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V. Aranha dos Santos, L. Schmetterer, M. Gröschl, G. Garhofer, R.M. Werkmeister:
"In vivo tear film thickness measurement and tear film dynamics visualization using spectral domain OCT and an efficient delay estimator";
Vortrag: SPIE 9697, Optical Coherence Tomography and Coherence Domain Optical Methods, San Francisco, CA, USA; 15.02.2016; in: "Proc. SPIE 9697, Optical Coherence Tomography and Coherence Domain Optical Methods", (2016), S. 96970601 - 96970611.

Dry eye syndrome is a highly prevalent disease of the ocular surface characterized by an instability of the tear
lm. Traditional methods used for the evaluation of tear lm stability are invasive or show limited repeatability.
Here we propose a new noninvasive approach to measure tear lm thickness using an e cient delay estimator
and ultrahigh resolution spectral domain OCT. Silicon wafer phantoms with layers of known thickness and
group index were used to validate the estimator-based thickness measurement. A theoretical analysis of the
fundamental limit of the precision of the estimator is presented and the analytical expression of the Cram er-
Rao lower bound (CRLB), which is the minimum variance that may be achieved by any unbiased estimator, is
derived. The performance of the estimator against noise was investigated using simulations. We found that the
proposed estimator reaches the CRLB associated with the OCT amplitude signal. The technique was applied in
vivo in healthy subjects and dry eye patients. Series of tear lm thickness maps were generated, allowing for the
visualization of tear lm dynamics. Our results show that the central tear lm thickness precisely measured in
vivo with a coe cient of variation of about 0.65% and that repeatable tear lm dynamics can be observed. The
presented method has the potential of being an alternative to breakup time measurements (BUT) and could be
used in clinical setting to study patients with dry eye disease and monitor their treatments.

Tear lm, dry eye, delay estimator, Cram er-Rao lower bound