Snellen chart

Snellen chart

A Snellen chart is a visual aid used to test a person's visual acuity. It contains letters of varying sizes and is typically placed at a standard distance of 20 ft in the United States or 6 m in the rest of the world. The chart is used to measure a participant's ability to read the letters accurately, with the smallest letters indicating the highest level of visual acuity.From: Medical Physics and Biomedical Engineering [2017], Characteristics of Technology Adoption by Older Adults with Visual Disabilities [2021], Handbook of Visual Optics [2017]

Optical and visual metrics

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Published in Pablo Artal, Handbook of Visual Optics, 2017

Antonio Guirao

In the most familiar acuity test, a Snellen chart is placed at a standard distance of 20 ft in the United States, or 6 m in the rest of the world. At this distance, the letters representing normal acuity subtend an angle of 5 minutes of arc, and the thickness of the strokes and of the interspaces subtends 1 minute of arc. This level is designated 20/20 (in the United States) or 6/6 (in the rest of world) and is the smallest line that a person with normal acuity can read at a distance of 20 ft.

Characteristics of Technology Adoption by Older Adults with Visual Disabilities

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Published in International Journal of Human–Computer Interaction, 2021

Hyung Nam Kim

A convenience sampling method helped to invite 20 older adults with visual disabilities residing in the State of North Carolina (See Table 1). Research participants should speak English, be 65 years old or older, and have visual disabilities (i.e., visual acuity level worse than 20/70, (World Health Organization, 2008)). A participant’s visual acuity was measured with a Snellen chart. The majority of participants were female (80%), European American (60%), and retired (65%).

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Optical and visual metrics

Characteristics of Technology Adoption by Older Adults with Visual Disabilities