Tracking adaptive optics scanning laser ophthalmoscope

ABSTRACT Active image stabilization for an adaptive optics scanning laser ophthalmoscope (AOSLO) was developed and tested in human subjects. The tracking device, a high speed, closed-loop optical servo which uses retinal features as tracking target, is separate from AOSLO optical path. The tracking system and AOSLO beams are combined via a dichroic beam splitter in front of the eye. The primary tracking system galvanometer mirrors follow the motion of the eye. The AOSLO raster is stabilized by a secondary set of galvanometer mirrors in the AOSLO optical train which are "slaved" to the primary mirrors with fixed scaling factors to match the angular gains of the optical systems. The AO system (at 830 nm) uses a MEMS-based deformable mirror (Boston Micromachines Inc.) for wave-front correction. The third generation retinal tracking system achieves a bandwidth of greater than 1 kHz allowing acquisition of stabilized AO images with an accuracy of <10 µm. However, such high tracking bandwidth, required for tracking saccades, results in finite tracking position noise which is evident in AOSLO images. By means of filtering algorithms, the AOSLO raster is made to follow the eye accurately with reduced tracking noise artifacts. The system design includes simultaneous presentation of non-AO, wide-field (~40 deg) live reference image captured with a line scanning laser ophthalmoscope (LSLO) typically operating from 900 to 940 nm. High-magnification (1-2 deg) AOSLO retinal scans easily positioned on the retina in a drag-and-drop manner. Normal adult human volunteers were tested to optimize the tracking instrumentation and to characterize AOSLO imaging performance. Automatic blink detection and tracking re-lock, enabling reacquisition without operator intervention, were also tested. The tracking-enhanced AOSLO may become a useful tool for eye research and for early detection and treatment of retinal diseases

Real-time processing for Fourier domain optical coherence tomography using a field programmable gate array

Real-time display of processed Fourier domain optical coherence tomography (FDOCT) images is important for applications that require instant feedback of image information, for example, systems developed for rapid screening or image-guided surgery. However, the computational requirements for high-speed FDOCT image processing usually exceeds the capabilities of most computers and therefore display rates rarely match acquisition rates for most devices. We have designed and developed an image processing system, including hardware based upon a field programmable gated array, firmware, and software that enables real-time display of processed images at rapid line rates. The system was designed to be extremely flexible and inserted in-line between any FDOCT detector and any Camera Link frame grabber. Two versions were developed for spectrometer-based and swept source-based FDOCT systems, the latter having an additional custom high-speed digitizer on the front end but using all the capabilities and features of the former. The system was tested in humans and monkeys using an adaptive optics retinal imager, in zebrafish using a dual-beam Doppler instrument, and in human tissue using a swept source microscope. A display frame rate of 27 fps for fully processed FDOCT images (1024 axial pixels×512 lateral A-scans) was achieved in the spectrometer-based systems