Spontaneous eyeblink activity under different conditions of gaze (eye position) and visual glare

Purpose: To further evaluate the spontaneous eyeblink rate (SEBR) of healthy adult human subjects according to direction of gaze, especially in the presence of bright light reflective glare. Methods: On 32 subjects aged between 18 and 24 years, separate video recordings of 5 min duration were made with different conditions of gaze (horizontal, slightly upwards or slightly downwards) under normal lighting or a distant lighting glare source. Results: The SEBR in primary eye gaze under normal lighting was 11.7 +/− 0.9 eyeblinks/min with a coefficient of variation (COV) of 20.5 %. A non-significant decrease in SEBR was noted with downward gaze, but a slight significant increase with upward gaze in both SEBR (to 13.0 +/− 1.1 eyeblinks/min) and COV (average 26.1 %). In the presence of glare, SEBR in primary eye gaze increased significantly (p < 0.001) to 14.4 +/− 1.3 eyeblinks/min, with an obvious time-related progressive increase (p < 0.001). On upward gaze in the presence of a glare stimulus, SEBR progressively increased even further (average 15.0 +/− 2.4 eyeblinks/min; p < 0.001), as did the COV (to 29.2 %). Conclusions: The results indicate that spontaneous eyeblink activity in silence can be affected by the presence of a glare light source, especially if the subjects are looking slightly upwards. This scenario should be avoided, if at all possible, in assessments of spontaneous eyeblink activity.