Purpose: To determine the shape of spontaneous interblink time interval distributions obtained in a long observation period in normal subjects and patients with Graves' orbitopathy.
Methods: The magnetic search coil technique was used to register the spontaneous blinking activity during 1 hour of video observation of two groups of 10 subjects each (normal controls aged 27-61 years, mean ± SD = 46.0 ± 13.6; patients with Graves' orbitopathy aged 33-61 years, mean ± SD = 46.7 ± 8.9). The spontaneous blink rate of each subject was calculated for the entire period of observation and for 56 five-minute bins. Histograms of the interblink time interval were plotted for each measurement of blink rate.
Results: Neither the overall mean blink rate (controls, 19.8 ± 4.9; Graves', 17.6 ± 5.4) nor the interblink time (controls, 5.2 ± 3.1, Graves', 7.9 ± 3.5) differed between the two groups. There was a large variation of both measurements when the 5-minute bins were considered. The interblink time distribution of all subjects was highly positively skewed when the 1-hour period was measured. A significant number of the 5-minute bin distributions deviated from the overall pattern and became symmetric.
Conclusions: The normal blinking process is characterized by highly positively skewed interblink time distributions. This result means that most blinks have a short time interval, and occasionally a small number of blinks have long time intervals. The different patterns of distribution described in the early literature probably represent artifacts because of the small samples analyzed.