Techniques for In Vivo Assessment of Corneal Biomechanics: Brillouin Spectroscopy and Hydration State - Quo Vadis?

To assess the structural integrity of the cornea, non-invasive methods are needed for the local measurement of its mechanical properties. Among a number of established techniques and their associated advantages and disadvantages, Brillouin spectroscopy is still a relatively new technique, capable of determining the compressive modulus of biological tissue, specifically the cornea, in vivo. In the present paper, these various existing and developing technologies for corneal biomechanics are discussed and correlated.

[Imaging Properties of Spectacle Lenses and their Influence on the Tolerance of Spectacle Correction].

It is not uncommon for patients to complain about incompatibility with the glasses made, although an eyeglass determination has been performed with utmost precision. The causes for this can vary. Thus, the specification of the corneal vertex distance (HSA) is mandatory when prescribing spectacles in order to ensure the exact conversion of the measured values into the values in use.

[Effect of the Age-Related Corneal Elasticity on Applanation Tonometry].

Elevated intraocular pressure (IOP) is accepted to be one important criterion for glaucoma and is usually measured by applanation or rebound tonometry. The individual uncertainty due to central cornea thickness (CCT) is thereby corrected, while the error induced by age-related elastic modulus (EM) change of the cornea is ignored. To investigate its influence on IOP measurement, we derive a model including also the elastic modulus.

Visualization of IOL Material-Induced Changes in Retinal Color Stimulus.

Purpose. Different IOL materials, particularly blue-light filtering materials, have different spectral transmittance characteristics. The color stimuli, which influence retinal receptors objectively, have consequently implications for color perception.

Spectral behavior of second harmonic signals from organic and non-organic materials in multiphoton microscopy.

Multimodal nonlinear microscopy allows imaging of highly ordered biological tissue due to spectral separation of nonlinear signals. This requires certain knowledge about the spectral distribution of the different nonlinear signals. In contrast to several publications we demonstrate a factor of [Formula: see text] relating the full width at half maximum of a gaussian laser pulse spectrum to the corresponding second harmonic pulse spectrum in the spatial domain by using a simple theoretical model.

Ex vivo measurement of postmortem tissue changes in the crystalline lens by Brillouin spectroscopy and confocal reflectance microscopy.

Use of Brillouin spectroscopy in ophthalmology enables noninvasive, spatially resolved determination of the rheological properties of crystalline lens tissue. Furthermore, the Brillouin shift correlates with the protein concentration inside the lens. In vitro measurements on extracted porcine lenses demonstrate that results obtained with Brillouin spectroscopy depend strongly on time after death.

Spatially resolved Brillouin spectroscopy to determine the rheological properties of the eye lens.

Presbyopia is closely associated with the loss of accommodation, and hence with a decline in the viscoelastic properties of the human eye lens. In this article we describe a method for obtaining spatially resolved in vivo measurements of the rheological properties of the eye lens, based on the spectroscopic analysis of spontaneous Brillouin scattering using a virtually imaged phased array (VIPA). The multi-pass configuration enhances resolution to the extent that measurements are possible in elastic biological tissue characterized by intense scattering.