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V. Aranha dos Santos, L. Schmetterer, G. Triggs, R. Leitgeb, M. Gröschl, A. Messner, D. Schmidl, G. Garhofer, G. Aschinger, R.M. Werkmeister:
"Super-resolved thickness maps of thin film phantoms and in vivo visualization of tear film lipid layer using OCT";
Biomedical Optics Express, 7 (2016), 7; 2650 - 2670.

In optical coherence tomography (OCT), the axial resolution
is directly linked to the coherence length of the employed light source.
It is currently unclear if OCT allows measuring thicknesses below its
axial resolution value. To investigate spectral-domain OCT imaging in the
super-resolution regime, we derived a signal model and compared it with
the experiment. Several island thin film samples of known refractive indices
and thicknesses in the range 46􀀀163 nm were fabricated and imaged. Reference
thickness measurements were performed using a commercial atomic
force microscope. In vivo measurements of the tear film were performed
in 4 healthy subjects. Our results show that quantitative super-resolved
thickness measurement can be performed using OCT. In addition, we
report repeatable tear film lipid layer visualization. Our results provide a
novel interpretation of the OCT axial resolution limit and open a perspective
to deeper extraction of the information hidden in the coherence volume.