"a difficulty in reading due to a condition of the brain," 1885, from German dyslexie (1883), from Greek dys- "bad, abnormal, difficult" (see dys-) + lexis "word" (taken as "reading"), from legein "speak" (from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')") + abstract noun ending -ia. Dyslexic (n.) is recorded by 1946; dyslectic (adj.) by 1962.
Professor Berlin has written a very interesting monograph upon the disease called dyslexia, which he believes allied to the alexia, or word-blindness of Kussmaul. He gives a clinical history of six cases, collected during a period of twenty-three years, all having this peculiarity, that they could read aloud the average type, Jaeger three to five, only a few words in succession. These words were correctly spoken and without confusion or stammering, but as soon as a few words had been read the patients seemed anxious to get rid of the book, and, on being questioned, stated that they had an unpleasant feeling which they could not well define. ["The Satellite of the Annual of the Universal Medical Sciences," Philadelphia, November 1887]