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P.J. Murphy, A.M. Ntola, C. Purslow, J.S. Wolffsohn, E.I. Pearce; An Investigation Of The Ocular Surface Sensory Trigger For Blinking . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1948.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the hypothesis that localised cooling in the tear film, produced by tear thinning prior to break–up, allows increased evaporation, which is detected by the corneal nerves, initiating a blink.
Twenty Caucasian subjects (9 males, 11 females, mean ± sd age: 22.85 ± 2.2 years) were recruited. Subjects attended on two days, after 12pm to avoid any diurnal variation, and the following measurements were made at selected time points. At the first visit: blink frequency, as defined by the inter–blink interval (IBI), corneal sensitivity (CS), fluorescein (0.7µl, 2%) tear film break–up time (FBUT), post–blink cooling by ocular surface thermography (OST) and tear film evaporation rate (TER) were measured. At the second visit: 20µl of 0.5% proxymetacaine hydrochloride was instilled, and CS, OST and TER measured after 2 and 20 minutes.
A strong correlation was found between IBI and FBUT (Spearman's, r=0.926, p<0.0001). No correlation was found between IBI and CS for subjects with good sensitivity (Spearman's, r=0.236, p=0.315), although less sensitive subjects were found to blink more often (Mann–Whitney, p=0.009). No correlation was found between IBI and TER (Spearman's, r=–0.32, p=0.1), or IBI and OST (Spearman's; rate of change: r=–0.038, p=0.874, total temperature change: r=–0.017, p=0.945). Corneal anaesthesia produced longer IBI (Wilcoxon, p<0.0001) and increased TER (Kruskal–Wallis, p=0.029), but no change in OST (Kruskal–Wallis; rate of change: p=0.169, total temperature change, p=0.224). Fluorescein caused an increase in TER (Wilcoxon, p=0.037), but no change in OST (Wilcoxon; rate of change: p=0.716, total temperature change, p=0.133).
1) Tear film break–up is a trigger for blinking, as shown by the IBI decreasing with a reduction in tear stability. 2) The corneal nerves detect thinning of the tear film prior to break–up and initiate a blink – subjects with low CS blink less frequently, suggesting that early changes in tear film are not detected. 3) Post–blink changes in TER and OST did not appear to influence IBI suggesting either that evaporative cooling is not a factor in the blink mechanism, or that limitations in current instrument design mean more subtle changes are not detected.
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