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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]
Pure alexia. Pure alexia, also known as agnosic alexia or alexia without agraphia or pure word blindness, is one form of alexia which makes up "the peripheral dyslexia" group. [1] Individuals who have pure alexia have severe reading problems while other language-related skills such as naming, oral repetition, auditory comprehension or writing ...
Convergence insufficiencyis a sensory and neuromuscular anomaly of the binocular visionsystem, characterized by a reduced ability of the eyesto turn towards each other, or sustain convergence. Symptoms. [edit] The symptoms and signs associated with convergence insufficiency are related to prolonged, visually demanding, near-centered tasks. They ...
Prism (optics) A familiar dispersive prism. 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 ...
Purpose. whether a person has strabismus. In the fields of optometry and ophthalmology, the Hirschberg test, also Hirschberg corneal reflex test, is a screening test that can be used to assess whether a person has strabismus (ocular misalignment). A photographic version of the Hirschberg test is used to quantify strabismus.
An estimated 2% to 5% of the general population—or 5 to 15 million Americans—are affected by strabismus. It usually develops in infants and young children and should be checked by an eye doctor.
Deep dyslexia. Deep dyslexia is a form of dyslexia that disrupts reading processes. Deep dyslexia may occur as a result of a head injury, stroke, disease, or operation. [1] This injury results in the occurrence of semantic errors during reading and the impairment of nonword reading. [2] [3]
Definition. The National Institute of Neurological Disorders and Stroke defines reading disability or dyslexia as follows: "Dyslexia is a brain-based type of learning disability that specifically impairs a person's ability to read. These individuals typically read at levels significantly lower than expected despite having normal intelligence.