Age-related changes in human blinks. Passive and active changes in eyelid kinematics.

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Abstract

PURPOSE: The authors analyzed eyelid kinematics in normal aging subjects to test the hypothesis that eyelid movements exhibit age-related changes and that blink disorders prevalent among the elderly, in turn, represent an outcome of normal aging processes. METHODS: The electromagnetic search coil technique was used to study blinks in normal human subjects for each decade from 40 to 89 years. Blink metrics (amplitude, peak velocity, and duration), main sequence relationships, and conjugacy were assessed. RESULTS: Mean amplitude and peak velocity of blinks decreased with age for spontaneous blinks and, to a lesser extent, for voluntary blinks. Some but not all, of this decline could be attributed to a peripheral phenomenon, narrowed palpebral fissure width. The spontaneous blink down phase main sequence slope also declined with age. By contrast, blink rate and the coordination of movements of the two eyelids--blink conjugacy--exhibited no change. CONCLUSIONS: These data demonstrate that disorders of blink systems typically seen in persons 50 years of age or older occur on a background of normal age-dependent changes in eyelid kinematics. Alterations in main sequence slope imply the operation of central adaptive systems during aging. Reduction in main sequence slope is interpreted as a reduction in aggregate orbicularis oculi motoneuron activity. Such a central neurologic adjustment in the motor output of blink systems may serve to compensate for an age-related increase in blink reflex excitability. Compensatory reduction in the main sequence relationship may offset a potentially hyperexcitable blink reflex, thereby reducing the likelihood of disorders such as blepharospasm. The authors conclude that although there are changes in the kinematics of blinking with age, such changes do not necessarily predispose an aging population to eyelid motility disorders.