If you are talking about the white mark in the center of the eye, it could be foreign matter sitting on the surface of the eye, like a hair, or goop that will be blinked away.
If it doesn't move when the rabbit blinks, it can be a scratch on the eye. Most of the time those are incredibly hard to photograph without fancy lights and equipment, so I am guessing it is something they rabbit got in its eye, like a hair, and coated it with eye goop, which happens naturally to protect the eye from sharp things.