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Snellen chart is used to estimate visual acuity (last three rows are 20/15, 20/13 and 20/10) A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862 as a measurement tool for the acuity formula developed by his professor ...
Lea test. logMAR chart. An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. [1] Eye charts are often used by health care professionals, such as optometrists, physicians and nurses, to screen persons for vision impairment.
A person's visual acuity is registered documenting the following: whether the test was for distant or near vision, the eye(s) evaluated and whether corrective lenses (i.e. glasses or contact lenses) were used: Distance from the chart D (distant) for the evaluation done at 20 feet (6 m). N (near) for the evaluation done at 15.7 inches (400 mm).
Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision, is approximately 25 cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image. Viewing conditions.
Distance PD is the separation between the visual axes of the eyes in their primary position, as the subject fixates on an infinitely distant object. Near PD is the separation between the visual axes of the eyes, at the plane of the spectacle lenses, as the subject fixates on a near object at the intended working distance.
A 1951 USAF resolution test chart is a microscopic optical resolution test device originally defined by the U.S. Air Force MIL-STD-150A standard of 1951. The design provides numerous small target shapes exhibiting a stepped assortment of precise spatial frequency specimens. It is widely used in optical engineering laboratory work to analyze and ...
Vertex distance is the distance between the back surface of a corrective lens, i.e. glasses (spectacles) or contact lenses, and the front of the cornea. Increasing or decreasing the vertex distance changes the optical properties of the system, by moving the focal point forward or backward, effectively changing the power of the lens relative to ...
Sloan letters. True Sloan letters as described in the original article of Louise L. Sloan (1959). Sloan letters, designed by Louise Sloan in 1959, are a set of optotypes used to test visual acuity generally used in Snellen charts and logMAR charts. This set of optotypes consists of ten specially formed "letters", C, D, H, K, N, O, R, S, V and Z ...
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