We are introducing a proof-of concept method to estimate scleral mechanical properties from air-puff deformation imaging using optical coherence tomography (OCT), customized surface segmentation methods, and 3D finite element analysis on porcine eyes.
Air-puff induced corneal deformation imaging reveals information highlighting normal and pathological corneal response to a non-contact mechanical excitation. Here, we present a novel customized swept-source optical coherence tomography system coupled with a collinear air-puff excitation. We acquired unobstructed dynamic corneal deformation on multiple meridians with two custom scan patterns over a field of view of up to 15 mm x 15 mm and selected puff profiles at unprecedented scan rates, both ex vivo and in vivo. We show that our system can detect corneal deformation profiles and deformation asymmetries that are useful for corneal biomechanics diagnostics and pathology screening.
We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a confocal one- or twophoton
microscope with four-focus pulse-interleaved excitation and time-gated single-photon counting. As the technique
is scalable to multiple detectors for multi-color observations, it can be used to find the separations of differently colored
molecules over a distance range that is complementary to that achievable by FRET. Also, there is a possibility for
improved spatial localization by using the nonlinearity of saturation of the excitation or by using the technique together
with imaging of the point spread function. Applications of two experimental set-ups for four-focus fluorescence
excitation for studies of quantum dots and single-particle manipulation and trapping are also discussed.
A freely diffusing single fluorescent molecule may be scrutinized for an extended duration within a confocal microscope
by actively trapping it within the femtoliter probe region. We present results from computational models and ongoing
experiments that research the use of multi-focal pulse-interleaved excitation with time-gated single photon counting and
maximum-likelihood estimation of the position for active control of the electrophoretic and/or electro-osmotic motion
that re-centers the molecule and compensates for diffusion. The molecule is held within a region with approximately
constant irradiance until it photobleaches and/or is replaced by the next molecule. The same photons used for
determining the position within the trap are also available for performing spectroscopic measurements, for applications
such as the study of conformational changes of single proteins. Generalization of the trap to multi-wavelength excitation
and to spectrally-resolved emission is being developed. Also, the effectiveness of the maximum-likelihood position
estimates and semi-empirical algorithms for trap control is discussed.
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