“My eyes are tired”

I can’t tell you how frequently I have heard people who feel that their eyes are “tired.” But what does it mean for an eye to be tired? Certainly it doesn’t mean that your eyes have been exercising too much! Usually people mean that their eyes feel the same way that their eyes feel when they are physically tired, often after having been awake for a long time. We can all imagine the feeling of having been up too late and feeling tired. One of the consequences of having eyes open all day and into a late night is that tears can evaporate off of the eye surface for all that time. Our eyes get relatively wet from being closed while sleeping. So, when people are up too late and feeling physically tired, their eyes have simultaneously “dried out.” The feeling of dry eye then is associated with feeling physically tired as well. If the eyes feel that way but the rest of the body doesn’t feel the same, people localize the feeling to their eyes. “My eyes are tired” really means “my eyes are feeling dry.”