What is the pathophysiology of visual agnosia in posterior cerebral artery (PCA) stroke?

Updated: Jul 30, 2018
  • Author: Erek K Helseth, MD; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

This refers to a lack of recognition or understanding of visual objects or constructs. It is a disorder of higher cortical function.

The strict diagnosis of visual agnosia requires intact visual acuity and language function. Most patients have bilateral lesions, sparing the visual cortex but disrupting or disconnecting visual information; this interferes with the information’s ability to reach parts of the visual association cortex, for reference to visual memories. The patient with visual agnosia can recognize objects presented to a nonvisual sensory system; for example, the patient can identify keys by palpating them or hearing them jingle.

True visual agnosia has been divided into apperceptive and associative subtypes. In apperceptive visual agnosia, patients cannot name objects presented to them, draw objects from memory, or identify or match objects, yet they can see and avoid obstacles when ambulating and detect subtle changes in light intensity.

In associative agnosia, patients can draw objects to command and can match them or point to them, but they cannot name them. Patients can see shapes and reproduce them in drawings, yet they do not recognize the identity of objects.


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