Visual agnosia is the failure to recognize visual stimuli despite normal attention, intelligence, la

1

• Visual agnosia is the failure to recognize visual
  stimuli despite normal attention, intelligence,
  language and visual perception. As in all
  agnosias, the patient is unable to derive meaning
  from the preserved primary sensory input.
• Associative visual agnosia consists of two
  subsyndromes object agnosia, or the inability to
  recognize objects, and prosopagnosia, the
  inability to recognize faces. Patients with
  visual object agnosia also have prosopagnosia,
  but those with prosopagnosia do not necessarily
  have visual object agnosia.

2

• Patients with visual agnosia recognize real
  objects better than line drawings of objects.
  They also recognize common objects like a fork or
  pen more easily than such objects as a
  stethoscope or city skyline, which are uncommon
  or complex.

3

• Prosopagnosia, a distinct form of visual agnosia,
  is characterized by the inability to recognize
  previously known faces and an impairment in
  learning and recognizing new faces.
• These patients look in the mirror and dont
  recognize their own image. When patients with
  prosopagnosia look at a face, they can identify
  the nose, eyes, cheek and mouth, and can describe
  the whole as a face, but they cannot tell you
  whose face it is.

4

• Although prosopagnosia is defined by this
  impairment in recognizing human faces, the defect
  affects visually triggered memory more generally
  extending to other classes of visually related
  stimuli. Thus, there is not only a defect in
  visual identification of relatives and friends,
  but also in recognition of specific types of cars
  (e.g. Cadillac versus Volkswagen), birds (e.g.
  eagle versus owl), trees (e.g. pine versus oak)
  and so on.

5

• In contrast to visual object agnosia, recognition
  of classes of objects in prosopagnosia is
  preserved. Despite inability to recognize
  specific members within a class of objects,
  patients with prosopagnosia correctly identify
  the class itself, e.g. car versus tree.
• Prosopagnosia usually develops suddenly, and
  patients realize that a relatives or their own
  face appears unfamiliar. Patients can identify
  their spouses by voice, perfume, body shape or
  clothes, but they perceive spouses faces as
  foreign. The recognition of familiar individuals
  by voice and other clues indicates that
  intelligence and memory are intact.

6

• Balints syndrome is rare and presents as one of
  the most dramatic behavioral disorders. Patients
  appear blind at first glance they are unable
  visually to detect new stimuli approaching them,
  fail to see a car pass in front of them, bump
  into walls and furniture, and make wild,
  inaccurate movements when reaching for things.
  They can often describe minute visual details
  that require normal visual acuity.

7

• The central feature of the syndrome is
  simultanagnosia. Simultagnosia is the inability
  to perceive the visual field as whole, sometimes
  called piecemeal vision. Thus, patients with
  simultanagnosia are unable to see more than one
  or two objects at one time they usually see only
  with macular vision, which provides good acuity
  but only captures a tiny fraction of the visual
  field and experience unpredictable jumping of
  focus from sector to sector.
• Patients complain that just when they find the
  target stimulus, it disappears.

8

• Oculomotor apraxia or psychic paralysis of gaze,
  is the inability voluntarily to direct gaze
  toward a specific part of the visual field.
  Thus, even if the patient is told where to look
  to see an object, he has difficulty directing
  foveal vision to that spot. Normally, when a
  novel stimulus enters our peripheral vision, we
  make a saccadic eye movement to bring foveal
  vision in line with that stimulus. In oculomotor
  apraxia, however, absent or inaccurate saccades
  render the subject functionally blind.

9

• Optic, or visuomotor, ataxia is the inability to
  direct movement of an extremity using visual
  guidance. The patient sees the pen she wants to
  pick up, and the right hand moves to grasp it,
  but the pen eludes her.