 To study the dynamics of ocular autoregulation, it is necessary to introduce a step disturbance stimulus in ocular perfusion pressure and to record the responses of ocular blood flow continuously before and after this step disturbance. The investigators have employed a mechanical noninvasive technique to induce an ocular perfusion pressure step disturbance without drugs or changes in the concentration of vasoactive substances in the blood by using the thigh cuff technique inducing a small step decrease in ocular perfusion pressure. 