The condition causes eyeballs to move uncontrollably, which can affect vision and balance, but Reid has insisted that his son is just like every other youngster.
"Although Harry's eyes aren't the same as other children's, he doesn't need to wear glasses and is doing all the things he should at his age," Reid told the Daily Mail.
"He's inquisitive and he loves to draw pictures and read books, both of which encourage his eyes to focus. He can hold a pen nicely and writes really well."
Reid recently became a patron of charity Nystagmus Network.