Review of Literature on Measurements of Non-invasive Break Up Times, Lipid Morphology and Tear Meniscal Height Using Commercially Available Hand-held Instruments

Abstract

Purpose/aims: Dry eye is a common multi-factorial disease characterized by tearfilm dysfunction. Diagnosis of dry eye requires documentation of tear status with non-invasive tear break up times (NIBUT), tear meniscal height (TMH), and tearfilm lipid layer. These parameters objectively assess tear stability and indirectly, the functional impact of meibomian gland dysfunction. While it is obvious that portable instrumentation gives broader access than fixed instrumentation, its value would be limited if it is unreliable and its precision and accuracy substantially worse than fixed instruments.

Materials/methods: Because of the lack of systematic reviews concerning the Tearscope, we performed a scoping review of the literature to determine 1. the ranges of the tear parameters as measured by the device, 2. relationship between these measurements and other clinical variables, 3. Information about intra or inter-observer agreement, and comparison with another technique, where available.

Results: We found 22 reports related to NIBUT, 18 reports concerning tearfilm lipid morphology (LM) based on classification of interference patterns, and 8 reports on TMH. While publication of these reports indicates an acceptance of the reliability of portable instruments, we interrogated these studies further to evaluate the results obtained from portable devices and found that there was no equivalent measurements in fixed devices (LM) or measurements differ considerably from fixed devices (NIBUT). In the case of TMH, portable measurements were similar to those by traditional slit-lamp microscopy. There were relatively few studies on TMH measured using handheld devices, but it was found to be correlated to NIBUT but not the Schirmer test values.

Conclusions: Imaging algorithms in portable tearfilm instruments should be further standardized to facilitate wider adoption and evaluation. In the next few years, new emerging technologies will employ a strategy of non-invasive tear testing that is portable and relatively inexpensive, and these will enhance adoption of such tools in the clinic.

Keywords: Review; clinical study; diagnosis; dry eye; imaging; ocular disease; tear film; tear stability.