Effet d'un prisme vertical de deux dioptries sur la stabilité posturale

Clinical trials have shown the relationship between vertical heterophoria (VH), chronic pain and quality of postural control. The aim of this study was to simulate a vertical heterophoria and observe its influence on postural stability while in the upright stance. Fifteen healthy, young, normophoric adults (25.6 ± 3 yrs) without otoneurological or ophthalmological problems were studied. Postural stability was assessed using a force platform in the following conditions: normal vision (NV); with a 2-diopter vertical prism, lower base, on the dominant eye (PDE); with a prism on the non-dominant eye (PNDE). In all the conditions, both eyes were open. All the measurements were recorded twice, with the subject fixing a target at distance (200 cm) and close up (40 cm). In the NODP condition the results show, whatever the distance, a significant increase in the standard deviation of anterior posterior oscillations compared with the NV condition. The PDE condition increases the postural stability only with long distance sight (decrease in the surface and in the standard deviation of the lateral oscillations). The deleterious effect, in the upright stance, on the anterior posterior stability for the PNDE conditions, is attributed to a maladjusted oculomotor response. The improvement in postural stability in NODP condition in long sight could be due to the oculomotor response reducing the vertical disparity and modifying the dynamic and tonic activity of the oculomotor muscles compared with the long-sight NV condition. We therefore conclude that the VH induced experimentally can influence postural control. Moreover, the clinical use of vertical prisms even of low strength should be considered with caution because they could have complex, positive or negative effects, depending on the eye implied and the distance of the target.