Concurrent and face validity of a capsulorhexis simulation with respect to human patients.

A prototype version of the ImmersiveTouch® virtual reality simulator was applied to capsulorhexis, the creation of circular tear or "rhexis" in the lens capsule of the eye during cataract surgery. Virtual and live surgery scores by residents were compared. The same three metrics are used in each mode: circularity of the rhexis, duration of surgery (sec), and number of forceps grabs of the capsule per completed rhexis (fewer is better). The average simulator circularity score correlated closely with the average live score (P = 0.0002; N = 4), establishing "concurrent validity" for this metric. Individuals performed similarly to each other in both modes, as shown by the low standard deviations for average circularity (virtual 0.92 ± 0.04; live 0.88 ± 0.04). By contrast, the standard deviations are high for the other two metrics, capsulorhexis duration (virtual 96.91 ± 44.23 sec; live 94.42 ± 65.74 sec, N = 8) and number of forceps grabs (virtual 10.66 ± 4.81; live 10.31 ± 5.23, N = 8). Nevertheless, the simulator was able to demonstrate that the surgeons with wide variations in total duration and number of capsular grabs in 2 to 4 trials of simulated surgery also had similar variations in live surgery, so that the simulator retains some realism or "face validity."