Patients sometimes bring pictures of double eyelid double eyelid fold height that they would like their eyes to be. If the photo they bring is a person with average double eyelid fold height or low fold height, then I would agree with their desired double eyelid fold height. However, if they desire an excessively high double eyelid fold, then I would object by saying that their eyelid muscle cannot tolerate a high double eyelid fold. When a double eyelid fold is made, then the skin and the soft tissue is attached to the eye elevating levator muscle. If the levator muscle is already weak before the surgery, putting an extra load of weight by creating a double eyelid fold will make the eyelid muscle difficult to lift the eyes. Therefore, the person will look more tired after the double eyelid surgery rather feeling refreshed.
And for patients who have an excessively high double eyelid fold, surgically lowering the high double eyelid fold to a lower double eyelid fold will decrease the weight burden on the eye elevating levator muscle and thus the patient’s eyes will feel lighter.
Here is the mechanical model of high and low double eyelid fold heights according to the spring dynamics. Physics was used to analyze eyelid elevation in relations to the double eyelid fold heights.
The spring constants and is the stiffness of the springs which correspond to the upper and the lower upper eyelid skin respectively. Because the Asians’ upper eyelid skin becomes thicker in a cephalic direction, , the spring constant in the case of high double eyelid fold should be greater than , that in the case of low double eyelid fold as shown (a) and (b). The damping constant of the spring is shown as b. The force equilibrium equations of each system shown in (a) and (b) can be expressed as (X1) and (X2) respectively,
where and are the mass of the eyelid in the case of high double eyelid fold and low double eyelid fold respectively, and F is the force to lift the eyelid by levator muscle. When the velocity becomes zero so that the eye opens most widely, the first and second time derivatives of the displacements in (X1) and (X2) becomes zero. Equation (X3) and (X4) show the relations between the maximum displacement of the eyelid and the force. Therefore, the maximum displacements of the eyelid for the case of high double eyelid fold and low double eyelid fold can be derived as shown in (X5) and (X6).
The equation (X5) and (X6) show that the maximum displacement should be inversely proportional to the spring constant k. Therefore, the maximum displacement in case of the high double eyelid fold is less than that in the case of the low double eyelid fold as shown in (c) and (d). Consequentially, the spring modeling can explain why eyelid ptosis can occur just from the creation of a high double eyelid fold without any direct effect from the levator muscle and how eyelid elevation increases (resolution of eyelid ptosis) with lowered double eyelid fold.
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