The Freiburg Visual Acuity Test???Automatic Measurement of Visual Acuity

• Published in: Optometry and vision science Vol. 73; no. 1; pp. 49 - 53
• Main Author: BACH, MICHAEL
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott Williams & Wilkins 01.01.1996
• Subjects: Biological and medical sciences; Diagnosis, Computer-Assisted; Evaluation Studies as Topic; Humans; Investigative techniques of ocular function and vision; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Patient Acceptance of Health Care; Self Administration; Sensory Thresholds; Vision Tests - instrumentation; Visual Acuity; Human; Self evaluation; Automatic measurement; Visual acuity; Exploration; Measurement method; Computer aid
• ISSN: 1040-5488
• DOI: 10.1097/00006324-199601000-00008

The Freiburg Visual Acuity test is an automated procedure for self-administered measurement of visual acuity. Landolt-Cs are presented on a monitor in one of eight orientations. The subject presses one of eight buttons, which are spatially arranged on a response box according to the eight possible positions of the Landolt-Cs' gap. To estimate the acuity threshold, a best PEST (best Parameter Estimation by Sequential Testing) procedure is used in which a psychometric function having a constant slope on a logarithmic acuity scale is assumed. Measurement terminates after a fixed number of trials. With computer monitors, pixel-discreteness artifacts limit the presentation of small stimuli. By using anti-aliasing, i.e., smoothing of contours by multiple gray levels, the spatial resolution was improved by a factor of four. Thus, even the shape of small Landolt-Cs with oblique gaps is adequate and visual acuities from 5/80 (0.06) up to 5/1.4 (3.6) can be tested at a distance of 5 m.