#visual_impairment__visual_defect__vision_defect__visual_disorder  impairment of the sense of sight
  supertype:  disability__disablement__handicap__impairment  the condition of being unable to perform as a consequence of physical or mental unfitness; "reading disability"; "hearing impairment"
  subtype:  amaurosis__amaurosi  partial or total loss of sight without pathology of the eye; caused by disease of optic nerve or retina or brain
  subtype:  amblyopia  visual impairment without apparent organic pathology
  subtype:  ametropia  (ophthalmology) faulty refraction of light rays in the eye as in astigmatism or myopia
     subtype:  myopia__nearsightedness__nearsightednes__shortsightednes  (ophthalmology) eyesight abnormality resulting from the eye's faulty refractive ability; distant objects appear blurred
     subtype:  astigmia__astigmatism  (ophthalmology) impaired eyesight resulting usually from irregular conformation of the cornea
        subtype:  keratectasia  abnormal bulging of the cornea of the eye
        subtype:  keratoconus__keratoconu  abnormal cone-shaped protrusion of the cornea of the eye; can be treated by epikeratophakia
     subtype:  hyperopia__hypermetropia__hypermetropy__farsightedness__longsightedness__longsightednes  abnormal condition in which vision for distant objects is better than for near objects
        subtype:  presbyopia  farsightedness resulting from a reduced ability to focus caused by loss of elasticity of the crystalline lens with age
  subtype:  aniseikonia  visual defect in which the shape and size of an ocular image differ in the two eyes
  subtype:  anorthopia  distorted vision in which straight lines appear curved
  subtype:  aphakia  absence of the natural lens of the eye (usually resulting from the removal of cataracts)
  subtype:  blindness__blindnes__sightlessnes  lack of sight
     subtype:  anopia  sightlessness (especially because of a structural defect in or the absence of an eye)
     subtype:  snowblindness__snowblindnes  temporary blindness caused by exposure to sunlight reflected from snow or ice
     subtype:  eyelessness__eyelessnes  blindness due to loss of the eyes
     subtype:  figural_blindness__figuralblindnes  inability to see shapes and contours
  subtype:  color_blindness__colorblindnes__colour_blindness__color_vision_deficiency__colour_vision_deficiency  genetic inability to distinguish differences in hue
     subtype:  dichromacy__dichromatism__dichromatopsia__dichromia__dichromasy  a deficiency of color vision in which the person can match any given hue by mixing only two other wavelengths of light (as opposed to the three wavelengths needed by people with normal color vision)
        subtype:  red-green_dichromacy__redgreendichromacy__red-gree_color_blindness  confusion of red and green
           subtype:  deuteranopia__Daltonism__green-blindness  dichromacy characterized by a lowered sensitivity to green light resulting in an inability to distinguish green and purplish-red
           subtype:  protanopia__red-blindness__redblindnes  dichromacy characterized by lowered sensitivity to long wavelengths of light resulting in an inability to distinguish red and purplish blue
        subtype:  yellow-blue_dichromacy__yellow-blue_color_blindness  confusion of yellow and blue
           subtype:  tetartanopia__yellow-blindness  a form of dichromacy characterized by lowered sensitivity to yellow light; so rare that its existence has been questioned
           subtype:  tritanopia__blue-blindness  rare form of dichromacy characterized by a lowered sensitivity to blue light resulting in an inability to distinguish blue and yellow
     subtype:  monochromacy__monochromatism__monochromatic_vision__monochromaticvision__monochromia__monochromasy  complete color blindness; colors can be differentiated only on the basis of brightness
  subtype:  diplopia__double_vision  visual impairment in which an object is seen as two objects; "diplopia often disappears when one eye is covered"
  subtype:  hemeralopia__dayblindnes  inability to see clearly in bright light
  subtype:  hemianopia__hemianopsia  blindness in one half of the visual field of one or both eyes
  subtype:  quadrantanopia  blindness in one fourth of the visual field
  subtype:  metamorphopsia  a defect of vision in which objects appear to be distorted; usually due to a defect in the retina
  subtype:  nyctalopia__night_blindness__nightblindnes__moon_blindness  inability to see clearly in dim light; due to a deficiency of vitamin A or to a retinal disorder
  subtype:  photoretinitis  damage to the retina resulting from exposure of the eye to the sun without adequate protection
  subtype:  retinal_detachment__retinaldetachment__detachment_of_the_retina__detached_retina  visual impairment resulting from the retina becoming separated from the choroid in the back of the eye; treated by photocoagulation
  subtype:  tunnel_vision  visual impairment involving a loss of peripheral vision
  subtype:  xanthopsia  visual defect in which objects appear to have a yellowish hue; sometimes occurs in cases of jaundice

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