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M. Schindelar, G.W. Ousler, III, M.B. Abelson; Effect of Tear Film Stability on Ocular Surface Damage in a Population of Dry Eye Patients . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4457.
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The Ocular Protection Index (OPI) demonstrates how the interaction between tear film break–up time (TFBUT) and the inter–blink interval (IBI) help regulate the integrity of an ocular surface. A protected surface exists when the TFBUT matches or exceeds the IBI. In contrast, an unprotected surface exists when TFBUT is less than the IBI. This is clinically relevant since repeated intermittent exposure of a tear film deficient cornea can lead to ocular discomfort and the development of clinical signs such as keratitis and redness. Studies have shown that patients experience ocular symptoms within a second of TFBUT. The purpose of this study was to examine the effect of decreased TFBUT on corneal and conjunctival staining in a population of dry eye patients. Two–hundred and thirty–seven (237) patients diagnosed with dry eye underwent ophthalmic evaluations including visual acuity, TFBUT (using a digital imaging system with an on–screen timer), and fluorescein / lissamine green staining (standardized 0 to 4 point scale per region). Patients were then categorized into two groups according to tear film stability: 1) unprotected: TFBUT less than 4 sec and 2) protected: TFBUT ≥ 4 sec. The mean TFBUT in the unprotected patients (n = 202) was 2.32 ± 0.69 while the mean TFBUT in the protected patients (n = 35) was 6.24 ± 2.18. The following table shows that corneal and conjunctival staining was significantly higher in patients with a decreased TFBUT or a less protected ocular surface.
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