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To evaluate the differences between Asian and Caucasian upper eyelid anatomy through cadaver dissection, histopathological study, and magnetic resonance imaging. Materials and Methods: Upper eyelids of 9 Korean and 5 Caucasian cadavers were dissected, and then were studied microscopically with hematoxylin-eosin, Masson trichrome, and elastin stains. Four healthy young Korean men were studied by dynamic high-resolution magnetic resonance imaging with regard to demonstration of upper eyelid structure. Results: More subcutaneous and suborbicularis fat, with a pretarsal fat component, is present in Asian eyelids. The Asian double eyelids showed an amount of fat intermediate between Asian single eyelids and Caucasian eyelids. Asian single eyelids showed fusion of the orbital septum to the levator aponeurosis below the superior tarsal border, while fusion is above the superior tarsal border in Caucasians. The preaponeurotic fat pad descends anteriorly to the tarsal plate in the Asian single eyelid, but not in the Caucasian eyelid. A pretarsal fat pad is identified in the Asian single eyelids. Conclusions: The causes of absent or lower crease in the Asian upper eyelid are as follows: (1) the orbital septum fuses to the levator aponeurosis at variable distances below the superior tarsal border; (2) preaponeurotic fat pad protusion and a thick subcutaneous fat layer prevent levator fibers from extending toward the skin near the superior tarsal border; and (3) the primary insertion of the levator aponeurosis into the orbicularis muscle and into the upper eyelid skin occurs closer to the eyelid margin in Asians. Structural differences relating to increased fat in the Asian upper eyelid include the presence of a pretarsal fat pad and a moderate fat increase in the double Asian eyelid.

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