Spontaneous interblink time distributions in patients with Graves' orbitopathy and normal subjects

To determine the shape of spontaneous interblink time interval distributions obtained in a long observation period in normal subjects and patients with Graves' orbitopathy.

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.

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.

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.