Thin-Film Buckling Theory and Clinical Application of the Mechanism of Double Eyelid Formation.

BACKGROUND: The mechanism underlying the formation of upper eyelid creases has been the subject of extensive study and ongoing debate. This research aims to elucidate the principles of upper eyelid creases formation, leveraging the membrane bending theory from engineering mechanics. METHODS: We developed an anatomical model of the eyelid and implemented the finite element analysis. Preprocessing and mesh division were conducted using HyperMesh, followed by computational analysis with Abaqus. This approach enabled the observation of dynamic changes in the upper eyelid during eye opening and closing. RESULTS: The study reveals that natural upper eyelid crease formation is influenced by multiple factors. These include the softer texture of the upper eyelid skin and the suborbicularis oculi fat, reduced rigidity at the eyelid crease, optimal contraction force of the upper eyelid, and the strategic placement of the pre-tarsal fat pad just above the eyelid crease. CONCLUSIONS: Ultimately, our findings demonstrate the effectiveness of finite element analysis, grounded in membrane bending theory, in elucidating the dynamics of upper eyelid crease formation. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors   www.springer.com/00266 .

N,N'-[(2,3,5,6-Tetra-methyl-p-phenyl-ene)dimethyl-ene]bis-[2-chloro-N-(2-chloro-ethyl)ethanamine].

The title mol-ecule, C(20)H(32)Cl(4)N(2), lies on an inversion center. A weak intra-molecular C-H⋯N hydrogen bond may, in part, influence the conformation of the mol-ecule.