The objective of the study is to evaluate the efficacy of a new pattern of argon-laser in treating patients with proliferative diabetic retinopathy (PDR).

Argon-laser pan retinal photocoagulation (PRP) is the first-line therapy for proliferative diabetic retinopathy (PDR) nowadays, which is believed to function by reducing retinal ischemia and decreasing the stimulation for neovascularization. However, diabetic retinopathy (DR) would still progress uncontrollably even after PRP, and PRP would result in reduction in visual acuity and loss of peripheral visual field, which may be influenced by the distribution pattern of the retinal laser treatment.

A variety of modified argon-laser patterns have been reported - a more central PRP, a more peripheral PRP, a central-sparing PRP or an extended-targeted PRP, yet the risk of developing neovascularization is higher in retina around the posterior vascular arcades and alongside the major retinal vessels.

This study will include 300 patients with PDR, who will be treated with a new pattern of argon-laser. An initial retinal laser would be given in the posterior retina outside the arcades and the mid-peripheral retina flanking the large vessels. Then investigators will conduct no less than 2 years follow-up. Further peripheral PRP and anti-VEGF administration would be added only if neovascularization progress, aiming to stop DR progression with the minimum of laser energy.

Inclusion Criteria:

1. Having given free and informed consent to take part in the study.
2. Diabetes mellitus (DM) under stable treatment during the study, aged 18y to 70y, with no significant underlying systemic diseases (such as impaired renal function, severe cardiac disease, etc.);
3. Clinically diagnosed PDR, with the presence of neovascularization confirmed by ultra-widefield fundus photography and widefield OCT angiography.

Exclusion Criteria:

1. Previous treatment with PRP;
2. Previous treatment with anti-VEGF agents or corticosteroids within 3 months;

2. Severe cataract, massive vitreous hemorrhage, or extensive preretinal hemorrhage that makes pan retinal photocoagulation impossible; 3. Unable to tolerate argon-laser retinal treatment.; 4. Vitreous macular traction or traction retinal detachment need to be performed with vitrectomy; 5. Retinal vascular occlusion, age-related macular degeneration, retinal angioma, uveitis, glaucoma, optic neuropathy, or other ocular diseases that can lead to vitreous hemorrhage and/or neovascularization; 6. Other conditions that the researcher found improper to be included into this study.