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J. Rodriguez, E. Angjeli, K. J. Lane, R. White, S. Breton, M. B. Abelson; Correlation Between Blink Rate, Tear Film Corneal Protection, and Corneal Staining. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3389.
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Increased blink rate may be an indication of ocular irritation and can function as a compensatory action in dry eye. Prolonged under-hydration of the corneal surface results in cellular shrinkage, observable by fluorescein staining, and can eventually lead to epithelial cell damage. However, the relationship between an increase in blink rate, the extent of corneal staining and the severity of tear film instability, assessed as corneal area protected by tear film within a undisturbed blink pattern, has not been clearly demonstrated.
Sixteen dry eye subjects were included in a one visit study based on staining symptoms, and a blink rate > 6 blinks/min. One minute video clips of blink patterns in the presence of staining were recorded then analyzed manually for presence of tear film break up. For grading purposes, the cornea was subdivided into 17 regions, with each region graded in a binary manner as either having an intact or disrupted tear film. An algorithm was developed for incorporating both a time and area component as an Ocular Protection Index (enhanced OPI). Total corneal staining was assessed using a 0-4 scale. The subject were divided into two groups for analysis; one with inter-blink interval (IBI)<5sec and IBI>5 sec.
Subjects with a mean IBI<5 seconds had higher staining scores (sum=5.25, ±1.56) than subjects with a mean IBI>5 seconds (sum=3.96, ±1.49) (p=0.055). Individuals with a mean IBI<5 seconds also exhibited significantly greater corneal protection over the one minute video (area protected=93.4%, ±4.7%) than those with a mean IBI>5 seconds (area protected=88.5%, ±11.2%) (p=0.041).
This study demonstrates that those subjects with higher staining scores, are actively compensating with a shorter IBI and consequently have greater corneal coverage. Subjects with less staining have a less compensatory blink rate, and thus have lesser amounts of corneal protection. This suggests that low corneal protection precedes a severe dry stage, and lower IBI is a compensatory mechanism. In a drug development process, identification and control of these compensatory mechanisms becomes crucial for standardization.
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