Karsten Sperlich

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. The intensity of the Brillouin signal decreases significantly as early as 5 h postmortem. Moreover, the fluctuation of the Brillouin frequency shift inside the lens increases with postmortem time. Images of lens tissue taken with a confocal reflectance microscope between measurements reveal a degenerative aging process. These tissue changes correlate with our results from Brillouin spectroscopy. It is concluded that only in vivo measurements appropriately reflect the rheological properties of the eye lens and its protein concentration.

Quantum efficiency measurements of (EM)CCD cameras: high spectral resolution and temperature dependence

Nowadays, CCD cameras can be found in every optical laboratory for highly diverse purposes. Measuring quantitatively spectral-dependent intensities implies that the spectral quantum efficiency (SQE) has to be taken into account, at least if the width of the spectrum is more than a few nm. The determination of the SQE is usually considered to be a tedious challenge with rather inaccurate results. However, we show in this paper that with calibrated photo diodes, this has become an affordable and straightforward task. In this paper, we examined the SQE of one front- and five back-illuminated electron multiplying CCD cameras from Andor Technology in the range of 350–1080 nm with a spectral resolution of up to 1 nm. The temperature dependence of the SQE has been investigated in the spectral interval given above between +20 and −80 °C. We observed unexpected oscillations in the SQE for the front-illuminated camera. For back-illuminated cameras with an ultraviolet conversion layer, the measured SQE turns out to be very different from the manufacturer data, which results from the transmittance spectrum of the conversion layer. For conventional back-illuminated cameras without a conversion layer, we observed interesting crossing behavior in the temperature-dependent measurements.

Unambiguous ultrashort pulse reconstruction from double spectrograms alone

We report a spectrographic technique for amplitude and phase measurements of ultrashort laser pulses (above 10 fs). Pulse information is obtained directly from two different spectrograms, using the mathematical relations between Wigner–Ville function projections. Pulses are reconstructed rapidly and unambiguously without stagnation. This non-interferometric method is demonstrated experimentally for the successful characterization of 100 fs pulses.

3D confocal laser-scanning microscopy for large-area imaging of the corneal subbasal nerve plexus

The capability of corneal confocal microscopy (CCM) to acquire high-resolution in vivo images of the densely innervated human cornea has gained considerable interest in using this non-invasive technique as an objective diagnostic tool for staging peripheral neuropathies. Morphological alterations of the corneal subbasal nerve plexus (SNP) assessed by CCM have been shown to correlate well with the progression of neuropathic diseases and even predict future-incident neuropathy. Since the field of view of single CCM images is insufficient for reliable characterisation of nerve morphology, several image mosaicking techniques have been developed to facilitate the assessment of the SNP in large-area visualisations. Due to the limited depth of field of confocal microscopy, these approaches are highly sensitive to small deviations of the focus plane from the SNP layer. Our contribution proposes a new automated solution, combining guided eye movements for rapid expansion of the acquired SNP area and axial focus plane oscillations to guarantee complete imaging of the SNP. We present results of a feasibility study using the proposed setup to evaluate different oscillation settings. By comparing different image selection approaches, we show that automatic tissue classification algorithms are essential to create high-quality mosaic images from the acquired 3D datasets.

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. We report on the quantitative determination of IOL-specific transmittance characteristics and present a method visualizing the resultant changes in color stimulus. Methods. A setup was realized to quantify IOL-absorption in a range of 390–780 nm. To visualize the influence of the different spectral transmittance characteristics an algorithm was developed, which converts RGB-pixel values of images into spectra, which performs the corresponding transmittance correction, reconverts to RGB, and reconstructs the image. IOLs of hydrophobic acrylate and hydrophilic acrylate with a hydrophobic surface in each case with/without blue-light filter were examined. Results. Assessment of the reference images verifies the suitability of the pipeline. Evaluation of the transmittance spectra reveals differences of material- and manufacturer-specifics, which are capable of inducing considerable changes in color perception, particularly in the blue color range and mixed colors involving blue. Conclusions. The developed technique provides an approach for determining IOL-specific transmittance behavior and subsequently its influence on the retinal color stimulus. Problems of altered color perception are occasionally reported after cataract surgery and these become obvious with the visualization procedure developed here.

Phase and intensity retrieval of ultrashort laser pulses with single-shot VAMPIRE

We present a single-shot (SH) self-referencing technique for measuring phase and intensity of ultrashort laser pulses (SH-VAMPIRE). The cross-correlation setup utilizes filter elements to circumvent relative-phase or direction of time ambiguities.