Visual acuity commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. the sharpness of the retinal image within the eye, the health and functioning of the retina, and the sensitivity of the interpretative faculty of the brain. A common cause of low visual acuity is refractive error, errors in how the light is refracted in the eyeball, and errors in how the retinal image is interpreted by the brain. The latter is the primary cause for low vision in people with albinism. Causes of refractive errors include aberrations in the shape of the eyeball or the cornea, and reduced flexibility of the lens. Too high or too low refraction is, respectively, the cause of near-sightedness or far-sightedness; normal refractive status is referred to as emmetropia. Other optical causes are astigmatism or more complex corneal irregularities.
| MeSH | D014792 |
| MedlinePlus | 003396 |
| LOINC | 28631-0 |
关于20/20
Created by ABC News, the news series features in-depth story package focusing primarily on human interest stories rather than international and political subjects.
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The series was created by Roone Arledge. The anchors on the premiere telecast were Esquire magazine editor Harold Hayes and Time art critic Robert Hughes.
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Angular diameter - The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is the angular aperture.. Dioptre - A dioptre or diopter is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres. It is thus a unit of reciprocal length. For example, a 3-dioptre lens brings parallel rays of light to focus at ¹⁄₃ metre.. Eye examination - An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, ophthalmologist, orthoptist, or an optician.. Fovea centralis - The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina.. Hyperacuity (scientific term) - The sharpness of our senses is defined by the finest detail we can discriminate. Visual acuity is measured by the smallest letters that can be distinguished on a chart and is governed by the anatomical spacing of the mosaic of sensory elements on the retina.. Landolt ring - The Landolt C, also known as a Landolt ring, Landolt broken ring, or Japanese vision test, is an optotype: a standardized symbol used for testing vision. It was developed by the Swiss-born ophthalmologist Edmund Landolt.. Optometry.. Visual perception.. Ophthalmology.. Medical signs.
