Tarsal thickness comparison between upper and lower eyelids

Background: The difference between the upper and the lower eyelids are still unknown. Objective: To compare the thickness of upper and lower tarsal plates in microscopic specimens. Methods: Central sagittal sections of 22 upper and lower eyelids on the same hemi-faces (12 right and 10 left) from 15 Japanese cadavers (8 males and 7 females), aged 38-88 years (average age: 70.5 years) were histologically examined. The specimens were fixed in 10% formalin and stained with the Masson’s trichrome. The thickest part of each specimen was measured on inspection. The statistical analyses were performed using the Student t-test to compare the thickness of the upper and lower tarsal plates. The Mann-Whitney U-test was used to examine the age differences: younger group (38-61-year-old) and elder group (73-88-year-old), sex, and laterality in each upper or lower eyelid. The significance level was set at 0.05. Results: The total upper and lower tarsal plate thickness showed a statistically significant difference, in which the lower tarsal plate was thicker than the upper (p=0.001). The differences in tarsal plate thickness by age (p=0.632 in upper, p=0.585 in lower), sex (p=0.844 in upper, p=0.375 in lower), and laterality (p=0.921 in upper, p=0.307 in lower) did not reach statistical significance. Conclusion: The lower tarsal plate thickness was thicker than the upper one, but no difference was shown in age, sex, and laterality between the upper and lower tarsal plates.