Disorders of head-eye coordination.

Head-eye coordination subserves the rapid transference of gaze and between gaze shifts stabilizes fixation on stationary or smoothly moving targets. The coordination involves various combinations of the components of head movement, saccadic eye movements and visual and vestibular slow phase eye movement whose fine tuning may be adjusted, to an extent currently debated, by higher order mechanisms. Disorders of head-eye coordination may result in loss of acuity when slow phases are impaired or difficulty with reorientation if there is difficulty with saccades or head movement. Pathophysiology in the brain stem affecting individual components of eye movement may often be identified with success, particularly for the horizontal system, but the organization of other functions, notably pursuit suppression and vertical movements, are little understood. Similarly little is known about the disorders of the overall pattern of coordination--'gaze types'--including the apraxias, which have been attributed to cortical, basal ganglia or even cerebellar dysfunction and are reported in an almost bewildering variety of diseases. The development of coordination in infancy is a rich field in which there have been few studies with adequate observational techniques. The differentiation between congenital disorders whose severity may subsequently wax or wane, variants on normal development and acquired disorders poses a clinical problem which could largely be resolved with adequate recording techniques. For the future there is the tantalizing promise that once the principles of coordination are understood, we can move on to the more intriguing questions of how a certain 'toss of the head' and 'look in the eye' not only transfer gaze but can also be so meaningful.