LOW VISION Resolving the clinical acuity categories “hand motion” and “counting fingers” using the Freiburg Visual Acuity Test (FrACT) C. Lange & N. Feltgen & B. Junker & K. Schulze-Bonsel & M. Bach Received: 15 April 2008 / Revised: 23 July 2008 / Accepted: 26 July 2008 / Published online: 3 September 2008 # Springer-Verlag 2008 Abstract Purpose The Freiburg Visual Acuity Test (FrACT) has been suggested as a promising test for quantifying the visual acuity (VA) of patients with very low vision, a condition often classified using the semi-quantitative clinical scale “counting fingers” (CF), “hand motion” (HM), “light perception” (LP) and “no light perception”. The present study was designed to assess FrACT perfor- mance in a sizable number of CF, HM, and LP patients in order to generate a setting for future clinical studies in the low vision range. Methods We examined a total of 41 patients (LP, n =11; CF, n =15; HM, n =15) with various eye diseases (e.g., diabetic retinopathy, ARMD), covering the clinical VA scale from LP to CF. The FrACT optotypes were presented at a distance of 50 cm on a 17-inch LCD monitor with four random orientations. After training, two FrACT measure- ments (test and retest) were taken, each comprising 30 trials. Results FrACT measures reproducibly the VA of CF and HM patients. In CF patients, FrACT resulted in a mean logMAR=1.98±0.24 (corresponding to a decimal VA of 0.010), for HM in a mean logMAR=2.28±0.15 (corresponding to a decimal VA of 0.0052). In all LP patients the FrACT values were close to what would be obtained by random guessing. The mean test–retest 95% confidence interval was 0.21 logMAR for CF patients and 0.31 logMAR for HM respectively. Test-retest variability declined from 24 to 30 trials, showing that at least 30 trials are necessary. Conclusion FrACT can reproducibly quantify VA in the CF and HM range. We observed a floor effect for LP, and it was not quantifiable further. Quantitative VA measures are thus obtainable in the very low-vision range using FrACT. Keywords Visual acuity . Low-vision assessment . Psychophysics Introduction Visual acuity (VA) is one of the most important ophthal- mological parameters in clinical studies. VA in the low- vision range is clinically assessed with the categories “counting fingers” (CF), “hand motion” (HM), “light perception” (LP) and “no light perception”; a scale that is only semi-quantitative and does not permit differentiation within those categories. Quantitative VA tests used in clinical studies—such as the Early Treatment Diabetic Retinopathy Study (ETDRS [1, 11])—only cover VA ranges down to CF [7, 14]. The values below the testing range of the ETDRS charts have been approximated, e.g., by using the Snellen charts [12, 13]. Holladay [13] estimated a VA decimal of 0.01 for CF and 0.001 for HM, whereas Grover et al. [12] estimated a VA decimal of 0.0025 for CF, 0.002 for HM, 0.0016 for LP, and 0.0013 for blindness. These estimates do not allow further differentiation of VA within the CF, HM and LP groups. It may, however, be important to detect minor differences within these categories in order to monitor Graefes Arch Clin Exp Ophthalmol (2009) 247:137–142 DOI 10.1007/s00417-008-0926-0 C. Lange : N. Feltgen : B. Junker : K. Schulze-Bonsel : M. Bach Department of Ophthalmology, University of Freiburg, Killianstr. 5, 79106 Freiburg, Germany M. Bach (*) Universitäts-Augenklinik Freiburg, Killianstraße 5, 79106 Freiburg, Germany e-mail: michael.bach@uni-freiburg.de