Further Analysis of the Human Spontaneous Eye Blink Rate by a Cluster Analysis-Based Approach to Categorize Individuals With ‘Normal’ Versus ‘Frequent’ Eye Blink Activity

Abstract

To further analyze the possible causes of variability in spontaneous eye blink activity in apparently healthy humans. One hundred men, aged between 23 and 57 years and with no significant eye disease, were questioned on the number of ocular symptoms they experienced (one, two, three, and so forth). Five-minute video recordings were made of the eyes in primary gaze and in silence between 11:00 and 17:00 hours. The spontaneous eye blink rate (SEBR) and palpebral aperture features were assessed from the video recordings. The central corneal threshold touch sensitivity was then assessed with a Cochet-Bonnet aesthesiometer. The average SEBR was 13.8 +/- 9.7 blinks per minute (range, 2.8-48 blinks per minute), but the distribution was heterogeneous and skewed to higher values. The SEBR was not obviously dependent on the time of day that the recordings were made, on the number of mild symptoms that the subjects reported, or on the central corneal sensitivity (P> or =0.6). Analysis of SEBR in relation to age showed a possible weak association (P=0.082, r = 0.175), but SEBR showed absolutely no correlation with palpebral aperture height (P=0.546). A hierarchic cluster analysis clearly resolved the distribution of SEBR values into two distinct groups (P<0.001, F ratio = 222). Spontaneous eye blink activity can be rather different between healthy individuals, even under a single experimental condition. These differences do not appear to be caused by the time of day, mild symptoms, corneal sensitivity, age, or palpebral aperture features. In line with previous metaanalyses, it is therefore proposed that individuals could be grouped as to whether they have "normal" eye blink activity or be classified as having "frequent" eye blink activity. The latter group would include those who had an SEBR greater than 20 blinks per minute when assessed in primary eye gaze and in silence.