Subthreshold micropulse diode laser and double frequency neodymium: YAG laser in treatment of diabetic macular edema: a prospective, randomized study using multifocal electroretinography

Abstract

Objective: The purpose of this study was to compare the efficacy of subthreshold micropulse diode (SDM) laser with double-frequency neodymium YAG (Nd:YAG) laser in treatment of clinically significant diabetic macular edema.

Methods: Forty-six eyes of 33 patients with clinically significant macular edema (CSME) caused by diabetic retinopathy were randomized to either SDM (810?nm) laser or the conventional double-frequency Nd:YAG (532?nm) laser. Primary outcome measures were: change in the central macular thickness as measured by optical coherence tomography (OCT) and change in macular retinal sensitivity measured using multifocal electroretinography (MfERG). Secondary outcomes were: change in best corrected visual acuity (BCVA) and contrast sensitivity.

Results: The group was divided in half, with 23 eyes assigned to SDM laser and 23 eyes assigned to double-frequency Nd:YAG laser. Mean follow-up period was 6 months. No statistically significant difference was noted in either the primary or the secondary outcome measures between the two groups. Macular thickness decreased from the baseline measures of 298.5?49.3 and 312.9?45.8??m to 274.9?62.9 and 286.7?32.8??m in the SDM laser and Nd:YAG laser groups, respectively. On MfERG, P1 implicit wave time delay at baseline changed from 46.27?4.9 to 45.27?3.4?ms in the SDM group and from 46.55?4.9 to 45.27?4.1?ms in the Nd:YAG group. MfERG recordings of 18 of the 23 eyes treated with double-frequency Nd:YAG laser showed areas of signal void as compared to 4 eyes treated with the SDM laser.

Conclusions: SDM laser photocoagulation showed an equally good effect on visual acuity, contrast sensitivity, and reduction of diabetic macular edema (DME) as compared to conventional Nd:YAG laser photocoagulation. MfERG recordings, however, suggest that SDM laser results in better preservation of electrophysiological indices.