Postural sway during retinal image stabilisation

Light finger contact concurrently reduces postural sway and enhances signal detection performance in children with developmental coordination disorder

The current study examined the effects of light finger touch on postural sway and signal detection performance in children with developmental coordination disorder (DCD). Children with DCD (n=30; 18 boys, 12 girls; age=11.87 ± 0.48 years) and typically developing children (n=30; 14 boys, 16 girls; age=11.73 ± 0.52 years) were recruited from schools in Pintung County, Taiwan. Participants completed a signal detection task under no finger touch (NT) and light finger touch (LT) conditions, while postural sway in both anteroposterior (AP) and mediolateral (ML) axes was recorded. In both conditions, children with DCD exhibited significantly higher levels of postural sway (p<0.05) and lower signal detection performances (p<0.05) than TDC. Additionally, both groups significantly reduced postural sway (p<0.05) and enhanced signal detection performance (p<0.05) when engaged in light finger touch compared with no finger touch. While the effect of LT on postural sway was greater among TDC relative to children with DCD (p<0.05), the effect of LT on signal detection was greater in children with DCD compared with TDC (p<0.05). These results suggest that light finger touch is effective in concurrently reducing postural sway and enhancing signal detection in both groups.

Postural stability in primary open angle glaucoma

BACKGROUND

This study evaluated the visual contribution to postural steadiness in primary open angle glaucoma (POAG), in correlation with the mean deviation (MD) measured through conventional perimetry, and with the Advanced Glaucoma Intervention Study (AGIS) score, which quantifies the extent of losses in the visual field.

METHODS

In 35 POAG patients and 21 age-matched normal subjects, the sway of the centre of pressure of the feet, on a firm or foam support, was recorded. The subjects stood on a force-plate with eyes closed, or with one or two eyes open.

RESULTS

For all subjects, the sway velocity was lower with vision than without vision, indicating the existence of a visual contribution to posture at all stages of glaucoma. This contribution was significantly lower for POAG patients than for normals in monocular and binocular vision, and decreased with the MD, or as the AGIS score increased. Among the maximum, minimum and average values of the two monocular MD, the MD of the worse eye presented the most significant negative correlation with the visual contribution to posture. The somatosensory contribution to postural steadiness was larger in POAG patients, as compared to normals, in monocular or binocular vision.

CONCLUSION

Primary open angle glaucoma induces a deficit in the visual contribution to postural steadiness, which should be taken into account for the prevention of falls.

Examination and refractive management of patients with nystagmus

Patients with nystagmus present unique challenges to the ophthalmologist. These patients can be difficult to examine and refract. Treatment options to improve vision or reduce disturbing visual symptoms are limited, which is disappointing to the patient and frustrating to the clinician. This paper will provide the clinician with one method of clinically organizing nystagmus, describe the patients who may benefit from optical treatments, and discuss the methodology used in their implementation. Techniques that will be discussed include patient examination and objective and subjective refraction. Optical treatments discussed include spectacles, prisms, contact lenses, and retinal image stabilization.

Lateral dynamic balance reactions to circular translation of the visual field

Lateral sway of subjects in spontaneous dynamic balance conditions on a seesaw platform was measured during a visual stimulation monocularly produced by a rotating glass covered with a prism membrane. Prism rotation induced the perception of a circular translation of the whole visual field and an ocular pursuit movement. Therefore, the retinal slip that occurs in normal pursuit was cancelled. Strong stereotyped postural reactions were observed in a direction that depended upon both the vertical visual field deviation and the eye stimulated: upper position of the right visual field induced a leftward sway resulting from an extension of the right hemibody; symmetrical reactions occurred for the left stimulation. The results suggest that the postural reactions recorded depend on the isolated oculomotor activity and, in addition, on retinal afferences corresponding to the temporal crescent of the stimulated side, which orientates the postural reaction on the homolateral lower limb muscles.

Relationship between head sway and center of foot pressure sway

We investigated the correlation between body sway and head sway in 64 healthy subjects who stood on a force-measuring platform. Each subject wore a helmet attached to a cephalograph and was asked to stand as still as possible on a platform with his feet close together for 60 sec. Subjects were asked to do this three times with their eyes closed and three times with their eyes open. We selected the test with the minimum sway for computer analysis of the sway path, sway area, ratio of anteroposterior/lateral components, sway velocity in each direction, averaged divisional frequency, and Romberg quotient. The movement of the head was significantly correlated with the center of foot pressure (COF) for the sway path, sway area, sway velocity, averaged divisional frequency, and the Romberg quotient. Our findings suggest that COF sway can be used instead of head sway to assess those five parameters.

Changes with aging in head and center of foot pressure sway in children

To quantitate the development of equilibrium in children, we investigated movements of the head and of the center of foot pressure (COF) in standing subjects, using a cephalograph, a force measuring platform, and a technical computer. We studied 126 subjects, 105 healthy children, aged 4-18 years, and 21 adults, aged 20-28 years. Each subject stood with their feet together on a platform for 60 s each with eyes open or closed. The area and total length of head and COF movements decreased with increasing age, and were significantly greater in children under 12 years than in adults. The ratio of the lengths of head to COF movements was significantly larger in children under 9 years than in adults. The ratio of the anteroposterior to lateral movement of COF was also larger in children under 9 years. These observations suggested that body sway in children was not only larger than that in adults, but different in nature.

Visual destabilisation of posture in normal subjects

A new and simple method of assessing reliance on vision for postural control was evaluated in 41 normal subjects. Left-right reversal of peripheral vision induced by a head-mounted mirror device caused an initial dramatic instability in approximately half the subjects, when standing on foam to reduce the value of proprioception. Lateral reversal of central vision by means of a prism device evoked similar responses. Sensitivity to vision reversal was significantly correlated with motion sickness susceptibility. Despite some rapid habituation (partially retained over several weeks) sway remained as great as with eye closure in the anterior-posterior as well as lateral direction, indicating complete suppression of the visual input. Balancing with vision reversal caused a selective decrement in performance of a visuo-spatial memory task, suggesting that coping with misleading visual input may place continuous demands on cortical spatial processing.