The range of motion of the upper eyelid between an open and closed eye position is referred to as levator function. 0 to 6mm is considered poor levator function. 6 to 10mm is considered moderate levator function. More than 10mm is considered excellent levator function. The distinction is important as tells the surgeon what procedure is required to elevate an upper eyelid that lies too low over the eyeball at rest. If the function is poor a sling to the forehead frontalis muscle is required so that the eyebrow raising muscle can be recruited to raise the upper eyelid. If the function is moderate the aponeurotic connection between the eyelid elevating levator muscle and the upper eyelid cartilage is shortened. If the function is excellent the aponeurotic connection is sutured folded over itself or the adjacent smaller Muller’s muscle is shortened/removed. Every patient undergoing eyelid surgery should have the resting position and range of motion of their upper eyelids measured.