusion, chronic uveitis, and in rarer cases, even pseudophakic macular edema. MPLT has proved to be very versatile.
When treating refractory edema, I have found that MPLT has helped me significantly. We all have those patients for whom pharmacotherapy with anti-VEGF agents and steroids fail to completely resolve the macular edema. These patients plateau to a point where the edema just fails to resolve or keeps recurring. It is very likely that if a patient does not respond after 3 consecutive injections with an anti-VEGF agent or steroid, they will not respond any better to subsequent injections. For these patients, I can use MPLT to shrink the residual edema without injecting again.
Given a choice between MPLT and pharmacotherapy for my patients who have mild to moderate DME, I have found that my younger working patients opt for MPLT. Their work and family obligations keep their schedule very busy and they typically don't have time for monthly visits. Patients who are confined to wheelchairs also find this a more convenient option.
One of the interesting findings with MPLT is that most of my patients have experienced a subjective improvement in their vision, typically within 2-3 weeks after treatment.
The ideal goal with any therapy for DME is to achieve the greatest reduction in macular thickness in the shortest time, with the least amount of side effects, and with the longest duration. Although pharmacotherapy is playing a larger role, laser therapy is still a key factor in treatment. In my practice, subthreshold MPLT has proven to be as effective as conventional laser, but with a greatly reduced risk of iatrogenic, nontherapeutic effects, and has improved my options to better manage patients with DME and other retinal disorders.
Sam E. Mansour, MSc, MD, FRCS(C), FACS, is Clinical Professor in the Department of Ophthalmology at George Washington University in Washington, DC, and is Medical Director of the Virginia Retina Center with 3 locations in Northern Virginia. Dr. Mansour states that he is a consultant to Iridex and QLT. He may be reached via email at SM@virginiaretina.com.