Subthreshold yellow micropulse laser for treatment of diabetic macular edema: Comparison between fixed and variable treatment regimen

Purpose: To compare the efficacy between fixed and variable treatment regimens of subthreshold yellow micropulse laser for the treatment of diabetic macular edema. Methods: This is a retrospective, comparative, 12-month study of 39 eyes: 24 eyes received fixed treatment regimen of subthreshold micropulse laser treatment and 15 eyes underwent variable treatment regimen of subthreshold micropulse laser, all eyes were followed up for 12 months. Subthreshold micropulse laser was performed with the following parameters: 100 μm spot size on slit lamp, 5% duty cycle of 0.2 s, and 250 mW power. To choose the power of the variable treatment regimen of subthreshold micropulse laser group, continuous laser power was titrated to a barely visible burn and then switched to MicroPulse mode, multiplying the test burn power by 4 and using a 5% duty cycle of 0.2 s. Main outcomes included changes in central macular thickness and best-corrected visual acuity. Results: At baseline, the mean LogMAR best-corrected visual acuity was 0.297 ± 0.431 in the variable treatment regimen of subthreshold micropulse laser group and 0.228 ± 0.341 in the fixed treatment regimen of subthreshold micropulse laser group. At the end of follow-up, the mean LogMAR best-corrected visual acuity was 0.289 ± 0.473 (p = 0.785) and 0.245 ± 0.376 (p = 0.480) in the variable and fixed treatment regimens of subthreshold micropulse laser groups, respectively. Similarly, central macular thickness decreased in both groups after treatment; at baseline, the mean central macular thickness was 371.06 ± 37.8 in the variable treatment regimen of subthreshold micropulse laser group and improved to 325.60 ± 110.0 μm (p = 0.025) at the end of the follow-ups, while it was 342.30 ± 35.4 in the fixed treatment regimen of subthreshold micropulse laser group and improved to 308.51 ± 67.5 (p = 0.037). Conclusion: Both treatment regimens are effective for the treatment of mild center-involving diabetic macular edema: fixed treatment appears more suitable minimizing treatment time and reducing the possible errors due to wrong titration in the switch from continuous to micropulse mode.