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GW Ousler, TB Emory, D Welch, MB Abelson; Factors that Influence the Inter-Blink Interval (IBI) as Measured by the Ocular Protection Index (OPI) . Invest. Ophthalmol. Vis. Sci. 2002;43(13):56.
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Purpose: To better understand the factors which influence the inter-blink interval (IBI) and identify an improved definition for clinically relevant alterations in tear film break-up time (TFBUT). Methods: Eight (8) subjects underwent baseline examinations including visual acuity, ocular discomfort (0-4 scale) and blink rate. A digital, micro-camera equipped with an infrared illuminator was used to monitor blink rate by tracking the diameter of a subject's pupil. This device was mounted to a headset extension and directed towards the eye so that a complete blink (defined as ≷95% decrease in pupil diameter) could be measured non-invasively. Subjects were then placed in a controlled adverse environment (CAE) which regulates humidity (<5% RH), temperature (76° F), airflow (constant, non-turbulent) and visual tasking (video display terminal) for 90 minutes. During the CAE exposure, blink rate was measured every 10 minutes while ocular discomfort was recorded every 5 minutes. After the CAE exposure, baseline procedures were repeated. Results: Mean blink rate increased significantly from 11 blinks/minute pre-CAE to 20 blinks/minute post-CAE (a 9 blinks/minute increase, p = 0.039). Mean ocular discomfort also increased significantly from 0.63 unit pre-CAE to 2.38 units post-CAE (a 1.75 units increase, p = 0.003). Conclusion: This data demonstrates that both blink rate and ocular discomfort increase significantly when exposed to a CAE for 90 minutes. When examining the relationship between TFBUT and the IBI, it may be suggested that their interactions help regulate the integrity of an ocular surface. For example, a protected ocular surface exists when TFBUT either matches or exceeds the IBI. In contrast, an unprotected ocular surface exists when TFBUT is less than the IBI. This interaction can be clinically relevant since repeated, intermittent exposures of a tear film deficient cornea leads to ocular discomfort followed by keratitis. Consequently, an Ocular Protection Index (OPI) that quantifies the relationship between TFBUT and the IBI has been developed and proven to be useful in assessing factors that cause dry eye and evaluating its therapeutic agents.
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