History

During the 1890s and early 1900s, a ophthalmologist named James Hinshelwood released a line of articles. In those articles he describes the cases of congenital blindness, which he says is a congenital defect occurring in children with normal and undamaged brains. In the book that he wrote in 1917, Congenital Word Blindness, he  stated that the primary disability was in the visual memory for words and letters, and described symptoms including inverted letter, and difficulties with spelling and reading comprehension.

In 1925 Samuel Orton met a boy that could not read and that had the symptoms of a person that had a stroke who couldn’t read anymore.He started studying reading difficulties and decided that there was a condition not relevant to brain damage, which made it difficult to read. Orton saw that reading deficits in dyslexia did not seem to stem from strictly visual deficits. He also believed that the condition was caused by the failure to establish hemispheric dominance in the brain.  

In adult subjects, the reading of a series of 66 tiny lower-case letters, 5 mm high, spaced 5 mm apart, first from left to right, and then from right to left, was more easily and quickly done in the left to right direction. For former dyslexic children, a substantial number read a series of 42 letters with equal speed in both directions, and some (10%) read better from right to left than from left to right. This is clearly linked to the dynamics of sight, as it disappears when the space between letters is increased, transforming the reading into spelling. 

In the 1970s, a new hypothesis emerged that dyslexia stems from a deficit in sound processing. As a result, affected individuals have difficulty associating sounds with the visual letters that make up written words.




We tried to find information on the distribution of dyslexia, but there was not any data on it since no one knows about it's origin.