Eye-Movement and Shape Keys

I wanted to create eye-movements with shape keys. But when I use the shape key slider to make the movement hapen, the eye rotates but also gets bigger.
So this is not a good method to make the eyes move or what am I missing here?
Thanks for any help and informations.

Shape keys work in a linear fashion, so depending on how you changed the eye position it could lead to some weirdness. Generally speaking, rotation doesn’t work well with shape keys. In other words, it may be harder to set up, but it would be better to control eye rotation with bones.

If you’re using a rigged mesh, then try using bones to move eyes that are their own separate meshes. Shape keys aren’t that well suited for rotation, as Safetyman says.