Dynamic assessment of the tear film muco-aqueous and lipid layers using a novel tear film imager (TFI).

PURPOSE: The objective of the study was to assess a new technology, the tear film imager (TFI), which can dynamically image the muco-aqueous and lipid layers. METHODS: Prospective pilot case series of individuals with and without dry eye (DE). Two sequential images were obtained with the TFI. Measurements were assessed for reproducibility and compared with clinically derived DE metrics. Individuals were grouped into DE categories based on signs of DE. RESULTS: 49 patients participated in the study with a mean age of 58.8 years (SD 15.9) and a female majority (69%). Reproducibility of the muco-aqueous layer thickness (MALT) was excellent (r=0.88). MALT measurements significantly correlated with the Schirmer score (r=0.31). Lipid break up time (LBUT) as measured by the TFI significantly correlated with the clinical measure of tear break up time (TBUT) (r=0.73). MALT and LBUT were significantly thinner and shorter, respectively, in the DE groups (mild-moderate and severe) compared with the control group. When comparing TFI parameters to clinically assessed signs, sensitivity of the device was 87% and specificity was 88%. CONCLUSION: The TFI is the first machine capable of reproducibly measuring muco-aqueous thickness in human subjects which correlates with Schirmer score. In parallel, it assesses other important aspects of tear film function which correlate with clinician assessed DE metrics.

Mapping the Lipid Layer of the Human Tear Film.

PURPOSE: To describe a new method to distinguish between normal versus lipid-deficient dry eye using a Tear Film Imager (TFI). METHODS: Two groups of study subjects, controls versus lipid-deficient dry eye, were tested using the TFI. This instrument provides an accurate measurement of the thickness and spatial distribution of the muco-aqueous and lipid layers of the tear film. The nanometer thickness resolution of the TFI enables the creation of detailed maps of the lipid layer thickness (LLT) across the corneal surface. These maps are captured with a large field of view of 6.5 mm diameter. RESULTS: A LLT map taken at 1 second from a blink end in the controls appears uniform, whereas a nonuniform layer was measured in the lipid-deficient dry eye. Lipid map uniformity can quantify the spatial variation of lipid across the cornea. A case study showed the ability to distinguish between controls [lipid map uniformity (LMU) = 14 nm] and lipid-deficient dry eye (LMU = 125 nm) through characterization of the LLT distribution. CONCLUSIONS: High-resolution lateral LLT maps demonstrate the significance of the lipid layer uniformity, which may play an important role in maintaining tear film health. LLT maps and the quantitative LMU could be used to diagnose and treat patients with dry eye.

Tear film imager for dynamic mapping of the human tear film.

Dry eye (DE) disease is a multifactorial disease of the outer ocular surface characterized by several ocular symptoms and mainly by tear film instability. We have developed an optical imaging system, the tear film imager (TFI), which is the first instrument that can directly image the muco-aqueous tear layer physical dimension in vivo and evaluate its parameters in a noninvasive mode with nanometer axial resolution. This instrument provides quantified information about many attributes of the tear film, including muco-aqueous layer thickness, lipid layer thickness, thickness change rate, and the break-up time. The TFI performances are based on simultaneous acquisition of large field of view (FOV) imagery and fast spectrometric measurement of the interference from the thin tear film sublayers. Herein, after describing the instrument and the methodology of the measurements, we use a tear film mock-up to quantify device accuracy (2.2 nm) and repeatability (0.25 nm standard deviation). In conclusion, we present a new technology for the assessment of the tear film with an unprecedented axial resolution and excellent accuracy and reproducibility.