Ocular Protection Index

The Ocular Protection Index (OPI) demonstrates how the TFBUT and inter-blink interval (IBI) interact to protect the corneal surface.¹ If the amount of time between blinks is longer than TFBUT, an insufficient tear film leaves the corneal epithelial cells unprotected, exacerbating the signs and symptoms of dry eye.

When the ocular surface is sufficiently protected by tears (or when TFBUT exceeds the inter-blink interval), the signs and symptoms of dry eye may be minimized.

The Non-Invasive Tear Film Break-up Time Test

There is no single test to diagnose dry eye. However, a simple indicator is the Non-Invasive Tear Break-up Time (NIBUT) test. NIBUT is determined with the following steps:

1. Obtain a stop watch or clock;
2. Have the patient blink 2 times then stare straight ahead;
3. Ask the patient to avoid blinking as long as possible AND to indicate when ocular discomfort begins (itchiness, foreign body sensation, etc.);
4. Record the amount of time (in seconds) that transpires between the last complete blink and the moment they experience ocular discomfort;
5. This time is the NIBUT.

NIBUT² is considered a valid measurement of tear break-up, as research has shown nearly 4 out of 5 patients experience ocular awareness followed by discomfort within 1 second of TFBUT.¹

1. Ousler GW, Emory TB, Welch D, Abelson MB. Factors that influence the inter-blink interval (IBI) as measured by the ocular protection index (OPI). (Poster presentation) The Association of Research in Vision and Ophthalmology (ARVO), 2002.

2. Nally L, Ousler GW, Abelson MB. Ocular discomfort and tear film break-up time in dry eye patients: a correlation. IOVS 2000 41;4 (ARVO Abstract):1436.