 40 eyes of 40 patients who had extraocular surgery under general anesthesia will be included in this prospective study. Cell density, Cell variatio, Hexagonality rate and pachymetry specular microscopy results at before surgery and 1 week and 1 month after surgery will be analyzed. O2 1 lmin with 50 air and N2O 1 lmin with 50 air will be applied to each group with flow rate 2 lmin totally, respectively. The duration of surgery will be recorded. 