The surgical procedures of ETOCD. (a) The medical wall of optic canal was thinned by a microdrill. (b) The thinned medial wall of optic canal was removed by a microcurette. (c) The periorbita of the orbital apex and annulus of Zinn was split with a sharp 9# MVR knife. (d) Five to six small intermittent punctuated incisions were made to the optic nerve sheath.