Purpose: To analyse the spontaneous eyeblink rate (SEBR) and inter-eyeblink intervals (IEBI) of normal volunteers before and during video display terminal (VDT) use.
Methods: The SEBR of 51 normal volunteers was measured by counting the absence of the corneal reflex using a computer-based video analysis system. Only complete eyeblinks were recorded within 10 min under three different conditions: during a conversation, during VDT use without corneal anaesthesia, and during VDT use with corneal anaesthesia. The IEBI (in seconds) were determined to study individual time-dependent changes of SEBR.
Results: In comparison with SEBR during conversation (mean 15.54 eyeblinks/min, standard deviation +/-13.74 eyeblinks/min) the SEBR decreased significantly during VDT use without corneal anaesthesia (5.34 +/- 4.53 eyeblinks/min). Corneal anaesthesia further significantly reduced SEBR (2.78 +/- 2.77 eyeblinks/min). The SEBR was characterized by marked interindividual variability, ranging between 11 and 664 eyeblinks/10 min during conversation, between 4 and 189 eyeblinks during VDT use without corneal anaesthesia and between 1 and 119 eyeblinks at VDT use with corneal anaesthesia. No significant correlation between SEBR (during conversation or during VDT use) and quality (break-up time) or quantity (Schirmer I test, Jones test) of the tear film could be detected. Evaluation of the IEBI revealed three different types of eyeblink pattern during VDT use without corneal anaesthesia. Type 1 was characterized by a very low SEBR (0-2 eyeblinks/min) and relatively homogeneous distribution of eyeblinks, type 2 showed a moderate SEBR (1.2-8.5 eyeblinks/min) including three further subtypes. Type 3 was characterized by a high SEBR (6.8-18.9 eyeblinks/min) of regular or irregular pattern.
Conclusions: VDT use is associated with a profound decrease of the SEBR in healthy subjects. There are marked interindividual differences in SEBR and no correlation between the SEBR and ocular tear film parameters in normal eyes. The SEBR is further reduced by corneal anaesthesia. The presence of different patterns of eyeblinking may be related to various exogenous and endogenous factors and may lead to a better understanding of ocular reactions during VDT use.