Reduced Visual Acuity
How clearly detail is seen. With typical vision, sometimes called 20/20 vision, you can clearly see, at arms-reach, a single line as narrow as a tenth of a millimetre, that's about the width of a single human hair. So with typical vision, two human hairs next to each other, need a gap at least one tenth of a millimetre between them, to be seen clearly and separately. This measure is called visual acuity, or clarity of vision, and the 20/20 (or 6/6 as used in the UK) is the typical measurement, with bigger numbers meaning that only wider lines and gaps are visible. When things need to be bigger and separated further apart to be seen clearly, this is called Reduced Visual Acuity. Further reading: What Is CVI? Visual Acuity and Visual Acuity The Technical Stuff, Lessons: 3b Visual Acuity and 5b Reduced Visual Acuity. See also our section Visual Acuity - Free Resources, including link to sight-sim, a free programme (shown in image below) where any photo can be altered to show different levels of reduced visual acuity and / or reduced contrast sensitivity.
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