Michael Pircher

Polarization-sensitive optical coherence tomography in the anterior mouse eye (Conference Presentation)

Polarization-sensitive optical coherence tomography (PS-OCT) provides intrinsic contrast related to tissue microstructure. In the past, PS-OCT has been successfully used for imaging the anterior eye of humans in a variety of pathologic conditions. Here, we present PS-OCT imaging of the anterior eye in mice. Spectral domain PS-OCT centered at a wavelength of 840 nm was performed in anaesthetized laboratory mice. Three dimensional data sets were acquired at a 70 kHz A-line rate. PS-OCT images displaying phase retardation, birefringent axis orientation and degree of polarization uniformity (DOPU) were computed. Similar to human anterior segments, depolarization was observed in the corneal stroma and in structures containing melanin pigments such as the iris and the ciliary body. Birefringence was detected in the sclera close to the limbus. Aside from depolarizing foci observed within structures affected by cataract, the lens appeared mostly polarization preserving. Increased birefringence was observed in a scarred cornea. Given the similarity of the polarization characteristics in the murine eye and the human eye, PS-OCT lends itself as an ideal candidate for non-invasive imaging in preclinical studies in mouse models of anterior segment pathology.

Large field of view adaptive optics scanning laser ophthalmoscopy and optical coherence tomography (Conference Presentation)

Adaptive Optics (AO) retinal imaging is revealing microscopic structures of the eye in a non-invasive way. Due to anisoplanatism, conventional AO systems are efficient on small 1°x1° field of view (FoV). We present a lens-based AO scanning laser ophthalmoscope (SLO) set-up with 2 deformable mirrors (DM), providing high-resolution retinal imaging on a 4°x4° FoV, for an eye pupil diameter of 7 mm. The first DM is in a pupil plane and is driven using a Shack-Hartmann (SH). The second DM is conjugated to a plane located 0.7 mm in front of the retina, to correct for aberrations varying within the FoV. Its shape is optimized using sensorless AO technique. nThe performance of this set-up was characterized in-vivo by measuring the eyes of four healthy volunteers. The obtained image quality was satisfactory and uniform over the entire FoV. Foveal cones could be resolved and no image distortion was detected. Furthermore, a 10°x10° FoV image was acquired at the fovea of one volunteer, by stitching 9 images recorded at different eccentricities. Finally, different layers of the retina were imaged. In addition to the photoreceptors mosaic, small capillaries and nerve fibers were clearly identified.nThe presented AO-SLO instrument provides high-resolution images of the retina on a relatively large FoV in reasonable time. With 2 DMs, one SH and no guide star, the system stays quite simple. The imaging performance of the set-up was validated on 4 healthy volunteers and we are currently imaging patients with different eye diseases.

Absorption and dispersion measurements of water, D 2 O, and acetone by phase resolved PCI and OCT in the mid-infrared range 1.3μ m to 2.0 μm

We present a phase resolved partial coherence interferometer (PR-PCI) to measure absorption and dispersion of water and some other liquids. For that purpose we are investigating three different methods. In the first method we obtain spectral information of the sample by Fourier-transforming the interferometric signal. To correct for variations in scanning motor speed the interferometric signals are corrected by a signal obtained from an auxiliary He-Ne laser interferometer. The spectral information is used to calculate the absorption cross sections of several liquids like water, Deuterium oxide and acetone. The second method investigated is based on measurement of dispersion with an algorithm already introduced for differential phase contrast imaging to extract the phase information of the interferometric signal obtained by two short coherence light sources. Thereby we calculated the difference in the optical path lengths from the phase difference of the two light sources resulting from dispersion of the sample with high precision. This phase difference was used to calculate the sample dispersion. The third method is based on a differential absorption technique. The amplitude of two SLDs with different center wavelengths, one center wavelength within and one outside a water absorption band, were recorded. By measuring the difference of the amplitudes of the two signals we obtain the different extinction of the light beams when propagating through dense tissue.