Quantitative analysis of eyelid movement metrics reveals the highly stereotyped nature of monkey blinks

Blink movement metrics were studied in three alert cynomolgus monkeys using electromagnetic search coils attached to the eyelids bilaterally. Monkey blinks averaged approximately 24 degrees. Down-phase peak velocities were approximately twice those of the corresponding up phases. Most blinks were symmetrical with close temporal linkage of onset and offset between the two eyelids. Monkey blinks exhibited higher peak velocities and shorter durations than have been previously described for similar amplitude movements in humans. Peak velocity vs. amplitude plots were linear and non-saturating within a 45 degrees range for both up and down phases. The relationship between blink peak velocity and average velocity was linear with a slope of approximately 2.0. These values were very similar to those obtained by others, not only for blinks, but also for saccadic eye and ballistic limb movements. Down-phase amplitude-duration behavior could be best described by a linear function with slope < 0.7, while amplitude-duration slope of up phases was best described by a second-order polynomial. Unlike saccadic eye movements, larger amplitude blinks are obtained primarily via increases in peak velocity rather than through extension of blink duration. These data provide mathematical descriptions of monkey blink behavior that indicate the stereotypical nature of blinks. This will serve as a normative data base with which to better understand the neural processing that goes into blinks and will allow the assessment of eyelid movement disorders and evaluation of potential treatments of these disorders.