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.

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.

Hyperspectral imaging camera using wavefront division interference.

An approach for performing hyperspectral imaging is introduced. The hyperspectral imaging is based on Fourier transform spectroscopy, where the interference is performed by wavefront division interference rather than amplitude division interference. A variable phase delay between two parts of the wavefront emanating from each point of an object is created by a spatial light modulator (SLM) to obtain variable interference patterns. The SLM is placed in the exit pupil of an imaging system, thus enabling conversion of a general imaging optical system into an imaging hyperspectral optical system. The physical basis of the new approach is introduced, and an optical apparatus is built.

Spatial-phase-shift imaging interferometry using a spectrally modulated white light source.

An extension of the white light spatial-phase-shift (WLSPS) for object surface measurements is described. Using WLSPS, surface measurements can be obtained from any real object image without the need of a reference beam, thus achieving inherent vibration cancellation. The surface topography is obtained by acquiring multiple images of an object illuminated by a spectrally modulated white light source and using an appropriate algorithm. The modulation of the light source obviates the need for the continuous phase delay to obtain the interferograms.

Surface measurements by white light spatial-phase-shift imaging interferometry.

A novel method of common-path imaging interferometry, the White Light Spatial-Phase-Shift (WLSPS) for object surface measurements, is discussed here. Compared to standard White Light Interferometry (WLI), which uses a reference mirror, the interferometry of WLSPS is obtained by creating manipulations to the light wavefront reflected from an object's surface. Using this approach, surface measurements can be obtained from any real object image, and do not need to be taken directly from the object itself. This creates the ability for a surface measurement tool to be attached to any optical system that generates a real image of an object. Further, as this method does not require a reference beam, the surface measurement system contains inherent vibration cancelation.