24-12-6 rule is applied for

Safe surgical exploration distances during orbitotomy Safe distances for the periorbital dissection from the intact outside rim of the adult orbit to vital interior structures are specified in millimeters. Generally an exploration depth of 25 mm along the lateral and inferior walls is regarded as safe. A 30 mm distance from the supraorbital rim and the anterior lacrimal crest are also considered safe exposure of the roof and the medial wall respectively. Along the medial wall, impoant landmarks are described as measurements from the anterior lacrimal crest : - 24 mm* to the anterior ethmoidal foramen - 36 mm* to the posterior ethmoidal foramen (12 mm from the anterior ethmoidal foramen) - 42 mm* to the optic canal (6 mm from the posterior ethmoidal foramen) * Mnemotechnic formula (rule of halves): 24-12-6.