We present an improved method of polarization sensitive optical coherence tomography that enables measurement and imaging of backscattered intensity, birefringence, and fast optic axis orientation simultaneously with only one single A-scan per transverse measurement location. While intensity and birefringence data are obtained in a conventional way, the optic axis orientation is determined from the phase difference recorded in two orthogonal polarization channels. We report on accuracy and precision of the method by measuring birefringence and optic axis orientation of well defined polarization states in a technical object and present maps of birefringence and, what we believe for the first time, of optic axis orientation in biological tissue.

Optical coherence tomography (OCT) has become a well established imaging tool in ophthalmology. The unprecedented depth resolution that is provided by this technique yields valuable information on different ocular tissues ranging from the anterior to the posterior eye segment. Polarization sensitive OCT (PS-OCT) extends the concept of OCT and utilizes the information that is carried by polarized light to obtain additional information on the tissue. Several structures in the eye (e.g. cornea, retinal nerve fiber layer, retinal pigment epithelium) alter the polarization state of the light and show therefore a tissue specific contrast in PS-OCT images. First this review outlines the basic concepts of polarization changing light-tissue interactions and gives a short introduction in PS-OCT instruments for ophthalmic imaging. In a second part a variety of different applications of this technique are presented in ocular imaging that are ranging from the anterior to the posterior eye segment. Finally the benefits of the method for imaging different diseases as, e.g., age related macula degeneration (AMD) or glaucoma is demonstrated.

We present a new method for identifying and segmenting the retinal pigment epithelium (RPE) in polarization sensitive optical coherence tomography (PS-OCT) images of the human retina. Contrary to previous, intensity based segmentation algorithms, our method uses an intrinsic tissue property of the RPE: its depolarizing, or polarization scrambling effect on backscattered light. Two different segmentation algorithms are presented and discussed: a simpler algorithm based on retardation data, and a more sophisticated algorithm based on local variations of the polarization state calculated from averaged Stokes vector elements. By using a state of the art spectral domain PS-OCT instrument, we demonstrate the method in healthy and diseased eyes.

We are investigating the possibility of a frequency compounding method for speckle reduction in optical coherence tomography. The method is based on incoherent summation of the magnitudes of two independent interferometric signals, which were recorded at two different center wavelengths simultaneously. We derive the corresponding statistics and compare the theoretical results with measurements obtained in a uniformly scattering sample. Finally we demonstrate our method by comparing images of human skin recorded in vivo with and without frequency compounding. The compounding method results in an increased contrast and improved image quality without loss of resolution. © 2003 Society of Photo-Optical Instrumentation Engineers.

In vivo imaging of the human retina with a resolution that allows visualization of cellular structures has proven to be essential to broaden our knowledge about the physiology of this precious and very complex neural tissue that enables the first steps in vision. Many pathologic changes originate from functional and structural alterations on a cellular scale, long before any degradation in vision can be noted. Therefore, it is important to investigate these tissues with a sufficient level of detail in order to better understand associated disease development or the effects of therapeutic intervention. Optical retinal imaging modalities rely on the optical elements of the eye itself (mainly the cornea and lens) to produce retinal images and are therefore affected by the specific arrangement of these elements and possible imperfections in curvature. Thus, aberrations are introduced to the imaging light and image quality is degraded. To compensate for these aberrations, adaptive optics (AO), a technology initially developed in astronomy, has been utilized. However, the axial sectioning provided by retinal AO-based fundus cameras and scanning laser ophthalmoscope instruments is limited to tens of micrometers because of the rather small available numerical aperture of the eye. To overcome this limitation and thus achieve much higher axial sectioning in the order of 2-5µm, AO has been combined with optical coherence tomography (OCT) into AO-OCT. This enabled for the first time in vivo volumetric retinal imaging with high isotropic resolution. This article summarizes the technical aspects of AO-OCT and provides an overview on its various implementations and some of its clinical applications. In addition, latest developments in the field, such as computational AO-OCT and wavefront sensor less AO-OCT, are covered.

We developed a high-speed polarization sensitive optical coherence tomography (PS-OCT) system for retinal imaging based on spectral domain OCT. The system uses two spectrometers, one for each polarization channel, that operate in parallel at 20000 A-lines/s each. It provides reflectivity, retardation, and cumulative optic axis orientation simultaneously. We present our instrument and discuss the requirements for the alignment of the two spectrometers specific for our setup. We show 2D spectral domain PS-OCT images and – to the best of our knowledge – the first 3D spectral domain PS-OCT data sets in form of fly-through movies and volume rendered data sets recorded in human retina in vivo.