Purpose. To further assess the spontaneous eyeblink rate (SEBR) in primary gaze in young adults to further define the causes of variance in this activity. Methods. Nonconcealed video recordings were made of 61 white adults (30 males), aged 18 to 28 years, while silently directing their gaze to a 2-m-distant, 35-mm-high target under 350 lux illumination. An event marker was used to trace the video recordings in real time. Results. The overall SEBR was 10.3 +/- 3.1 eyeblinks/min (+/- SD) and the inter-eyeblink interval (IEBI) was 6.4 +/- 2.4 s, with no difference being detected between men and women (p > 0.1). There was no evidence of substantial time-dependent change in SEBR during the 5-min recording period. As assessed on a single occasion, it was noted that the subjects could display one of three patterns of eyeblink activity, namely irregular J-type, or symmetrical. Both the SEBR and IEBI values were statistically different (p less than or equal to 0.05) for the three patterns, with the highest SEBR values (12.3 +/- 2.4 eyeblinks/min) and lowest IEBI values (5.1 +/- 1.3 s) being observed for those with a symmetrical eyeblink pattern. Conclusions. Different patterns of spontaneous eyeblink activity can result in differences in the SEBR and IEBI values. It is proposed that the pattern of spontaneous eyeblink activity where there are similar intervals between each eyeblink event should be referred to as a "normal" (rather than symmetrical) pattern and should be considered as the normal eyeblink activity, both from a physiological and statistical perspective.
