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

Abstract

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. 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. 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 %). 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.