Purpose: This study was designed to examine the distance from the posterior lacrimal crest to the posterior margin of the Horner's muscle origin (the PLC-HMO distance), considering their complex anatomical relationship.
Methods: Eight macroscopic specimens from 8 Japanese cadavers and 7 microscopic specimens from 7 Japanese cadavers, fixed in 10% buffered formalin, were analyzed. Macroscopically, the PLC-HMO distance was measured at 2 mm superior to the most posterior point of the muscle origin (Group A), directly at the most posterior point (Group B) and 2 mm inferior to the most posterior point (Group C). Microscopically, the PLC-HMO distance was measured in axial sections at 1 mm above the upper eyelid margin (Group 1), 1 mm below the lower eyelid margin (Group 2), and 3 mm below the lower eyelid margin (Group 3).
Results: In the macroscopic study, the average PLC-HMO distance was 2.94, 2.57, and 2.05 mm for Groups A, B and C, respectively. The distance for Group C was significantly smaller than that of Group A (p = 0.006). In the microscopic study, the average PLC-HMO distance was 3.62, 3.74, and 3.14 mm for Groups 1, 2 and 3, respectively (no significant difference).
Conclusions: The PLC-HMO distance was approximately 2-4 mm with some specimens showing a smaller distance inferiorly.