Comparison of upper eyelid skin thickness at 5 mm and 12 mm from the eyelid margin in Asian

Background: The upper eyelid skin is considered to be gradually thicker going upward. However, the skin thickness can vary among individuals. This has not yet been confirmed. Objective: To microscopically examine the skin thickness at 5 and 12 mm from the eyelid margin in Asian individuals. Methods: A histological evaluation was conducted on 20 upper eyelids (10 right and 10 left) from 14 Japanese cadavers (age range: 36-97 years old, average: 68.9). The specimens were fixed in 10% formalin and stained with Masson’s trichrome. Skin thickness was measured at 5 and 12 mm from the eyelid margin and compared. The eyelid margin was defined as the anterior edge of the upper tarsal plate. Statistical analyses were conducted using the Mann-Whitney U-test, with a significance level set at 0.05. Results: The skin at 5 and 12 mm from the upper eyelid margin showed statistically similar thickness (p=0.064). However, the skin thickness distribution was categorized into four distinct types. The first type was much thicker at 12 mm (over 2 times thicker), observed in four eyelids from three cases. The second type showed moderately thicker skin at 12 mm (between 1.5 and 2 times thicker), found in three eyelids in three cases. The next type exhibited similar thickness at both 5 and 12 mm. It was divided into two subgroups: one coherently thin at both positions (less than 0.5 mm, four eyelids from three cases), and the other demonstrated consistently thick skin at both positions (over 0.5 mm, nine eyelids from eight cases). Conclusion: The upper eyelid skin thickness was statistically similar at 5 and 12 mm from the eyelid margin, but four distinct skin thickness types were identified based on the upward distribution. Level of Evidence: Level II