The Near Response: The Contributions of Kenji Ohtsuka, MD

Bedside Assessment of Vergence in Stroke Patients

BACKGROUND

Given the widely distributed network of midbrain, pontine, cerebellar, and cortical areas involved in the neural control of vergence, one might expect various vergence deficits in stroke patients. In this article, we investigated the localizing value of bedside vergence testing with respect to different supratentorial and infratentorial infarction locations.

METHODS

Three hundred five stroke patients and 50 age-matched controls were examined prospectively by means of bedside tests to assess slow and fast binocular (i.e., symmetrical) as well as slow and fast monocular (i.e., asymmetrical) convergence. Infarction locations, as identified on MRI, were correlated with vergence performance using multinomial logistic regression.

RESULTS

Vergence deteriorated with age in both stroke patients and healthy controls. Most infarction locations did not show significant associations with vergence parameters, apart from cases with parietal lobe lesions, which exhibited insufficient asymmetrical, slow and fast vergence for both the left and the right eye. Finally, patients with severe ischemic small vessel disease showed a slight but significant decrease in their fast binocular vergence performance.

CONCLUSIONS

There is only a limited localizing value of vergence deficits in stroke. Parietal lobe infarctions are more frequently associated with insufficient binocular and monocular vergence. Midbrain strokes were too few to draw final conclusions. However the most robust factor to emerge from our data is age. Older subjects show poor slow binocular as well as slow and fast monocular vergence. Extended white matter lesions are also correlated with deficient vergence ability suggesting a role for subcortical wide range connections in maintaining an intact vergence circuitry.

Impaired body balance control in adults with strabismus

Previous studies revealed that people with binocular vision disorders have poor postural stability. However, most of the research was performed only on children and under binocular viewing condition, that could negatively affect the results. The aim of the current study was to investigate the influence of extra-ocular proprioceptive signals on postural stability in young adults with binocular vision disorders. Moreover, additional mental task was introduced to detect any postural compensation which could possibly hide the real influence of afferent extra-ocular signals. 21 Subjects, aged 18-45 yrs, with horizontal strabismus, were qualified to binocular vision disorders (BVD) group. 41 subjects, aged 19-45 yrs, with no strabismus formed the normal binocular vision (NBV) group. Posturography data were collected in 2 separate parts: (1) quiet standing (Single-Task), and (2) performance of a mental task while standing (Dual-Task). Each part consisted of three 60-s viewing conditions, with: (1) dominant/fellow eye (DE), (2) non-dominant/strabismic eye (NDE), and with (3) both eyes closed (EC). Subjects were looking at X located at the distance of 150 cm. Generally, BVD group showed elevated body balance during quiet stance compared to NBV group. Interestingly, better stabilization in BVD group occurred under NDE viewing. Surprisingly, additional mental task improved the postural stability in BVD group almost to the level of NBV group. These findings emphasize the role of the eye-muscle signals in postural control and suggest that suitable vision therapy can be the appropriate way to improve body balance/motor functions in people with binocular vision disorders.