The investigators observed that the retinal oxygen saturation was a strong predictor of treatment response. Compared to patients whose disease was slowed down after treatment, patients with progression three months after PRP had an increase in the venous retinal oxygen saturation (+ 4.1% vs. -1.8%, p = 0.02). Patients with an increase of at least 3.0% in venous retinal oxygen saturation had 4.0 times greater risk of disease progression than patients who were below this threshold (15). This observation is in line with another Danish study, which demonstrated that worsening of DR causes increased venous retinal oxygen saturation (16). By measuring if this increase in venous retinal oxygen saturation has slowed down, one can assess whether PRP treatment is sufficient.