[Early treatment diabetic retinopathy study (ETDRS) visual acuity].

Human visual acuity is used as an indicator in everyday clinical work and ophthalmological studies to decide on therapy indications and success. This extensively used parameter needs a very structured workflow in order to preserve validity and prevent bias. Therefore, it should be kept in mind that especially in clinical studies investigators should strictly adhere to the study protocol. The intention of this article is to impart interesting facts about the early treatment diabetic retinopathy study (ETDRS) on visual acuity assessment, adhering to the original protocol of the ETDRS dating back to 1979-1989. Furthermore, the history of visual acuity assessment protocols prior to ETDRS, namely those of Snellen and Bailey-Lovie and finally the logMAR system will be discussed.