The word "dyslexia" simply means "difficulty reading words."  It is possible to acquire dyslexia later in life, when the brain is injured (e.g., by a stroke), but it is far more common for dyslexia to be "developmental," or present throughout an individual's life.  Although many people mistakenly believe that dyslexia means "reading words backwards," true directional reading issues are rare.  By far the most common problem individuals with dyslexia face is difficulty perceiving the individual sounds, or phonemes, within spoken words.   This "phonological" form of dyslexia makes it very hard for a child learning to read to learn to "sound out" words by matching letters or letter groups to the sounds he/she hears.  A second, somewhat less common form of dyslexia, sometimes referred to as "dyseidetic" dyslexia, makes it hard for a person to access a spoken word in response to a visual input.  Persons with this form of dyslexia may have difficulty learning to read words "on sight," or without letter by letter decoding. It is also possible to have both of these types of dyslexia at the same time.

Most people who have dyslexia DO eventually learn to read, but they may read differently, possibly even using different areas of the brain than readers who do not have dyslexia.  Even when a person with dyslexia does compensate and learns to comprehend what is read quite well, he/she may still have trouble with spelling, and may still read less accurately and efficiently than might be expected based on ability and educational history.

Difficulties with reading comprehension may or may not result from dyslexia, but are nonetheless a significant issue.  Similarly, weak reading fluency can have multiple causes.  Evaluation of all of these issues is necessary to determine what interventions and supports may prove most helpful.