This is a study to focus on the feasibility of using a monitor which may signal loss of visual function intraoperatively.

The degree of a relative afferent pupillary defect (RAPD) has been correlated with the severity of an eye injury and has been shown to have prognostic significance as an indicator of retinal ischemia. Therefore light flashed evoked pupillometry (LFEP) may serve as a useful indicator of visual function. LFEP's are not known to be sensitive to anesthetics. We will measure LFEP's using different anesthetic techniques to see if there are measurable differences in the latency, amplitude and constriction velocity of the pupillary reflex. Prior to induction of anesthesia, pupillometer readings will be taken in the supine position in both eyes. The patient will be anesthetised using a standard induction technique. For maintenance of anesthesia a remifentanil infusion will be administered and supplemented by either propofol infusion (at 120 and 160 mcg/kg/min)or sevoflurane (at 1.5 and 2.5% end-tidal in random sequence. The patients will receive muscle relaxants as needed. Pupillometry readings will be taken in both eyes after induction, after steady maintenance has been achieved and every 10 minutes for 30 minutes at each drug dose.

Inclusion Criteria:

• planned orthopedic surgery on the lower extremities and positioned on the back

Exclusion Criteria:

• recent bout of conjunctivitis or pink eye
• condition which inhibits the normal pupillary function of my eye

subjects undergoing orthopedic surgery in the supine position