Eric Matheron

Vertical phoria and postural control in upright stance in healthy young subjects

OBJECTIVEnTo test the quality of postural performance in quiet upright stance in healthy young adults with vertical heterophoria (VH) within the normal range and without VH (vertical orthophoria, VO).nnnMETHODSnTwenty-six subjects took part in this study. The postural stability was measured with a force platform while the subjects fixated a target at eye level in a straight ahead position, placed at either 40 or 200cm.nnnRESULTSnThe results indicated that the postural control was better for subjects with VO than subjects with VH. Particularly, there was an interaction between vertical phoria and distance: the subjects with VH showed greater instability than the subjects with VO at a far distance only. An additional study showed that the cancellation of VH with a prism improved postural stability.nnnCONCLUSIONSnThe quality of postural performance in quiet upright stance was lower in the subjects with VH. We speculate that VH, even when small in size, indicates a perturbation of the somatosensory/proprioceptive loops involved in postural control.nnnSIGNIFICANCEnVertical phoria could perhaps indicate the capacity of the central nervous system to integrate optimally proprioceptive cues.

Postural Control during the Stroop Test in Dyslexic and Non Dyslexic Teenagers

Postural control in quiet stance although simple still requires some cognitive resources; dual cognitive tasks influence further postural control. The present study examines whether or not dyslexic teenagers experience postural instability when performing a Stroop dual task for which their performances are known to be poor. Fifteen dyslexics and twelve non-dyslexics (14 to 17 years old) were recruited from the same school. They were asked to perform three tasks: (1) fixate a target, (2) perform an interference Stroop test (naming the colour or the word rather than reading the word), (3) performing flexibility Stroop task: the subject performed the interference task as in (2) except when the word was in a box, in which case he had to read the word. Postural performances were measured with a force platform. The results showed a main task effect on the variance of speed of body sway only: such variance was higher in the flexibility task than for the other two tasks. No group effect was found for any of the parameters of posture (surface, mediolateral and anteroposterior sway, variance of speed). Further wavelet analysis in the time-frequency domain revealed an increase in the spectral power of the medium frequency range believed to be related to cerebellum control; an accompanying increase in the cancellation time of the high frequency band related to reflexive loops occurred for non-dyslexics only. These effects occurred for the flexibility task and could be due to its high cognitive difficulty. Dyslexics displayed shorter cancellation time for the medium frequency band for all tasks, suggesting less efficient cerebellar control, perhaps of eye fixation and attention influencing body sway. We conclude that there is no evidence for a primary posture deficit in 15 year old teenagers who come from the general population and who were recruited in schools.

Effects of ocular dominance on the vertical vergence induced by a 2-diopter vertical prism during standing.

This study examined the eye movement responses to vertical disparity induced by a 2-diopter vertical prism base down while in standing position. Vertical vergence movements are known to be small requiring accurate measurement with the head stabilized, and was done with the EyeLink 2. The 2-diopter vertical prism, base down, was inserted in front of either the non-dominant eye (NDE) or dominant eye (DE) at 40 and 200 cm. The results showed that vertical vergence was stronger and excessive relative to the required value (i.e. 1.14 degrees ) when the prism was on the NDE for both distances, but more appropriate when the prism was on the DE. The results suggest that sensory disparity process and vertical vergence responses are modulated by eye dominance.

Active ocular vergence improves postural control in elderly as close viewing distance with or without a single cognitive task

Performance of the vestibular, visual, and somatosensory systems decreases with age, reducing the capacity of postural control, and increasing the risk of falling. The purpose of this study is to measure the effects of vision, active vergence eye movements, viewing distance/vergence angle and a simple cognitive task on postural control during an upright stance, in completely autonomous elderly individuals. Participated in the study, 23 elderly subjects (73.4 ± 6.8 years) who were enrolled in a center dedicated to the prevention of falling. Their body oscillations were measured with the DynaPort(®) device, with three accelerometers, placed at the lumbosacral level, near the center of mass. The conditions were the following: eyes open fixating on LED at 20 cm or 150 cm (vergence angle 17.0° and 2.3° respectively) with or without additional cognitive tasks (counting down from one hundred), performing active vergence by alternating the fixation between the far and the near LED (convergence and divergence), eyes closed after having fixated the far LED. The results showed that the postural stability significantly decreased when fixating on the LED at a far distance (weak convergence angle) with or without cognitive tasks; active convergence-divergence between the LEDs improved the postural stability while eye closure decreased it. The privilege of proximity (with increased convergence at near), previously established with foot posturography, is shown here to be valid for accelerometry with the center of mass in elderly. Another major result is the beneficial contribution of active vergence eye movements to better postural stability. The results bring new perspectives for the role of eye movement training to preserve postural control and autonomy in elderly.

Spherical Lenses and Prisms Lead to Postural Instability in Both Dyslexic and Non Dyslexic Adolescents

There is controversy as to whether dyslexic children present systematic postural deficiency. Clinicians use a combination of ophthalmic prisms and proprioceptive soles to improve postural performances. This study examines the effects of convergent prisms and spherical lenses on posture. Fourteen dyslexics (13–17 years-old) and 11 non dyslexics (13–16 years-old) participated in the study. Quiet stance posturography was performed with the TechnoConcept device while subjects fixated a target at eye-level from a distance of 1_m. Four conditions were run: normal viewing; viewing the target with spherical lenses of −1 diopter (ACCOM1) over each eye; viewing with −3 diopters over each eye (ACCOM3); viewing with a convergent prism of 8 diopters per eye. Relative to normal viewing, the −1 lenses increased the surface of body sway significantly whereas the −3 diopter lenses only resulted in a significant increase of antero-posterior body sway. Thus, adolescents would appear to cope more effectively with stronger conflicts rather than subtle ones. The prism condition resulted in a significant increase in both the surface and the antero-posterior body sway. Importantly, all of these effects were similar for the two groups. Wavelet analysis (time frequency domain) revealed high spectral power of antero-posterior sway for the prism condition in both groups. In the ACCOM3 condition, the spectral power of antero-posterior sway decreased for non dyslexics but increased for dyslexics suggesting that dyslexics encounter more difficulty with accommodation. The cancelling time for medium range frequency (believed to be controlled by the cerebellum), was shorter in dyslexics, suggesting fewer instances of optimal control. We conclude that dyslexics achieve similar postural performances albeit less efficiently. Prisms and lenses destabilize posture for all teenagers. Thus, contrary to adults, adolescents do not seem to use efferent, proprioceptive ocular motor signals to improve their posture, at least not immediately when confronted to convergence accommodation conflict.

A 1-Diopter Vertical Prism Induces a Decrease of Head Rotation: A Pilot Investigation

Clinical studies in non-specific chronic arthralgia and back pain seem to indicate an association between vertical heterophoria (VH – latent vertical retinal misalignment) and asymmetrical head rotation. Such clinical observations suggest a link between VH and head rotation, but this was never tested. The purpose of this study was to simulate a VH in healthy subjects and examine its influence on the amplitude of active head rotation during 3D motion capture in upright stance. Subjects were asked to rotate their head three times from the straight ahead position and then to the right, back to straight ahead, to the left, and back to the straight ahead again. Three randomized conditions were run: normal viewing, with a 1-diopter prism base down on the dominant eye, or the non-dominant eye. The most important finding is that the experimental VH whichever the eye with the prism induces a significant decrease in the mean angle of head rotation compared to the normal viewing condition. This decrease was significant for rotation to the left. We suggest that the prism-induced VH modifies the reference posture and thereby affects head rotation; further studies are needed to confirm this effect and to extend to other types of dynamic activities.

Des stimulations plantaires fines améliorent le contrôle postural orthostatique uniquement pour les sujets sans Épines Irritatives d’Appui Plantaire

Introduction L’objectif est d’evaluer l’effet de stimulations plantaires fines sur le controle postural lors de mouvements de vergence. Materiel et methode La stabilite de 36 sujets asymptomatiques (25,7xa0±xa03,6xa0ans) a ete enregistree par plate-forme de forces selon 3 conditionsxa0: sans stimulation plantaire, avec un insert de 3xa0mm d’epaisseur, medial (Medial Arch Support) ou lateral (Lateral Arch Support). Resultats Les resultats ont montre une diminution de la Surface et de la Variance de la Vitesse avec les stimulations, compare a la condition controle. L’analyse fractale montre une diminution du pourcentage des points non correles avec MAS. L’analyse par ondelettes des deplacements du CPP revele une augmentation du Temps d’Annulation dans la bande de frequences basses avec MAS. La position moyenne en Y du CPP est plus posterieure avec MAS et LAS. Enfin, lorsque les sujets sont classes en 2 groupes en fonction de leur QP (QPxa0=xa0Surface mousse /Surface sol dur ), un tiers d’entre eux se revelent etre porteurs d’Epines Irritatives d’Appui Plantaire (EIAP). Ces sujets font preuve d’une sensibilite nettement moindre aux stimulations plantaires, ne montrant plus de difference significative que sur leur critere positionnel (Y moyen). Conclusion Nous en concluons que des inserts plantaires specifiques, bien que tres fins, permettent d’ameliorer le controle postural (meilleure stabilite pour un cout energetique moindre) par enrichissement des afferences cutanees plantaires, uniquement en l’absence d’EIAP. Celles-ci empechent l’integration correcte de ces afferences.

Incidences d’un prisme vertical d’une dioptrie sur la rotation cervicale active dents serrées ou non : résultats préliminaires et perspectives cliniques

37 Incidences d’un prisme vertical d’une dioptrie sur la rotation cervicale active dents serrees ou non : resultats preliminaires et perspectives cliniques E. Matherona,b, Z. Kapoulaa a Groupe IRIS, centre d’etudes de la sensorimotricite (CESeM), CNRS/UMR 8194, service d’ophtalmologie-ORL-stomatologie, universite Paris Descartes, hopital Europeen Georges-Pompidou, Paris, France b Cabinet de kinesitherapie, Dijon, France