Alexia (also known as acquired dyslexia) is a condition resulting from brain damage that causes the sufferer to be unable to read (when they had the ability to do so previously). Sometimes called visual aphasia, alexia is an acquired dyslexia and not developmental - the person had the ability to read before the brain damage caused the condition. This can be caused by damage caused by brain lesions, brain trauma, or stroke.
An example of alexia is pure alexia which is also known as word blindness. It is characterized in that sufferers can write but not read. Looking at a page of words the person cannot read or comprehend the words, even words that they themselves have written!