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Amblyopia. Anisometropia is a condition in which a person's eyes have substantially differing refractive power. [1] Generally, a difference in power of one diopter (1D) is the threshold for diagnosis of the condition . [2] [3] Patients may have up to 3D of anisometropia before the condition becomes clinically significant due to headache, eye ...
Esotropia is a form of strabismus in which one or both eyes turn inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. [1] It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called ...
Prism dioptres. Prism correction is commonly specified in prism dioptres, a unit of angular measurement that is loosely related to the dioptre. Prism dioptres are represented by the Greek symbol delta (Δ) in superscript. A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. [2]
Adult and child observers perceived a right heterotropia as more disturbing than a left heterotropia, and child observers perceived an esotropia as "worse" than an exotropia. Successful surgical correction of strabismus, for adult as well as children, has been shown to have a significantly positive effect on psychological well-being.
Esophoria is an eye condition involving inward deviation of the eye, usually due to extra-ocular muscle imbalance. It is a type of heterophoria. Cause. Causes include: Refractive errors; Divergence insufficiency; Convergence excess; this can be due to nerve, muscle, congenital or mechanical anomalies.
Rates among adults are between 15 and 49% while rates among children are between 1.2 and 42%. Far-sightedness more commonly affects young children and the elderly. Presbyopia affects most people over the age of 35.
Prism adaptation. Prism adaptation is a sensory-motor adaptation that occurs after the visual field has been artificially shifted laterally or vertically. It was first introduced by Hermann von Helmholtz in late 19th-century Germany as supportive evidence for his perceptual learning theory (Helmholtz, 1909/1962). [1]
Prism (optics) An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are not prisms. The most familiar type of optical prism is the triangular prism, which has a triangular base and rectangular sides.
Entropion is a medical condition in which the eyelid (usually the lower lid) folds inward. [1] It is very uncomfortable, as the eyelashes continuously rub against the cornea causing irritation. Entropion is usually caused by genetic factors. This is different from when an extra fold of skin on the lower eyelid causes lashes to turn in towards ...
Light-time correction is a displacement in the apparent position of a celestial object from its true position (or geometric position) caused by the object's motion during the time it takes its light to reach an observer. Light-time correction occurs in principle during the observation of any moving object, because the speed of light is finite.