Purpose: To examine the post-aponeurotic space and to confirm and define the presence of a post-aponeurosis fat-pad.
Methods: Experimental anatomic study. Nineteen-orbits from 10 freeze-preserved, unembalmed cadavers of caucasian subjects. In 12 orbits of 7 cadavers, a transconjunctival dissection of the everted upper eyelid was undertaken. Müller's muscle (MM) and conjunctiva were dissected as a composite flap exposing the posterior surface of the aponeurosis (LA) and the commencement of the levator palpebrae superioris (LPS) muscle. Anatomical localisation was agreed by 2 senior surgeons and an anatomist (VM). In the remaining 7 orbits a 1cm central upper eyelid wedge-excision was paraffin-embedded and studied histologically.
Results: Nineteen upper-eyelids from 10 freeze-preserved, unembalmed caucasian cadavers (5-male, 5-female, mean age 80.9; range 67-91 years) were studied. Of 12 eyelids of 7 cadavers, dissected and macroscopically evaluated, a fat-pad was identified in the post-aponeurotic space of all eyelids. Of these, 8 (66%) were predominantly diffuse. The remainder, mixed diffuse-discrete. All 4 of the latter category appeared multi-lobular. The fat-pad was seen to lie predominantly centro-medially, overlying MM, extending superiorly beyond the LA to lie posterior to LPS. Of the 7 upper eyelid wedge-excisions examined microscopically, a fat-pad was identified in all post-aponeurotic spaces, lying between 2 distinct tracts of smooth muscle. The anterior smooth muscle tract was intimately related to the posterior aspect of the LA, in keeping with the posterior smooth muscle layer of the aponeurosis. The posterior smooth muscle tract was in keeping with MM, thicker than the anterior layer, multi-layered and in 6 of 7 eyelids, interspersed with fat.
Conclusions: We confirm and describe a distinct layer of fat in the post-aponeurotic space, consistently found between MM and the posterior smooth muscle layer of the aponeurosis. We refer to this as the post-aponeurosis fat-pad. These findings provide further anatomical detail for the surgeon undertaking blepharoptosis surgery, who may, in some cases, mistake the presence of fat in this space either for the pre-aponeurotic fat-pad, or for degenerative changes within MM that lies deep to it.