Contrary to popular belief, high levels of chlorine do not irritate the eyes. There are only two factors that cause this discomfort:
The presence of chloramines (combined chlorine)
Unbalanced pH
A shock treatment without chlorine eliminates chloramines. Since the pH of the eyes is 7.5, water with a different pH will automatically cause irritation. This is why it is important to maintain the pH of the water between 7 and 7.4.