The effects of increasing ocular surface stimulation on blinking and sensation

Abstract

Purpose: The purpose of this study was to determine how increasing ocular surface stimulation affected blinking and sensation, while controlling task concentration.

Methods: Ten healthy subjects concentrated on a task while a custom pneumatic device generated air flow toward the central cornea. Six flow rates (FRs) were randomly presented three times each and subjects used visual analog scales to record their sensory responses. The interblink interval (IBI) and the FR were recorded simultaneously and the IBI, sensory response, and corresponding FR were determined for each trial. The FR associated with a statistically significant decrease in IBI, the blink increase threshold (BIT), was calculated for each subject.

Results: Both the mean and SD of IBI were decreased with increasing stimulation, from 5.69 ± 3.96 seconds at baseline to 1.02 ± 0.37 seconds at maximum stimulation. The average BIT was 129 ± 20 mL/min flow rate with an IBI of 2.33 ± 1.10 seconds (permutation test, P < 0.001). After log transformation, there was a significant linear function between increasing FR and decreasing IBI within each subject (Pearson's r ≤ -0.859, P < 0.05). The IBI was highly correlated with wateriness, discomfort, and cooling ratings (Pearson's r ≤ -0.606, P < 0.001).

Conclusions: There was a dose-response-like relationship between increased surface stimulation and blinking in healthy subjects, presumably for protection of the ocular surface. The blink response was highly correlated with ocular surface sensation, which is not surprising given their common origins. The BIT, a novel metric, may provide an additional end point for studies on dry eye or other conditions.

Keywords: blinking; ocular surface stimulation; sensation.

Figure 1

Blink response (Subject 1) to six levels of air stimulation from 0 (baseline) to 305 mL/min. Within each individual graph, the small vertical bars denote the timing of blinks and the horizontal line indicates the flow rate over the trial, with the average flow rate during the central 2 minutes shown at the top right corner. The BIT for this trial was 73 mL/min.

Figure 2

Individual example (Subject 1) using pooled data from three sets of trials. (A) IBI distributions under different flow rates. (B) Mean IBI as a function of flow rate. (C) Log transformation of IBI distributions under different flow rates. (D) Log transformation of mean IBI as a function of flow rate. A linear regression line was fitted to the data.

Figure 3

Blink response (Subject 2) to six levels of air stimulation from 0 (baseline) to 357 mL/min. Within each individual graph, the small vertical bars denote the timing of blinks and the horizontal line indicates the flow rate over the trial, with the average flow rate during the central 2 minutes shown at the top right corner. The BIT for this trial is 193 mL/min.

Figure 4

Individual example (Subject 2) using pooled data from three sets of trials. (A) IBI distributions under different flow rates. (B) Mean IBI as a function of flow rate. (C) Log transformation of IBI distributions under different flow rates. (D) Log transformation of mean IBI as a function of flow rate. A linear regression line was fitted to the data.

Figure 5

Blink response for all subjects. (A) IBI under different flow rates. (B) Log of IBI under different flow rates with linear regression line fitted for each subject.

Figure 6

Sensory response to different flow rates. Markers represent the average sensation from three trials with error bars. (A) Subject 1. (B) Subject 2.

Figure 7

Sensory response of all subjects (fitted with the Stevens' power function) to different flow rates. (A) Watery. (B) Discomfort. (C) Cooling. The arrow indicates a subject with low responses to the stimuli.

Figure 8

Correlation between IBI and the sensory response. A linear regression line was fitted for each sensation (Pearson's correlation coefficient, P < 0.001). (A) Watery. (B) Discomfort. (C) Cooling.