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Hyperopia or hypermetropia, from the Greek word "hyper-metropia : ὑπερ-μετρωπία" (''hyper'' = over + ''metro'' = measure + ''op'' = sight, look + suffix ''ia'' = condition, state > thus a condition of over-measured sight) commonly known as being farsighted (American English) or longsighted (British English), is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or the lens cannot become round enough), causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves toward the eye, the eye must increase its optical power to keep the image in focus on the retina. If the power of the cornea and lens is insufficient, as in hyperopia, the image will appear blurred. People with hyperopia can experience blurred vision, asthenopia, accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus,〔American Optometric Association. ''(Optometric Clinic ef_error_pres.htm "Refractive Error and Presbyopia." ) Refractive Source.com Accessed September 20, 2006.〕 another condition that frequently causes blurry near vision.〔American Optometric Association. ''(Optometric Clinical Practice Guideline: Care of the patient with presbyopia. )'' 1998.〕 Presbyopes who report good far vision typically experience blurry near vision because of a reduced accommodative amplitude brought about by natural aging changes with the crystalline lens.〔 It is also sometimes referred to as farsightedness, since in otherwise normally-sighted persons it makes it more difficult to focus on near objects than on far objects.〔Kazuo Tsubota, Brian S. Boxer Wacher, Dimitri T. Azar, and Douglas D. Koch, editors, ''Hyperopia and Presbyopia'', New York: Marcel Decker, 2003〕 The causes of hyperopia are typically genetic and involve an eye that is too short or a cornea that is too flat, so that images focus at a point behind the retina. The opposite of hyperopia is myopia. ==Signs and tests== A farsighted person has trouble reading the Jaeger eye chart (the chart for near reading), but find it easy to read the Snellen eye chart (the chart for distance). A general eye examination, or standard ophthalmic exam may include the following points; *Eye pressure measurement (Tonometry) *Refraction test, to determine the correct prescription for glasses *Retinal examination *Slit-lamp exam of the structures at the front of the eyes *Test of color vision, to look for possible color blindness *Tests of the muscles that move the eyes *Visual acuity, both at a distance (Snellen), and close up (Jaeger) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hyperopia」の詳細全文を読む スポンサード リンク
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