Menstrual cycle effects on postural stability but not optokinetic function.

We investigated the effects of the menstrual cycle on visual-vestibular interaction by measuring optokinetic function and postural stability at different phases of the cycle. Menstrual cycle phase had no significant effect on gaze-holding, optokinetic nystagmus slow phase velocity, amplitude or frequency, circularvection latency or optokinetic afternystagmus frequency, amplitude or duration. While menstrual cycle phase had no significant effect on anterior-posterior sway, it did significantly affect lateral sway (P<0.001), with sway on day 5 significantly greater than on days 12 and 21 (P<0.05 and 0.01, respectively), and sway on day 25 significantly greater than that on day 21 (P<0.05).