Blink frequency and duration during perimetry and their relationship to test-retest threshold variability

To describe different patterns of blinking in patients undergoing a visual field test and to establish whether the blink parameters are related to threshold variability.

Thirty-nine patients with diagnosed or suspected glaucoma were recruited to undertake a perimetric task twice. Blinks were detected with a video eye-tracker system that records at a sampling rate of 60 Hz. Blink frequency, duration, and episodes of microsleep (eye closures >500 ms) were analyzed, and correlated with test-retest threshold variability. The timing of blinks with respect to stimulus presentation was analyzed and the percentage of seen stimuli for all presentations (POS(overall)) and those overlapped with blinks (POS(overlapped)) were compared.

Blink frequency ranged from 0 to 58 per minute. A significant increase in blink frequency was observed in the second test (P < 0.001), whereas blink duration and microsleep episodes were not significantly different between the two tests. The relationship between test-retest threshold variability and all blink parameters was not significant. For suprathreshold stimulus presentations, blinks often occurred after presentation, whereas for subthreshold presentations, their timing was independent of stimulus timing. The difference between POS(overall) and POS(overlapped) was significant (P < 0.001), and a slight decrease in POS(overlapped) was observed with the increase of overlap duration.

A wide range of blink frequencies was observed during perimetric testing. Although no blink parameters showed significant influence on threshold variability, when the blinks overlapped with a stimulus presentation, the probability of seeing was reduced. For suprathreshold stimuli, blinks often occurred after the presentation, whereas for subthreshold presentations, there was no relationship to presentation time.