Since optical zone centration is of such importance in refractive surgery, we have studied, with a computer-aided videopupillograph, the problem of identifying it in myopes. The findings of pupil centre shift as a function of pupil diameter and degree of myopia are reported in two groups of myopes (low and medium) and a control group. Results indicate that the amount and direction of decentration vary according to pupil diameter and degree of myopia. No generally valid instructions can be laid down and each case must be treated on its merits.