Subthreshold micropulse laser is equivalent to standard laser for treating diabetic macular edema

1. In a randomized trial of about 250 patients with mild or moderate center-involving diabetic macula edema (DME), subthreshold micropulse laser (SML) was equivalent to standard laser based on best corrected visual acuity (BCVA) at 24 months.

2. Neither patient group had improved BCVA at 24 months, with decreases of 2.43 and 0.45 ETDRS letters in the SML and standard laser groups, respectively.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Diabetic macular edema (DME) is a common cause of vision loss in diabetic retinopathy. DME has long been treated with macular laser, although anti-VEGF injections are increasingly used, especially in severe cases or those involving the fovea, where laser is not feasible. Subthreshold micropulse laser (SML) uses smaller pulses and, unlike standard laser, does not destroy local retinal pigment epithelium or overlying photoreceptors. This multicenter trial randomized 266 patients with mild or moderate center-involving DME to receive SML or standard laser in order to compare their effects on central vision. In a per protocol analysis, patients receiving SML had a 2.43 letter decrease in best corrected visual acuity (BCVA) at 24 months compared to a 0.45 letter decrease with standard laser, indicating equivalence. There was no significant difference in end central retinal thickness, mean visual field deviation, side effects, need for rescue treatments, or patient-reported visual function. Patients in the SML group received significantly more laser treatments. This high-quality trial is not the first to show SML to be non-inferior to standard laser in the setting of DME, but is large and with a long follow-up period of two years. Of note, neither study group had improved BCVA or improvements in visual function scores at two years. SML presents potential benefits in that it is thought not to permanently damage the retina, although this makes assessing the extent of past laser treatment challenging as SML leaves no visible burn. This study provides valuable evidence in favor of SML as a first-line therapy for non-severe DME involving the macula.

Click to read the study in Ophthalmology

Relevant Reading: Treatment of diabetic macular edema

In-Depth [randomized controlled trial]: Subjects were recruited from 16 centers in the United Kingdom between 2017 and 2018. Eyes with mild to moderate non-proliferative diabetic retinopathy, central retinal thickness less than 400 um, and BCVA of 20/200 or better were included. The presence of center-involving DME and central retinal thickness were determined using optical coherence tomography (OCT). Mean central retinal thickness was 329 um. Participants and OCT graders were blinded to subjects’ group. A 577-nm laser with a standardized grid pattern was used for SML. A 532-nm neodymium-doped yttrium aluminum garnet (ND:YAG) laser was used for standard laser treatment, with threshold method to achieve a mild, visible burn. Participants were followed every three to four months for two years. The difference in change in BCVA for SML compared to standard laser was -1.98, with a 95% confidence interval of -3.93 to -0.035 (p=0.046). This difference fell within the pre-specified threshold for clinical significance of -5 letters. In a model adjusted for baseline BCVA, extent of baseline edema, and history of cataract surgery, SML remained non-inferior to standard laser. Rescue anti-VEGF treatments were given in 18% of SML patients and 21% of standard laser patients.  There were no serious adverse reactions related to study treatments, but 2% of participants had adverse reactions.

Image: PD

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