Dyslexia is a condition that affects one's capability to manipulate symbols and sounds. It ordinarily appears as difficulties in reading, going forwards and backwards from letters to words and sounds, to meaning. As people do whenever they read aloud, for example.
A dyslexic person's eyes see things just like a non-dyslexic's eyes. However with the dyslexic, the brain interprets the data received in different ways. You don't "catch" dyslexia, you're born with it. About 1 out of every 10 has some type of dyslexia, to some degree. Getting a test for dyslexia would be the best way to discover for sure whether or not an individual is dyslexic.
A dyslexic person can learn to do practically anything the non-dyslexics do, but dyslexics learn differently. They have to be taught in the way they can learn. Otherwise, they could never "comprehend it" on their own, then get discouraged and throw in the towel, thereby shutting out a complete sector of learning and possibilities for themselves.
Nowadays, school-age children are routinely screened for dyslexia, however it was not always that way. The truth is, it has only been during the last 15 or so years that screening and testing for dyslexia have been the rule, not the exception.
Most adults who graduated from elementary school more than 15 years ago have never been tested. Because of this there's around 2 million dyslexic adults in the USA by itself.
What makes them difficult to locate and help was the manner the educational system treated them as children. These were not appreciated. They got branded as dull, lazy, underachievers and mental defectives (which most were definitely not!) They were injured and embarrassed at their differences. As defense mechanisms to protect themselves, they worked out how to hide these differences.
Today you'll find them as people working at jobs far beneath what their intelligence would indicate they were capable of. This so as to avoid paperwork, needing to read anything in their work. An easy dyslexic test may well set them on the road to overcoming dyslexia and opening an entirely new world of possibilities...