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Photophobia is a symptom of abnormal intolerance to visual perception of light.〔(thefreedictionary.com/photophobia ) citing: *Dorland's Medical Dictionary for Health Consumers. 2007 *The American Heritage Medical Dictionary Copyright 2007 *Miller-Keane Encyclopedia & Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. 2003 *Millodot: Dictionary of Optometry and Visual Science, 7th edition. 2009〕 As a medical symptom, photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical sensitivity of the eyes,〔(thefreedictionary.com/photophobia ) citing: *Gale Encyclopedia of Medicine. Copyright 2008 *Mosby's Medical Dictionary, 8th edition. 2009 *McGraw-Hill Concise Dictionary of Modern Medicine. 2002〕 though the term is sometimes additionally applied to abnormal or irrational fear of light such as heliophobia.〔(thefreedictionary.com/photophobia ) citing: *The American Heritage Medical Dictionary Copyright 2007 *Millodot: Dictionary of Optometry and Visual Science, 7th edition. 2009〕 The term ''photophobia'' comes from the Greek φῶς (''phōs''), meaning "light", and φόβος (''phobos''), meaning "fear".〔(φῶς ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕〔(φόβος ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕 ==Causes== Patients may develop photophobia as a result of several different medical conditions, related to the eye or the nervous system. Photophobia can be caused by an increased response to light starting at any step in the visual system, such as: *Too much light entering the eye. Too much light can enter the eye if it is damaged, such as with corneal abrasion and retinal damage, or if its pupil(s) is unable to normally constrict (seen with damage to the oculomotor nerve). * Due to albinism, the lack of pigment in the colored part of the eyes (irises) makes them somewhat translucent. This means that the irises can't completely block light from entering the eye. *Overstimulation of the photoreceptors in the retina *Excessive electric impulses to the optic nerve *Excessive response in the central nervous system Common causes of photophobia include migraine headaches, cataracts, Mild Traumatic Brain Injury (MTBI), or severe ophthalmologic diseases such as uveitis or corneal abrasion. A more extensive list follows: 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「Photophobia」の詳細全文を読む スポンサード リンク
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