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Mechanical Analysis of Eyelid Morphology

Liangliang Zhu and Xi Chen, Acta Biomaterialia (2013)       

From a mechanical instability perspective, a double-eyelid is a double-folded thin film structure on a curved substrate, caused by compression as the film “slides” on the substrate. The underlying mechanics issues, in particular the requirements for forming a double-folded structure, are studied using a modeling/simulation framework. A minimalist model is employed to explore the wrinkle-to-fold transition. Refined and enriched models are further developed based on anatomical structures, which demonstrate three critical factors for the formation of double-layer folding of the eyelid. First, a crease line in the eyelid is essential where the local bending rigidity is relatively weak. Second, the skin above the crease line should be thin and wide enough. Third, the skin below the crease line should be possessed with relatively large effective stiffness so it can be lifted as a whole when eyes open. When the eye is opened beyond about 40% of its initial wrinkle wavelength, the double-folded structure emerges. Various types of eyelid morphologies are discussed based on the mechanistic model. The study provides useful insights for surgery, cosmetics, morphogenesis, as well as microfabrication.

Simulation of the double-eyelid (right) and a real one (left).Simulation of the single eyelid

Simulation of the double (up) and single (down) eyelid.


Simulation of the  outer and inner double eyelid.

Simulation of the outer and inner double eyelid.  

The simulation, a whale’s eyelid, a horse’s eyelid and a human’s eyelid, from left to right.

Whale, horse and human eyelid.

                                                                                              the double-folding structure of the tortoise 's neck skin.

 Byond eyelid: turtle's neck skin


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 Thanks for the inspiring question. From a genetic perspective, the gene determining the eyelid form doesn't change with sex, and hence genetics cannot explain the difference of the probability of double-eyelid formation between male and the female. From the mechanical perspective, however, we demonstrated in our paper that the thinner skin and the bigger size of the eyelid are in favor of the formation of the double-eyelid. The thickness of the female is 17% thinner than that of the male (Y. Lee and K. Hwang, Surg Radiol Anat, 2002), meanwhile statistically the overall eyelid size of the female is on the same order of that of the male. This may explain why women are slightly more favored for having double eyelids, especially the popular female stars who have large eyes.


To understand that the sky is everywhere blue, it is not necessary to have travelled all round the world.

Linvia's picture

It's very interesting research. Single eyelid possibly only happens in Aisans. The mehanism of the folding of eyelids is also related to the skull structure. 

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