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Scott Liddle, Steve M. Grenon, Caroline A. Blackie, Donald R. Korb; A Novel Approach For Simulating The Precorneal Tear Film For Interferometric Measurement. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4248.
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© ARVO (1962-2015); The Authors (2016-present)
To design, fabricate, and test phantoms that mimic the precorneal tear film. In particular, the phantoms optically simulate the aqueous layer of the tear film and the lipid layer at specific thicknesses for purposes of interferometric measurement of lipid layer thickness.
Optical phantoms were developed using crown glass and a thin film vapor-deposited magnesium oxide (MgO) coating, which produce interference colors that closely mimic those produced by the lipid and aqueous layers in the precorneal tear film. The optical properties of the lipid and aqueous layers were obtained from the literature. Phantoms were created with nine unique MgO thicknesses to simulate various lipid layer thicknesses. The thickness of the MgO layer of each phantom was corroborated by third-party ellipsometry measurement. A digital recording of each unique phantom was captured using the LipiView Ocular Surface Interferometer. The interferometric data were extracted from each digital recording to determine the relationship between interference color and the MgO thickness of the phantom, which was used to calibrate the LipiView system. The thicknesses of a second set of optical phantoms were then measured using the calibrated LipiView, and compared to the ellipsometry data for the second set of phantoms.
The ellipsometry measurements confirmed that the thickness of the MgO layer and its index of refraction were similar to the desired values. Digital recordings were captured for each of the nine phantoms on three LipiView systems and the LipiView software was used to generate a thickness measurement. The lipid layer thicknesses mimicked by the phantoms ranged from 20 to 283 nm. The average difference in thicknesses reported by the LipiView to the ellipsometry-measured thicknesses was 3.8 nm. The maximum error observed for a single measurement was 9 nm.
The ellipsometry data show that the phantoms had the desired optical properties, and, therefore, the interference colors produced are similar to those produced by the tear film, as described in the literature. The phantom thickness measurements recorded by the LipiView closely match the ellipsometry measurements, demonstrating the ability of the LipiView to measure absolute thickness through interferometry within the range of 20 to 283 nm.
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