<prompt> The optic canal is a pa ofLesser wing of sphenoidGreater wing of sphenoidEthmoidPterygium  <response>: The optic nerve leaves the orbit is the optic canal to enter the cranial vault The optic canal is the most posterior landmark of the orbit. It measures 10mm in length The thin piece of bone separating the optic canal from the superior orbital fissure is the optic strut The optic strut and optic canal are a pa of the lesser wing of the sphenoid bone Fig - Foramina and bony landmarks of the sphenoid wings and pterygoid process. Reference : AK Khurana Comprehensive Ophthalmology, 6th edition, pg no. 310 