Visual dyslexia, also known as surface dyslexia or dyseidetic dyslexia, is a type of learning disability in which the individual has difficulty recognizing whole words when reading, versus sounding out words phonetically. Learning specialists trained in subtypes of dyslexia refer to this deficit as a lack of sight vocabulary. Such an individual might also have trouble in correctly sequencing words when reading. He or she is typically able to accomplish written self-expression but might demonstrate a poor grasp of spelling rules, particularly in regard to words that are short but irregularly spelled. This subcategory of dyslexia is distinguished from auditory, phonological, or dysphonetic dyslexia, which relates to the inability to cognitively link the auditory and visual components of a given word.
A wide range of symptoms is possible in an individual who struggles with visual dyslexia. The person with this learning disability might visually confuse letters of the alphabet that have a similar spacial orientation, such as the lowercase letters q and p. Certain words that can have different meanings when the letters are reversed, such as the words "tab" and "bat," could also be confused by the person with visual dyslexia. When writing, someone with this condition might use phonetic spellings, like l-a-f for the word "laugh."
In the process of reading, individuals with visual dyslexia are likely to guess at a word based on its visual shape rather than making a sense connection with the full context of a sentence. They might also inadvertently transpose words within a phrase or read a word backward, due to visuospatial challenges. A traditional phonics-based approach to reading instruction is unlikely to help a person with visual dyslexia, because his or her learning deficit is based on lack of whole-word comprehension.
Another common form of dyslexia is called direct dyslexia, in which an individual is able to read aloud correctly but does not comprehend the meaning of the text. Dyslexia is a learning disability but does not indicate a person's overall intelligence, as it does not correlate with intelligence quotient (IQ). It is possible that an individual with dyslexia might also have attention deficit hyperactivity disorder (ADHD), but the relationship between these two conditions is not well understood. In general, dyslexia is believed to affect as many as 1 in 10 individuals, although scientific data is not available to back up this statistic as of 2011.