This could also be that you are straining too hard to close your eyes. Often, people new to meditation, will try and force their eyes to be shut hard, and sometime also roll their eyes upward when meditating, as if it somehow helps to reach the meditative state. This mainly causes eye strain and pains, and could be having an effect on the nerves around the eyes which I guess could be the cause of the shaking...
So, perhaps just try and relax a little more, let the eyes just restfully close and meditate without trying too hard.
Hugs
Giles