A sequential multi-channel OCT prototype featuring high-speed fiber optical switches to enable inter A-scan (A-scan rate: 100 kHz) sample arm switching was developed and human retinal image data is presented.
Adaptive optics (AO) is essential in order to visualize small structures such as cone and rod photoreceptors in the living human retina in vivo. By combining AO with optical coherence tomography (OCT) the axial resolution in the images can be further improved. OCT provides access to the phase of the light returning from the retina which allows a measurement of subtle length changes in the nanometer range. These occur for example during the renewal process of cone outer segments. We present an approach for measuring very small length changes using an extended AO scanning laser ophthalmoscope (SLO)/ OCT instrument. By adding a second OCT interferometer that shares the same sample arm as the first interferometer, phase sensitive measurements can be performed in the en-face imaging plane. Frame averaging decreases phase noise which greatly improves the precision in the measurement of associated length changes.
A novel approach for investigation of human retinal and choroidal blood flow by the means of multi-channel swept
source Doppler optical coherence tomography (SS-D-OCT) system is being developed. We present preliminary in vitro
measurement results for quantification of the 3D velocity vector of scatterers in a flow phantom. The absolute flow
velocity of moving scatterers can be obtained without prior knowledge of flow orientation. In contrast to previous
spectral domain (SD-) D-OCT investigations, that already proved the three-channel D-OCT approach to be suitable for
in vivo retinal blood flow evaluation, this current work aims for a similar functional approach by means of a differing
technique. To the best of our knowledge, this is the first three-channel D-OCT setup featuring a wavelength tunable laser
source. Furthermore, we present a modification of our setup allowing a reduction of the former three active illumination
channels to one active illumination channel and two passive channels, which only probe the illuminated sample. This
joint aperture (JA) approach provides the advantage of not having to divide beam power among three beams to meet
corresponding laser safety limits. The in vitro measurement results regarding the flow phantom show good agreement
between theoretically calculated and experimentally obtained flow velocity values.
We present a three beam optical Doppler tomography (ODT) technique suitable for 3-D velocity and flow measurements to evaluate total retinal blood circulation from and to the optic nerve head (ONH). The system consists of three independent ODT channels. Superluminescent diodes with a central wavelength of 840 nm and a spectral bandwidth of 50 nm were used. The sources are coupled to collimators resting in a specially designed mount to ensure a well-defined beam geometry, necessary for the full reconstruction of the three dimensional velocity vector. The reconstruction works without prior knowledge on the vessel geometry, which is normally required for ODT systems with less than three beams. The beams share a common bulk optics Michelson interferometer, while the detection comprises three identical spectrometers with a line scan rate of 50 kHz. 20 eyes of healthy volunteers were imaged with the 3 beam ODT, employing a circular scan pattern around the ONH. The mean total blood flow was calculated for arteries (47.1 ± 2.4 μl/min (mean ± SD)) and veins (47.1 ± 2.7 μl/min μl/min) independently. The two results showed no significant difference (paired t-test, p < 0.96), rendering both equally reliable for total flow measurements. Furthermore the reproducibility of the method was evaluated for the total flow and flow, velocities within each individual vessel of 6 eyes. The average variation for total flow measurements is sufficiently low to detect deviations of ~ 6% indicating high precision of the proposed method.