Editing Visual acuity (section)

== Measurement ==
[[File:Manual hand eye test.jpg|thumb|Manual hand eye test in Ghana (2018)]]
Visual acuity is measured by a [[Psychophysics|psychophysical]] procedure and as such relates the physical characteristics of a stimulus to a subject's [[Perception|percept]] and their resulting responses. Measurement can be taken by using an [[eye chart]] invented by [[Ferdinand Monoyer]], by optical instruments, or by computerized tests<ref>{{Cite web |last=Strasburger |first=H |name-list-style=vanc |year=2014 |title=Software for visual psychophysics: an overview |url=http://www.visionscience.com/documents/strasburger/strasburger.html |publisher=VisionScience.com}}</ref> like the FrACT.<ref>{{Cite web |last=Bach |first=Michael |name-list-style=vanc |year=2016 |title=The Freiburg Visual Acuity Test |url=http://michaelbach.de/fract/}}</ref>

Care must be taken that viewing conditions correspond to the standard,<ref>{{Cite web |last=Visual Functions Committee |date=25 May 1984 |title=Visual acuity measurement standard |url=http://www.icoph.org/dynamic/attachments/resources/icovisualacuity1984.pdf |url-status=dead |archive-url=https://web.archive.org/web/20210507011137/http://www.icoph.org/dynamic/attachments/resources/icovisualacuity1984.pdf |archive-date=7 May 2021 |access-date=29 May 2015 |publisher=International Council of Ophthalmology}}</ref> such as correct illumination of the room and the eye chart, correct viewing distance, enough time for responding, error allowance, and so forth. In European countries, these conditions are standardized by the [[European Committee for Standardization|European norm]] (EN ISO 8596, previously [[DIN]] 58220).