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K. Schulze–Bonsel, N. Feltgen, H. Burau, L.L. Hansen, M. Bach; Quantifying Visual Acuity in Lowest–Vision Patients using the Freiburg Visual Acuity Test . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1933.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The visual acuity (VA) of patients with very low vision is classified using the semi–quantitative ordinal scale "Counting Fingers" (CF), "Hand Motion" (HM), "Light Perception" (LP) and "No Light Perception". More quantitative measures would be desirable, especially as motion is a different visual sub–modality. We compared the results of clinical VA measures, ETDRS charts and the Freiburg Visual Acuity Test (FrACT). The FrACT is a computerized visual acuity test, which can present very large Landolt C optotypes when necessary. Methods: We examined 107 eyes of 100 patients with various eye diseases (e.g. diabetic retinopathy, or ARMD), covering a range of VA from LP to decimal 0.32. The ETDRS charts were presented at a distance of 50 cm or 100 cm. The FrACT optotypes were presented on a 17" monitor at a distance of 50 cm and viewed monocularly. The responses were entered by the examiner, based on the patients' verbal responses. After extensive training, two ETDRS and FrACT measures were obtained in a block design, alternating in successive patients (ABBA/BAAB). All statistical evaluations were done on the nearly normally distributed log(VA)=–MAR scale. Results: For VA ≥0.02, clinical VA, ETDRS and FrACT coincided closely without systematic deviation and with a mean CV of 15±;11%. ETDRS could successfully be obtained down to CF (test–retest, averaged over all patients, CVETDRS=9±;8%), FrACT provided reproducible measures down to HM (test–retest CVFrACT=12±;11%). For CF (n=6) both ETDRS and FrACT resulted in a mean VA of 0.014±;0.001 (range 0.01 to 0.02). The VA results of FrACT for HM (n=12) were 0.005±;0.001 (range 0.003 to 0.009), the individual values were highly reproducible. For HM no results could be obtained using ETDRS. In the 2 patients with LP no successful measurement could be carried out with ETDRS nor FrACT. Conclusions: The excellent agreement of the three acuity procedures above VA=0.02 cross–validates all three of them, in particular the less widely used FrACT. The clinical category "CF" can be replaced by 0.014 using ETDRS or FrACT, with the latter technique even reproducibly quantifying VA in the hand motion range, around a VA of 0.005.
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