Tiny Muscle

One of the smallest muscles in your body is the superior tarsal (Müller’s) muscle, a tiny strip of smooth muscle in the upper eyelid that helps keep the eyelid lifted.

Unlike the main eyelid-lifting muscle, Müller’s muscle is controlled entirely by the sympathetic nervous system—the same “fight or flight” system that responds to stress and excitement. That’s why a disruption of this nerve pathway can produce a subtle drooping of the upper eyelid. This small muscle is also the reason certain eye drops can temporarily raise a droopy eyelid without surgery. Indeed, when we dilate patients in the office, we often use a drop that stimulates the sympathetic nervous system, so their eyes actually look more open after dilation!