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An example of the Landolt C eye chart (also known as the Japanese eye chart). Numerous types of eye charts exist and are used in various situations. For example, the Snellen chart is designed for use at 6 meters or 20 feet, and is thus appropriate for testing distance vision, while the ETDRS chart is designed for use at 4 meters. [16]
A person taking the test covers one eye from 6 metres or 20 feet away, and reads aloud the letters of each row, beginning at the top. The smallest row that can be read accurately indicates the visual acuity in that specific eye. The symbols on an acuity chart are formally known as "optotypes". Variation of Snellen chart with another letter ...
Web apps are used by a variety of online sellers of eyeglasses where an object of known size, such as a credit card, is needed to assist (size reference) the measurement process. [ 13 ] [ 14 ] Some mobile apps have eliminated the need for a reference object to make accurate PD measurements by leveraging depth imaging and advanced algorithms now ...
Visual acuity with Distant chart with correctors Visual acuity with eye chart at Distant 20 feet (6 m) and with (cc: Latin cum correctore) correctors (spectacles); Dsc is without (sc: Latin sine correctore) correctors. See Visual_acuity#Legal_definitions: VA Nsc - VA Ncc Visual acuity with Near chart without correctors
For 6/6 = 1.0 acuity, the size of a letter on the Snellen chart or Landolt C chart is a visual angle of 5 arc minutes (1 arc min = 1/60 of a degree), which is a 43 point font at 20 feet. [10] By the design of a typical optotype (like a Snellen E or a Landolt C), the critical gap that needs to be resolved is 1/5 this value, i.e., 1 arc min.
An eyeglass prescription. Similar to medical prescriptions, eyeglass prescriptions are written on paper pads or included in a patient's electronic health record, and contain a number of different abbreviations and terms: DV is an abbreviation for distance vision. This specifies the part of the prescription designed primarily to improve far vision.
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