Many visual skills are important when reading.
Saccades are the very quick eye movements your eye make when you are reading. They happen over an incredibly short time at very high speeds. Your eyes dart from word to word, quickly stopping (fixating) and then continuing onward.
In order to read, it is necessary for the eyes to maintain proper convergence. When they don't, a person with convergence insufficiency may be able to read without initial problems, but quickly become tired, get double vision, get blurry vision, or have headaches.
If you or your child is having difficulty reading, there are many ways to improve reading skills. First, get a full vision exam. That may reveal problems caused by underlying vision issues. Once you confirm it is or is not a vision issue, you should make sure you have good lighting, have proper glasses, and practice reading regularly.