Why are some people's eyes slightly crossed when it doesn't affect their vision?

Question

My friend mentioned that her eyes were slightly crossed, but it didn't affect her vision. Although I hadn't noticed before, after she'd said, I could suddenly see that they were, indeed, slightly crossed.

I didn't want to make a big deal out of it at the time in case she felt embarrassed, so I didn't ask her any questions about it or anything, but I'm wondering now what causes eyes to be slightly cross-eyed in this way?

Thanks.

Answer 1

The brain compensates beautifully, as long as the cross isn't too bad.

Answer 2

Crossed eyes are caused by either an imbalance of the muscles that control the eyes or the brain isn't sending equal directions to the muscles that control the eyes. If the difference is small there usually isn't any visual obstruction. There are exercises and special prescription glasses that can help balance out the muscles and make the eyes even.