Saturday, September 8, 2012

Heavy eyelids when tired, and upward eyeball movement

A 2008 Scientific American article Why do our eyelids get so heavy when we are tired? tries to explain "heavy" eyelids when tired with fatigue of the levator muscles that open the eyelids, combined with general physical fatigue of the whole body. It drew very well educated critique, particularly from a second year medical school student. Whether fatigue is a major factor in "heaviness" of the eyelids is arguable. I'd like to make another point not mentioned by anybody. I'm sure you've seen or at least heard of a person showing white of the eye (sclera) when he's fast asleep and you force open his eye. In fact, with some training such as that in meditation, you can relax your body so much as to simulate the sleep state, and now if you feel it, your eyeballs tend to "float" up toward the upper eyelids. This is a spontaneous reaction in the sleep-like state, not done by intentionally moving your eyeballs up in full consciousness; the upward movement of the eyeballs is a natural reflection. Note that the direction is really toward the upper eyelids, not necessarily up toward the sky, because when your head is lying on the side, it's no longer up literally.

I believe this natural eyeball movement is related to the levator muscle relaxation, although I don't know the details nor can I prove this connection. In fact, it sounds counter-intuitive because the up-moving eyeballs are more likely to push open the eyelids. But maybe the balls are actually moving further into the orbit (cavity in which eyes are situated), in effect relaxing instead of contracting the levator.

By the way, if you have learned to reach the half-sleep state, not only are your eyeballs moved up (precisely, toward your upper eyelids), but you'll also feel heavier breathing, with absolutely no facial expression (contrary to advertisement pictures showing a fake "sound" sleep child or lady with a pleasing smile), exactly like a person in real sound sleep. A short nap like this after lunch, even when you sit in your chair, is particularly refreshing!