Extent of Inferior Dissection Below the Orbital Rim
When freeing the premaxillary and prezygomatic spaces during subperiosteal dissection, extend the dissection to the orbital floor itself, which typically lies approximately 7-8 mm below the inferior orbital rim, ensuring complete release of the periorbita from the inferior orbital fissure when accessing the inferolateral orbital apex. 1, 2
Anatomical Landmarks and Dissection Depth
The inferior extent of dissection depends on your surgical goals and anatomical considerations:
For standard orbital floor access via preseptal transconjunctival approach: The subperiosteal dissection should continue from the inferior orbital rim toward the orbital floor, with the periosteum incised and reflected at the rim level 2
For enhanced access to the inferolateral orbital apex: Release of the inferior orbital fissure provides an additional 10.93 ± 2.10 mm of posterior access, requiring dissection of the plane between periorbita and Müller's muscle overlying the entire length of the inferior orbital fissure 1
Anatomical reference point: The infraorbital foramen typically lies 6.71 ± 1.11 mm below the infraorbital rim, and the infraorbital nerve may descend up to 11.9 ± 2.5 mm below the rim in anatomical variants 3, 4
Critical Surgical Considerations
Nerve Protection
The infraorbital nerve requires careful attention: In 12.5% of cases, the nerve descends into the maxillary sinus lumen, and this increases to 27.7% when an infraorbital ethmoid cell is present 4
When the nerve descends, it traverses the sinus lumen diagonally for a mean length of 15.4 ± 3.1 mm and is located 8.6 ± 2.9 mm below the sinus roof 4
Dissection Technique
The preseptal approach provides a bloodless anatomical plane: Dissect between the preseptal cranial conjunctival flap (covered by orbital septum) and the caudal conjunctival flap (covered by orbicularis muscle fascia) toward the inferior orbital rim 2
Maintain subperiosteal dissection: This plane protects neurovascular structures and provides safe access to the entire orbital floor 2
Common Pitfalls to Avoid
Inadequate inferior dissection: Leaving residual bone at the junction of the orbital rim and floor creates "blind spots" that hinder complete membrane detachment and increase perforation risk 5
Nerve injury from anatomical variants: Failure to recognize descended infraorbital nerves, particularly in the presence of infraorbital ethmoid cells, increases risk of iatrogenic injury 4
Insufficient lateral extension: The dissection must extend laterally to adequately free the prezygomatic space, as the infraorbital foramen is typically located 23.8 ± 3.1 mm medial to the zygomaticofrontal suture 6