A 48-year-old woman with poorly controlled type 2 diabetes (HbA1c 10.2%) undergoes routine dilated fundoscopy. She is found to have multiple microaneurysms, dot-blot hemorrhages, and hard exudates in the four quadrants, but no cotton-wool spots, intraretinal microvascular abnormalities, or neovascularization. She is asymptomatic with visual acuity 6/6 in both eyes. Which investigation is most appropriate to determine if she requires immediate laser photocoagulation?