Blink Rate Measured In Situ Decreases While Reading From Printed Text or Digital Devices, Regardless of Task Duration, Difficulty, or Viewing Distance

Abstract

Purpose: To compare blinking measured in situ during various tasks and examine relationships with ocular surface symptoms. The day-to-day repeatability of the blink rate and interblink interval was assessed.

Methods: Twenty-four students (28.6 ± 6.3 years; 8 male and 16 female) completed six reading tasks (printed text, laptop, TV, smartphone, smartphone at 50% brightness, smartphone with complex text), and two nonreading tasks (conversation, walking) in a randomized cross-over study. Ocular surface symptoms and clinical signs were assessed. The blink rate and interblink interval were measured using a wearable eye tracking headset. Blink parameters were compared across tasks and time (linear mixed model and post hoc comparisons with Bonferroni correction). Associations between blinking, symptoms, ocular surface, and clinical signs were assessed (Spearman's correlation). The smartphone reading task was completed twice to determine the coefficient of repeatability.

Results: The blink rate was lower (mean 10.7 ± 9.7 blinks/min) and the interblink interval longer (mean 9.6 ± 8.7 seconds) during all reading tasks compared with conversation (mean 32.4 ± 12.4 blinks/min; 1.5 ± 0.6 seconds) and walking (mean 31.3 ± 15.5 blinks/min; 1.9 ± 1.3s) (P < 0.001). There were no significant differences in blink parameters between any of the reading tasks or between conversation and walking. Changes in blinking occurred within 1 minute of starting the task. No associations were evident between blink rate or interblink interval and ocular surface symptoms or signs. The coefficient of repeatability was ±12.4 blinks/min for blink rate and ±18.8 seconds for interblink interval.

Conclusions: Spontaneous blinking can be measured reliably in situ. The blink rate was decreased and the interblink interval increased during reading compared with conversation and walking. Changes in blinking were immediate, sustained, and not associated with ocular surface symptoms or signs.

Figure 1.

Flowchart of study visits and order of clinical assessments. Note: Visit 2 was conducted 2 days after visit 1. Smartphone task was completed twice before other tasks at each visit for assessment of repeatability. Other tasks randomly allocated include six reading tasks (printed text, laptop, smart TV at 6 m, smartphone, smartphone at 50% brightness, smartphone more complex text), and two non -reading tasks (conversation, walking indoors). DEQ-5, Dry Eye Questionnaire 5; LLT, lipid layer thickness; NIBUT, noninvasive tear break-up time; OSDI, Ocular Surface Disease Index; TMH, tear meniscus height; SANDE, Symptoms Assessment in Dry Eye.

Figure 2.

Study set-up showing the wearable eye tracking headset (Pupil Labs GmbH) with two inbuilt high-speed adjustable eye cameras and a scene camera for real time monitoring from participants’ vantage point. The headset was worn by study participants during various tasks including reading from (a) printed text, (b) laptop, (c) smart TV at 6 m, (d) smartphone, and (e) walking indoors and conversation (not shown). The wearable eye tracking headset was connected to a laptop for task monitoring and data acquisition for all tasks other than walking indoors, where an android phone was used for the same purpose, while the examiner followed behind the participant holding the android phone to monitor recording (Fig. 2e). Participants’ consents were obtained for use of these images.

Figure 3.

(a) Blink rate and (b) interblink interval during various tasks of 15 minutes’ duration, measured using a wearable eye tracking headset (Pupil Labs GmbH) for 24 students with healthy eyes. Note that data from the first 3 minutes of the smartphone task were discarded and the remaining 12 minutes used for analysis. Data are presented as median and interquartile range. Open circles represent mild outliers (measurements >1.5 to 3.0 times the interquartile range) and stars represent extreme outliers (measurements >3 times the interquartile range).

Figure 4.

(a) Blink rate and (b) interblink interval during various tasks of 15 minutes duration, measured using a wearable eye tracking headset (Pupil Labs GmbH) for 24 students with healthy eyes. The tasks include six reading tasks (printed text, laptop, smart TV at 6 m, smartphone, smartphone at 50% brightness, smartphone more complex text), and two nonreading tasks (conversation, walking indoors). *Note, data from the first three minutes of the smartphone task were discarded and the remaining 12 minutes used for analysis.

Figure 5.

Ocular surface symptoms of discomfort and dryness scores (median and interquartile range) measured using the IOSS before and after various tasks of 15 minutes duration for 24 students with healthy eyes. Note, data from the first three minutes of the smartphone task were discarded and the remaining 12 minutes used for analysis. Higher IOSS scores indicate worse discomfort. Blue and red circles represent mild outliers (symptom scores >1.5 to 3.0 times the interquartile range).

Figure 6.

Differences between (a) blink rate and (b) interblink interval measured using the wearable eye tracking headset (Pupil Labs GmbH) during two repeats plotted against their mean for 24 students with healthy eyes, while reading easy book series on a smartphone for 12 minutes. The dotted line shows a bias of (a) −0.7 blinks/min (P = 0.62) and (b) 0.7s (P = 0.55). The dashed lines represent the limits of agreement of (a) +11.7 to −13.1 blinks/min and (b) +19.5 to −18.2s.