This study involves evaluation of the surgical limits of transantral orbital apex decompression (as described by Ogura) by performing the operation on 17 cadaveric half-heads. Measurements were then made of the proximity of bone removal to several vital structures including the optic nerve, carotid artery siphon, cavernous sinus, and frontal lobe dura. Entrance into the sphenoid sinus was found to be routine. Adequate decompression requires maximum removal of bone at the orbital apex and incision of the periorbita without damage to the adjacent vital structures. This requires; 1. knowledge of ethmoid and sphenoid sinus anatomy and recognition of anatomic variations, 2. removal of bone under direct visualization, and 3. incisions of the periorbita be made most posteriorly first to prevent prolapse of orbital fat anteriorly which obscures vision of the critical orbital apex periorbita.