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  2. Visual acuity - Wikipedia

    en.wikipedia.org/wiki/Visual_acuity

    In young humans, the average visual acuity of a healthy, emmetropic eye (or ametropic eye with correction) is approximately 6/5 to 6/4, so it is inaccurate to refer to 6/6 visual acuity as "perfect" vision. On the contrary, Tscherning writes, "We have found also that the best eyes have a visual acuity which approaches 2, and we can be almost ...

  3. Snellen chart - Wikipedia

    en.wikipedia.org/wiki/Snellen_chart

    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 ...

  4. Near visual acuity - Wikipedia

    en.wikipedia.org/wiki/Near_visual_acuity

    Near visual acuity or near vision is a measure of how clearly a person can see nearby small objects or letters.Visual acuity in general usually refers clarity of distance vision, and is measured using eye charts like Snellen chart, LogMAR chart etc. Near vision is usually measured and recorded using a printed hand-held card containing different sized paragraphs, words, letters or symbols.

  5. Myopia - Wikipedia

    en.wikipedia.org/wiki/Myopia

    A number of alternative therapies have been claimed to improve myopia, including vision therapy, "behavioural optometry", various eye exercises and relaxation techniques, and the Bates method. [122] Scientific reviews have concluded that there was "no clear scientific evidence" that eye exercises are effective in treating myopia [ 123 ] and as ...

  6. Refractive error - Wikipedia

    en.wikipedia.org/wiki/Refractive_error

    A distant object is defined as an object located beyond 6 meters (20 feet) from the eye. [citation needed] When an object is located close to the eye, the rays of light from this object no longer approach the eye parallel to each other. Consequently, the eye must increase its refractive power to bring those rays of light together on the retina.

  7. Human eye - Wikipedia

    en.wikipedia.org/wiki/Human_eye

    The vestibulo-ocular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement in response to neural input from the vestibular system of the inner ear, thus maintaining the image in the centre of the visual field. For example, when the head ...

  8. Apparent magnitude - Wikipedia

    en.wikipedia.org/wiki/Apparent_magnitude

    The faintest stars visible with the naked eye on the darkest night have apparent magnitudes of about +6.5, though this varies depending on a person's eyesight and with altitude and atmospheric conditions. [2] The apparent magnitudes of known objects range from the Sun at −26.832 to objects in deep Hubble Space Telescope images of magnitude ...

  9. Visual angle - Wikipedia

    en.wikipedia.org/wiki/Visual_angle

    The observers in experiment carried out by Murray and colleagues viewed a flat picture with two discs that subtended the same visual angle and formed retinal images of the same size , but the perceived angular size ′ of one was about 17% larger than for the other, due to differences in the background patterns for the disks. It was shown that ...