Outcomes of 400 versus 600 micrometer spot size after single session multispots pattern scan panretinal photocoagulation

INTERVENTION: Arm 1: multispots pattern panretinal photocoagulation using 400 micrometer spot size Arm 2: multispots pattern panretinal photocoagulation using 600 micrometer spot size Laser photocoagulation is performed using pattern scan system (Valon pattern laser, Dual laser LTD OY, Vantaa, Finland), which is a Nd‐YAG 532 nm laser beam. The parameters are: 1) spot sizes of 200 or 300 micrometer with superquad 160 contact lens (laser spot magnification of 2.0; Volk Optical Inc., Mentor, OH) which equivalent to the retinal lesion size of 400 and 600 micrometer, respectively, 2) duration of 20 ms, 3) grid pattern of 4x4, 4) spot spacing of 1.5 widths apart, 5) intensity of gray‐white burn, titrated at the major vascular area, 6) distribution extended from vascular arcade to beyond equator, no closer than 2 disc diameter temporal to fovea, no closer than 1 disc diameter to the nasal optic disc. All treatments are performed under topical anesthesia. Duration of the procedures are approximately 4 to 6 minutes. The re‐treatment will be considered at 3 months and 6 months of follow‐up. The indications of retreatment are persistence or recurrence of the neovascularization. CONDITION: severe diabetic retinopathy (severe nonproliferative and proliferative diabetic retinopathy) PRIMARY OUTCOME: Macular thickness changes after multispots patter photocoagulation in both groups. ; Retinal thickness measurements are performed with SD‐OCT (Spectralis; Heidelberg Engineering, CA, USA). Scans are performed in fast high resolution pattern, 1024 x 526 resolution. All scans will be reviewed for the accuracy and manually adjusted by one investigator. SECONDARY OUTCOME: Visual acuity changes after multispots patter photocoagulation in both groups. ; Visual acuity will be recorded in ETDRS letters measured at 6‐meter charts. INCLUSION CRITERIA: severe diabetic retinopathy without macular edema (macular thickness of less than 350 micrometers by SD‐OCT)