Abstract
To extend our understanding of tear film dynamics for the management of dry eye disease, we propose a method to optically sense the tear film and estimate simultaneously the thicknesses of the lipid and aqueous layers. The proposed method, SDT-OCT, combines ultra-high axial resolution optical coherence tomography (OCT) and a robust estimator based on statistical decision theory (SDT) to achieve thickness measurements at the nanometer scale. Unlike conventional Fourier-domain OCT where peak detection of layers occurs in Fourier space, in SDT-OCT thickness is estimated using statistical decision theory directly on the raw spectra acquired with the OCT system. In this paper, we demonstrate in simulation that a customized OCT system tailored to ~1 µm axial point spread function (FWHM) in the corneal tissue, combined with the maximum-likelihood estimator, can estimate thicknesses of the nanometer-scale lipid and micron-scale aqueous layers of the tear film, simultaneously, with nanometer precision. This capability was validated in experiments using a physical phantom that consists of two layers of optical coatings that mimic the lipid and aqueous layers of the tear film.
Highlights
Dry Eye Disease (DED) has been a serious public health issue, with symptoms including discomfort, visual disturbance, and irritation that may cause damage to the ocular surface [1]
The lipid layer is secreted by the meibomian gland and is about 20~150 nm thick; underneath the lipid lies the aqueous layer, which contributes the largest volume to the tear and is about 3~7 μm thick; the mucin layer is the interface between the aqueous layer and the cornea, which creates a rough interface between the cornea and the aqueous layer
Results show a good agreement in the evaluation of the point spread function (PSF) and the achievement of < 1μm axial PSF needed for this application
Summary
Dry Eye Disease (DED) has been a serious public health issue, with symptoms including discomfort, visual disturbance, and irritation that may cause damage to the ocular surface [1]. The tear film is the ocular surface fluid that contributes to keep the cornea healthy and functional, and as such it plays a critically important role in keeping normal visual function for the ocular optical system [3]. The normal tear film consists of three layers: the lipid layer, the aqueous layer, and the mucin layer [4]. The lipid layer is secreted by the meibomian gland and is about 20~150 nm thick; underneath the lipid lies the aqueous layer, which contributes the largest volume to the tear and is about 3~7 μm thick; the mucin layer is the interface between the aqueous layer and the cornea, which creates a rough interface between the cornea and the aqueous layer. The rough interface serves to attach tears to the corneal surface
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