Stroke is the leading cause of disability in the United States and, according to the Centers for Disease Control, affects approximately 795,000 people per year. Upper limb motor impairment is a sequela in 80% of patients. Although these deficits affect independent function of the limb, recent evidence suggests that functional dependencies of function between the eye and hand may also be impaired, reflecting dyscoordination.1,2 As the dynamics between visual guidance and manual motor control are disturbed, patients may experience subclinical impairments, amplifying functional loss. Although current guidelines have centered on research developments that focus on limb impairment, a fundamental shift is occurring as studies begin to investigate the visual demands for coordinated control of the eyes and limbs.1,2
WHY IS THERE A PARADIGM SHIFT?
A critical element of neurological function is eye-hand coordination: the integrated control of ocular and manual motor systems to optimize functional interaction with a spatial object. Eye-hand coordination includes visually guided actions that are simple and those that are complex, for example, reaching and grasping a cup on the table or deftly manipulating the flaps of a cereal box to ensure the tab stays tucked. Many purposeful tasks are contingent upon the visual guidance afforded by eye movements, which are normally both temporally and spatially coupled to hand movements.1,2 Gaze control is an essential component of the visual guidance required for optimal performance during activities of daily living.1 Although these concepts are well accepted, there is a fundamental gap in the knowledge base regarding how stroke deficits affect the coordinative relationships between eye control and limb control.
Do post-stroke individuals experience eye-hand dyscoordination and/or related planning deficits?
There is strong evidence to suggest that stroke patients experience dyscoordination, in that the normal spatial and temporal relationships between eye and hand movements during tasks that require coordination are impaired, despite intact visual function. These eye-hand relationships may need to be specifically targeted during assessments and subsequently during neurorehabilitation.
WHY IS THIS RELEVANT TO PHYSIATRY?
Although a wide-ranging spectrum of impairment complicates stroke, assessment and management are heavily weighted toward motor deficits and intensive motor rehabilitation. However, improvements in motor ability do not ensure tangible gains in functional performance. Recently, it seems critical that targeted diagnostics and therapeutics be focused on visuomotor control post-stroke, above and beyond conventional rehabilitation.
A number of recent studies investigating eye-hand coordination post-stroke have revealed synchronization errors between ocular and manual motor systems during visually guided tasks, ultimately diminishing task performance. The latency or the onsets of eye and hand movements in both less- and more-affected hands were temporally decoupled; that is, the eye movements of stroke participants were mistimed relative to hand movement.1 In between the mistimed eye and the hand movement, stroke patients made multiple saccades per reach as opposed to a single saccade, used by most of the healthy controls.1 Despite the additional sensory information provided by these additional fixations and longer reach durations, which provided an extended opportunity to capitalize on feedback, spatial errors increased in both less- and more-affected hands.1,2
Relatedly, Singh et al.1 assessed visually guided function in chronic stroke through a modified trail making task and showed that not only did stroke patients make additional saccades but also revealed that these saccades, when executed during reaching, amplified reach impairment. These findings suggest that a visual search impairment may interfere with reach planning1; these results are consistent with the observation of additional, apparently non–goal-oriented saccadic eye movements by Rizzo et al.2 during eye-hand coordination.
WHAT IS THE IMPACT OF THESE FINDINGS ON PHYSIATRIC CLINICAL PRACTICE?
Physiatry plays a critical role in post-stroke care. Although visual and motor impairments may independently contribute to post-stroke deficits, resulting in various degrees of difficulty during a visual or manual task, dyscoordination of eye and hand movements may result in a compound impairment. These timing errors may result from an impaired limb that constrains the synchronization demands of coordinated function. Within rehabilitation, one must characterize ocular motor control, skeletal motor control, and coordination between effectors, all of which could lead to functional deficits. Recent findings suggest that timing errors between eye and hand post-stroke may require targeted ocular-manual motor assessments and integrated visuomotor interventions.1,2 Physiatrists should be aware of emerging trends and integrate best practices into a contemporary evidence base that supports optimized recovery in a comprehensive rehabilitation program.
WHAT QUESTIONS REMAIN OUTSTANDING?
More research is needed to further characterize eye-hand coupling in naturalistic tasks, particularly those surrounding reach-to-grasp, object manipulation, and tool use. In addition, studying novel rehabilitation interventions that target visuomotor integration may yield insight into eye-hand dyscoordination, stroke circuitry, and stroke recovery.
1. Singh T, Perry CM, Fritz SL, et al.: Eye
movements interfere with limb motor control in stroke survivors. Neurorehabil Neural Repair
2. Rizzo J-R, Fung JK, Hosseini M, et al.: Eye
control deficits coupled to hand
control deficits: eye
incoordination in chronic cerebral injury. Front Neurol