Postural stability changes during the prism adaptation test in patients with intermittent and constant exotropia

PURPOSE. Computerized static stabilometry is a clinical test in neurologic and muscular diseases to assess postural stability or body sway in a quantitative manner. The purpose of this study was to examine whether postural stability would change in the process of the prism adaptation test in patients with intermittent and constant exotropia. METHODS. Postural stability was measured before the prism adaptation test and immediately, 15 minutes, and 60 minutes after the prism adaptation test by computerized static stabilometry in 17 consecutive adult patients with exotropia, including 10 patients with intermittent exotropia and seven with constant exotropia. Stabilometric parameters were compared between patients with intermittent and those with constant exotropia for 60 minutes by repeated-measures analysis of variance as statistical analysis. RESULTS. The Romberg quotients for the root mean square areas of the sway path (cm ²), the area in the condition of the patients' eyes open, divided by that in the condition of the patients' eyes closed, increased significantly in the time course of the prism adaptation test and returned to the pretest level in patients with intermittent exotropia and in patients with constant exotropia (P = 0.0173). No significant difference in the Romberg quotients\ was noted between the patients with intermittent exotropia and those with constant exotropia. CONCLUSIONS. Postural instability became more pronounced by the prism adaptation test in the patients with exotropia. Binocular visual and motor perceptional changes induced by the prism adaptation test could lead to postural instability, with adaptation taking place 60 minutes after the start of the test.