Image observation of laser spots from subthreshold micropulse laser (577nm) photocoagulation for macular edema

Abstract

Objective To observe the laser spots created by subthreshold micropulse laser (577 nm) photocoagulation for macular edema with a multi-wavelength photographic technique (F-10).Methods It was a prospective case-series study.Seventeen patients (19 eyes) with macular edema diagnosed by fundus fluorescein angiography (FFA) and optical coherence tomography (OCT) were included.Eight patients (10 eyes) were diagnosed with diabetic macular edema (DME),5 patients (5 eyes) with macular edema attributable to central retinal vein occlusion (CRVO) and 4 patients (4 eyes) with macular edema attributable to branch retinal vein occlusion (BRVO).First,the threshold energy (P) was tested by continuous wave laser photocoagulation,then with the detection of the F-10 in retro mode,19 eyes underwent subthreshold micropulse laser photocoagulation.The laser energy was based on P.Fundus color images and autofluorescence were obtained before and immediately after subthreshold micropulse laser photocoagulation.Changes in central macular thickness (CMT) and best corrected visual acuity (BCVA) before treatment and 1 month after treatment were compared with a paired t test and signed rank sum test,respectively.Results Immediately after treatment,in retro mode images,laser spots appeared under laser energy of 122.4％ P in 6 eyes,153.1％ P in 8 eyes and 183.7％ P in 5 eyes.There were no changes in fundus color images or autofluorecence in any of the eyes.After 1 month of treatment,CMT had significantly decreased compared to that before treatment (t=4.238,P＜0.01),BCVA showed no significant difference between pre- and post-treatment.Conclusion Retro mode imaging is useful to detect the invisible laser spots created by subthreshold micropulse laser photocoagulation,and can help to select the appropriate laser energy for treatment. Key words: Subthreshold micropulse laser; Macular edema; Laser spots; Laser energy; Retro mode