Because the tear film’s lipid layer serves as a barrier to prevent the aqueous component from evaporating, it is arguably the most important component of tears. But relatively little is known about how it forms, breaks down and disperses. These characteristics are likely to be deeply intertwined with the dynamics of the overall tear film, but direct observation of these effects have been limited by technological hurdles that prevent simultaneous analysis of both the entire tear film and a single component such as the lipid layer.
Knowing that the ability to simultaneously image the lipid layer thickness and the total tear film thickness would increase understanding of how the lipid layer assembles and interacts with other tear components, a team of researchers from the University of Alabama at Birmingham developed an imaging system that integrates optical coherence tomography (OCT) and thickness-dependent fringe interferometry imaging into one device.
The OCT used in the study had an axial resolution of 1.38µm, providing an accurate measurement of the overall tear film thickness. The interferometer can detect a change as small as 15nm in lipid layer thickness, and its spatial resolution in the x–y plane is 5µm.
The researchers used both technologies to examine the effect of instilling artificial tears. For both contact lens and non-contact lens wearers, thickness of the pre-corneal tear film immediately increased (from 4.4 ±0.97µm to 20.3 ±3.6µm), but then gradually decreased to 8.8 ±2.1µm at four minutes post-instillation.
Lipid layer thickness was simultaneously quantified using the interferometry element of the device. The thicknesses of the lipid layer were 62.4 ±14.5nm at pre-instillation, 48.7 ±5.3nm at post-instillation and 55.2 ±9.8nm at four minutes later.
Though this particular study did not reveal findings of note for clinical practice, it serves as a stepping-stone toward future studies that will allow lipid/aqueous interactions to be studied in more detail. This proof-of-concept study showed that multiple imaging technologies can be combined to capture tear film data heretofore unavailable to researchers.