The grading of diabetic retinopathy is based on the concept that a hierarchy of stages can be defined, where the higher the grade, the higher the risk of suffering visual loss. The grading scale reflects the natural course of the disease in its unrelenting and most devastating form. In reality, diabetic retinopathy can regress both spontaneously and after therapeutic intervention. To construct or validate a grading scale, rates of progression to visual loss or another endpoint that is meaningful to the patient must be measured. Grading scales constructed for scientific and regulatory purposes, such as the study of new interventions, are made with the purpose of achieving maximum sensitivity for change in retinopathy. Interventional trials may then result in selected grades being validated and found useful for guiding interventions such as photocoagulation for proliferative diabetic retinopathy or diabetic macular edema. The timely identification of patients who reach interventional thresholds is the purpose subserved by simpler grading scales used in clinical screening practice.
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