Therapeutic Efficacy of Subthreshold Laser Photocoagulation using a Conventional Pattern Scan Laser for Macular Edema in a Retrospective Study

Abstract

Purpose: Subthreshold laser photocoagulation has emerged and is changing minimally invasive treatment for macular edema (ME) affected by retinal vascular diseases. However, this laser method requires specific photocoagulator, and it cannot be introduced at each facility. We investigated the efficacy of subthreshold laser photocoagulation using a conventional pattern scan laser (PS-STLT) in treating ME in clinical practice. Methods: We assessed the effects of PS-STLT treatment in 24 eyes of 24 patients with ME. Seventeen patients had diabetic retinopathy, five had branch retinal vein occlusion, and two had central retinal vein occlusion. All patients underwent PS-STLT treatment between December 2015 and May 2017. The average postoperative observation period was 5.5 ± 3.4 months. We evaluated the following parameters before the PS-STLT procedure and at one, two, and three months postoperative: best-corrected visual acuity using logMAR scores, center macular thickness (CMT), and total macular volume (TMV) as determined by optical coherence tomography (OCT). We fixed the 577-nm laser beam of a scanning laser photocoagulator at an area 100 μm in diameter, 20 ms, and selected a 2 × 2 grid scan pattern using an Area Centralis® lens. The initial laser power of the PS-STLT was 100 mW, and the laser was focused on a specific area of the ME identified by OCT. If spot lesions were visible on ophthalmoscopic examination, the laser power was decreased by 10 mW to avoid scarring. Results: The laser power was 76.7 ± 18.1 (50-100) mW and the total laser shots were 374.4 ± 243.9. The preoperative logMAR scores and TMV were 0.26 ± 0.32 and 9.7 ± 1.6 mm3, respectively. They were 0.28 ± 0.29 and 9.6 ± 3.1 mm3, at one month postoperative, 0.25 ± 0.32 and 9.6 ± 2.6 mm3, at two months, and 0.25 ± 0.31 and 9.3 ± 1.7 mm3 at three months. A significant reduction in TMV was observed at three months postoperative (P < 0.01), and the CMT had decreased by ≥ 20% in 10 of 24 eyes (41.7%) three months after PS-STLT treatment. Conclusion: These findings suggest that PS-STLT using a general pattern scan laser for the treatment of ME is effective.