Keros Classification Classifies the depth of the olfactory fossa defined as follows: Keros I: 1-3mm Keros II: 3-7mm Keros III: 7-16mm Keros P. [On the practical value of differences in the level of the lamina cribrosa of the ethmoid]. Z Laryngol Rhinol Otol. 1962;41:809-13. Contributor: Alex Goel, MD