High-resolution thermography shows real-time dynamic tear film formation

Purpose: The purpose of this study was to compare the thermographic tear film spread dynamics with the tear film lipid layer dynamics observed with interferometry. This was done to test the hypothesis that the spread of the lipid layer of the tear film can be seen with high-resolution infrared imaging. Methods: Tear film dynamics of healthy participants (n = 14; 29 ± 12 years) were recorded using a high-resolution infrared camera (TearView) and video-interferometer (DR1-alpha). The dynamics of a “dark band”, a feature observed post-blink in the infrared images and resembling lipid layer spread, were compared to lipid layer front and particle movement seen in interferometry using tracking software. Results: Infrared imaging revealed a dark band moving rapidly upward post-blink, disappearing at the superior lid margin, followed by a stable, uniform tear film. This dynamic mirrored lipid layer spread observed via interferometry but was significantly faster. The mean velocity at 200 ms after t₀ of 9.6 ± 2.3 mm/s for the dark band compared to 5.8 ± 1.8 mm/s and 5.3 ± 1.7 mm/s for lipid layer front and lipid particles, respectively (p < 0.001). Conclusion: High-resolution thermography is likely not detecting features of the lipid layer observable with interferometry but instead visualizes the leading edge of a newly forming tear film after a blink. This offers a non-invasive, real-time method to evaluate tear film dynamics under natural conditions and could have diagnostic utility. High-resolution thermography adds to the toolkit of traditional surrogate techniques used for evaluating the tear film (e.g., instillation of fluorescein, projection of Placido rings onto the eye).