Estimation of scleral mechanical properties from air-puff optical coherence tomography.

We introduce a method to estimate the biomechanical properties of the porcine sclera in intact eye globes , using optical coherence tomography that is coupled with an air-puff excitation source, and inverse optimization techniques based on finite element modeling. Air-puff induced tissue deformation was determined at seven different locations on the ocular globe, and the maximum apex deformation, the deformation velocity, and the arc-length during deformation were quantified. In the sclera, the experimental maximum deformation amplitude and the corresponding arc length were dependent on the location of air-puff excitation.

Multi-meridian corneal imaging of air-puff induced deformation for improved detection of biomechanical abnormalities.

Corneal biomechanics play a fundamental role in the genesis and progression of corneal pathologies, such as keratoconus; in corneal remodeling after corneal surgery; and in affecting the measurement accuracy of glaucoma biomarkers, such as the intraocular pressure (IOP). Air-puff induced corneal deformation imaging reveals information highlighting normal and pathological corneal response to a non-contact mechanical excitation. However, current commercial systems are limited to monitoring corneal deformation only on one corneal meridian.

Corneal Collagen Ordering After In Vivo Rose Bengal and Riboflavin Cross-Linking.

Purpose: Photoactivated cornea collagen cross-linking (CXL) increases corneal stiffness by initiating formation of covalent bonds between stromal proteins. Because CXL depends on diffusion to distribute the photoinitiator, a gradient of CXL efficiency with depth is expected that may affect the degree of stromal collagen organization. We used second harmonic generation (SHG) microscopy to investigate the differences in stromal collagen organization in rabbit eyes after corneal CXL in vivo as a function of depth and time after surgery.

Quantization of collagen organization in the stroma with a new order coefficient.

Many optical and biomechanical properties of the cornea, specifically the transparency of the stroma and its stiffness, can be traced to the degree of order and direction of the constituent collagen fibers. To measure the degree of order inside the cornea, a new metric, the order coefficient, was introduced to quantify the organization of the collagen fibers from images of the stroma produced with a custom-developed second harmonic generation microscope. The order coefficient method gave a quantitative assessment of the differences in stromal collagen arrangement across the cornea depths and between untreated stroma and cross-linked stroma.

Three-dimensional tracking of a single fluorescent nanoparticle using four-focus excitation in a confocal microscope.

We report high sensitivity detection and tracking of a single fluorescent nanoparticle in solution by use of four alternately pulsed laser diodes for fluorescence excitation in a confocal microscope. Slight offsets between the centers of the overlapping laser foci together with time-resolved photon counting enable sub-micron precision position measurements. Real-time correction for diffusional motion with a xyz-piezo stage then enables tracking of a nanoparticle with diffusivity up to ~12 μm(2) s(-1).