Snellen Chart Eye Test
ByA Snellen chart is an eye chart used by eye care professionals and others to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart during 1862.
The person being tested stands 20 feet from the chart and reads as many of the symbols as possible, reading each line and proceeding downward from the top.
A score is assigned in the form of a ratio, comparing the subject’s performance to that of a statistically normal subject’s performance. For example, a person who can read at 20 feet what the average person can read at this distance has 20/20 vision, whereas a person who can read at 20 feet what the average person can read at 40 feet has 20/40 vision.
Only the ten Sloan letters C, D, E, F, L, N, O, P, T, Z are used in the traditional Snellen chart. The perception of five out of six letters (or similar ratio) is judged to be the Snellen fraction.
The evolution of letter charts from Snellen’s original chart to the ETDRS chart, which is considered today’s gold standard, push practitioners and researchers from all parts of the world turn to ETDRS charts and other high-quality vision testing tools. Now are available the LCD Chart systems: unique solutions for both monocular and binocular tests.