The visual acuity (VA) of patients with very low vision is classified using the semiquantitative scale "counting fingers" (CF), "hand motion" (HM), "light perception" (LP), and "no light perception." More quantitative measures would be desirable, especially for clinical studies. The results of clinical VA measurements, Early Treatment Diabetic Retinopathy Study (ETDRS) charts, and the Freiburg Visual Acuity Test (FrACT) were compared. The FrACT is a computerized visual acuity test that can present very large Landolt C optotypes when necessary. Examined were 100 eyes of 100 patients with various eye diseases (e.g., diabetic retinopathy, ARMD), covering a range of VAs from LP to decimal 0.32. The FrACT optotypes were presented on a 17-inch LCD monitor with random orientation. After extensive training, two ETDRS and FrACT measurements were obtained. The testing distance was 50 or 100 cm. ETDRS and FrACT coincided closely for VA > or = 0.02 (n = 80). ETDRS measures were successfully obtainable down to CF (at 30 cm; test-retest averaged over all patients, coefficient of variation [CV](ETDRS) = 9% +/- 8%), and FrACT provided reproducible measurements down to HM (test-retest CV(FrACT) =12% +/- 11%). For CF (n = 6), both ETDRS and FrACT resulted in a mean VA of 0.014 +/- 0.003 (range, 0.01-0.02). The VA results of FrACT for HM (n = 12) were 0.005 +/- 0.002 (range, 0.003-0.009); the individual values were highly reproducible. No results were obtainable for LP (n = 2). The three acuity procedures concur above a VA of 0.02. The results suggest that the category CF at 30 cm can be replaced by 0.014, using ETDRS or FrACT. Using FrACT, one can even reproducibly quantify VA in the HM-range, yielding a mean VA of 0.005.