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  2. Pupillary distance - Wikipedia

    en.wikipedia.org/wiki/Pupillary_distance

    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. [ 2] 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. [ 3]

  3. Human eye - Wikipedia

    en.wikipedia.org/wiki/Human_eye

    The human eye is a sensory organ in the visual system that reacts to visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and keeping balance . Arizona Eye Model. "A" is accommodation in diopters. The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer ...

  4. Snellen chart - Wikipedia

    en.wikipedia.org/wiki/Snellen_chart

    In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres. At this distance, the symbols on the line representing "normal" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 6/6 (or 20/20), is the ...

  5. Amblyopia - Wikipedia

    en.wikipedia.org/wiki/Amblyopia

    Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. [ 1] It results in decreased vision in an eye that typically appears normal in other aspects. [ 1] Amblyopia is the most common cause of decreased vision in a single eye among children and ...

  6. Polymorphism (biology) - Wikipedia

    en.wikipedia.org/wiki/Polymorphism_(biology)

    v. t. e. In biology, polymorphism[ 1] is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. To be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population (one with random mating). [ 2]

  7. Eye chart - Wikipedia

    en.wikipedia.org/wiki/Eye_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 .

  8. Adaptation (eye) - Wikipedia

    en.wikipedia.org/wiki/Adaptation_(eye)

    Adaptation (eye) In visual physiology, adaptation is the ability of the retina of the eye to adjust to various levels of light. Natural night vision, or scotopic vision, is the ability to see under low-light conditions. In humans, rod cells are exclusively responsible for night vision as cone cells are only able to function at higher ...

  9. Compound eye - Wikipedia

    en.wikipedia.org/wiki/Compound_eye

    A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, [ 1] which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distinguish brightness and color. The image perceived by this arthropod eye is a combination of inputs ...