I sometimes get crossed eyes after meditating for extended periods of time. I usually shift my awareness between different sensations, like sounds, body awareness, closed-eye visuals, etc, as well as thoughts and third-eye visualizations. I try to keep myself as relaxed as possible, although sometimes it's not so easy to tell just how relaxed I am, especially when it comes to my eyes. Am I doing something wrong since I'm getting crossed eyes? (everything is a little blurry and I see bright objects in double...takes a while before my eyes return back to normalcy..)
As far as the practice goes, try to keep your awareness on just one thing. Other things arise, but let them go and drift your awareness back to the focus. Just choose one, focus and when the object of focus becomes clearer, focus until it's even clearer. Slowly with that practice, the senses withdraw from the outside world, and from the urge to observe things. Let them lie in stillness. I would guess that right now you're trying so hard to focus on things with your physical eyes that you're going bug eyed! haha. Just focus on one thing with a quiet attitude, letting everything else go.
Use hrit padma as central focus. This shouldn't be taught over the internet but here it is. Below the breastbone about an inch is the floating rib cage. It is a small bone. In front of that about an inch is where your 'all-around meditation focus' might be best. This is the theoretical center of the body. Now then if and when when you start to feel too emotional then you switch maybe to the head center for awhile. See if that framework fits. Peace. I want to add that hrit padma is not the heart proper but a 'heart of the body and mind.'
