Adaptive optics (AO) is used to correct ocular aberrations primarily in the cornea, lens, and tear film of every eye.
Among other applications, AO allows high lateral resolution images to be acquired with scanning laser ophthalmoscopy
(SLO) and optical coherence tomography (OCT). Spectral domain optical coherence tomography (SDOCT) is a high-speed
imaging technique that can acquire cross-sectional scans with micron-scale axial resolution at tens to hundreds of
kHz line rates. We present a compact clinical AO-SDOCT system that achieves micron-scale axial and lateral resolution
of retinal structures. The system includes a line scanning laser ophthalmscope (LSLO) for simultaneous wide-field
retinal viewing and selection of regions-of-interest. OCT and LSLO imaging and AO correction performance are
characterized. We present a case study of a single subject with hyper-reflective lesions associated with stable, resolved
central serous retinopathy to compare and contrast AO as applied to scanning laser ophthalmoscopy and optical
coherence tomography. The two imaging modes are found to be complementary in terms of information on structure
morphology. Both provide additional information lacking in the other. This preliminary finding points to the power of
combining SLO and SDOCT in a single research instrument for exploration of disease mechanisms, retinal cellular
architecture, and visual psychophysics.
Spectral domain optical coherence tomography (SDOCT) is a relatively new imaging technique that allows high-speed
cross-sectional scanning of retinal structures with little motion artifact. However, instrumentation for these systems is
not yet fast enough to collect high-density three-dimensional retinal maps free of the adverse effects of lateral eye
movements. Low coherence interferometry instruments must also contend with axial motion primarily from head
movements that shift the target tissue out of the coherence detection range. Traditional SDOCT instruments suffer from
inherent deficiencies that exacerbate the effect of depth motion, including limited range, depth-dependent signal
attenuation, and complex conjugate overlap. We present initial results on extension of our transverse retinal tracking
system to three-dimensions especially for SDOCT imagers. The design and principle of operation of two depth tracking
techniques, adaptive ranging (AR) and Doppler velocity (DV) tracking, are presented. We have integrated the threedimensional
tracking hardware into a hybrid line scanning laser ophthalmoscope (LSLO)/SDOCT imaging system.
Imaging and tracking performance was characterized by tests involving a limited number of human subjects. The hybrid
imager could switch between wide-field en-face confocal LSLO images, high-resolution cross-sectional OCT images,
and an interleaved mode of sequential LSLO and OCT images. With 3-D tracking, the RMS error for axial motion
decreased to <50 µm and for lateral motion decreased to <10 µm. The development of real-time tracking and SDOCT
image processing hardware is also discussed. Future implementation of 3-D tracking should increase the yield of usable
images and decrease the patient measurement time for clinical SDOCT systems.
In this paper we demonstrate the integration of two technologies, Line-Scanning Laser Ophthalmoscopy (LSLO) and
Spectral Domain Optical Coherence Tomography (SDOCT) into a single compact instrument that shares the same
imaging optics and line scan camera for both LSLO and OCT imaging. Co-registered high contrast wide-field en face
retinal LSLO and SDOCT images are obtained non-mydriatically with less than 600 microwatts of broadband
illumination at 15 frames/sec. The hybrid instrument can work in three different modes: LSLO mode, SDOCT mode,
and LSLO/SDOCT interleaved mode. This instrument could be useful in clinical ophthalmic diagnostics and emergency
Scanning laser ophthalmoscopy (SLO) is a powerful imaging tool with specialized applications limited to research and ophthalmology clinics due in part to instrument size, cost, and complexity. Conversely, low-cost retinal imaging devices have limited capabilities in screening, detection, and diagnosis of diseases. To fill the niche between these two, a hand-held, nonmydriatic line-scanning laser ophthalmoscope (LSLO) is designed, constructed, and tested on normal human subjects. The LSLO has only one moving part and uses a novel optical approach to produce wide-field confocal fundus images. Imaging modes include multiwavelength illumination and live stereoscopic imaging with a split aperture. Image processing and display functions are controlled with two stacked prototype compact printed circuit boards. With near shot-noise limited performance, the digital LSLO camera requires low illumination power (<500 µW) at near-infrared wavelengths. The line-scanning principle of operation is examined in comparison to SLO and other imaging modes. The line-scanning approach produces high-contrast confocal images with nearly the same performance as a flying-spot SLO. The LSLO may significantly enhance SLO utility for routine use by ophthalmologists, optometrists, general practitioners, and also emergency medical personnel and technicians in the field for retinal disease detection and other diverse applications.
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 940nm. 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.
Precise targeting of retinal structures including retinal pigment epithelial cells, feeder vessels, ganglion cells, photoreceptors, and other cells important for light transduction may enable earlier disease intervention with laser therapies and advanced methods for vision studies. A novel imaging system based upon scanning laser ophthalmoscopy (SLO) with adaptive optics (AO) and active image stabilization was designed, developed, and tested in humans and animals. An additional port allows delivery of aberration-corrected therapeutic/stimulus laser sources. The system design includes simultaneous presentation of non-AO, wide-field (~40 deg) and AO, high-magnification (1-2 deg) retinal scans easily positioned anywhere on the retina in a drag-and-drop manner. The AO optical design achieves an error of <0.45 waves (at 800 nm) over ±6 deg on the retina. A MEMS-based deformable mirror (Boston Micromachines Inc.) is used 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. Normal adult human volunteers and animals with previously-placed lesions (cynomolgus monkeys) were tested to optimize the tracking instrumentation and to characterize AO imaging performance. Ultrafast laser pulses were delivered to monkeys to characterize the ability to precisely place lesions and stimulus beams. Other advanced features such as real-time image averaging, automatic highresolution mosaic generation, and automatic blink detection and tracking re-lock were also tested. The system has the potential to become an important tool to clinicians and researchers for early detection and treatment of retinal diseases.
We have designed, developed, and tested a three-dimensional tracking and imaging system that uses a novel optical layout to acquire both en-face confocal images by scanning laser imaging (e.g. scanning laser ophthalmoscopy, SLO) and high-resolution depth sections by optical coherence tomography (OCT). The present application for this system is retinal imaging. The instrument is capable of sequentially collecting OCT and SLO images with the simple articulation of an optic affixed to a flip-mount. In addition, we have extended our mature transverse tracking system for full three-dimensional motion stabilization. The tracking component employs an innovative optical and electronic design that encodes transverse and depth tracking information on a single beam. We have demonstrated en face SLO imaging with a resolution of ~25 μm and depth-resolved OCT imaging with a resolution of ~10 μm. On artificial targets, transverse tracking was robust up to 1 m/s with a bandwidth of ~1 kHz and depth tracking was robust up to a velocity of ~15 cm/sec, a range of ~1 mm, and a bandwidth of a few hundred Hz. The details of the instrument, including optical and electronic design, are discussed. The system has the potential to provide clinicians and researchers with a wide variety of diagnostic information for the early detection and treatment of retinal diseases.
Physical Sciences Inc. (PSI) has developed an imaging sensor for remote detection of natural gas (methane) leaks. The sensor is comprised of an IR focal plane array-based camera which views the far field through a rapidly tunable Fabry-Perot interferometer. The interferometer functions as a wavelength-variable bandpass filter which selects the wavelength illuminating the focal plane array. The sensor generates 128 pixel x 128 pixel 'methane images' with a spatial resolution of 1 m (>100 x 100 pixel field-of-view). The methane column density at each pixel in the image is calculated in real time using an algorithm which estimates and compensates for line-of-sight atmospheric transmission. The compensation algorithm incorporates range-to-target as well as local air temperature and humidity. System tests conducted at 200 m standoff from sensor to leak location indicate probability of detection >90% for methane column densities >1000 ppmv-m and >2K thermal contrast between the air and the background. The probability of false alarm is <0.2% under these detection conditions.
Scanning laser ophthalmoscopy is a powerful research tool with specialized but, to date, limited use in ophthalmic clinics due in part to the size, cost, and complexity of instruments. Conversely, low-cost retinal imaging devices have limited capabilities in screening, detection, and diagnosis of diseases. To fill the niche between these two, a low-cost, hand-held, line-scanning laser ophthalmoscope (LSLO) was designed, constructed, and tested on normal human subjects. The LSLO has only one moving part, multiple imaging modes, and uses low-cost but highly sensitive complimentary metal oxide semiconductor (CMOS) linear arrays for imaging with a detector dynamic range of 12-bits. The line-scanning approach produces high contrast quasi-confocal images with nearly the same performance as a flying-spot SLO. Imaging modes include simultaneous dual wavelength illumination and live stereoscopic imaging with a split aperture. Image processing and display functions are controlled with two stacked prototype compact printed circuit boards using field-programmable gated arrays (FPGA) and other digital electronic elements. With near shot-noise limited performance, the digital LSLO camera requires low illumination power (~ 100 μW) at near-infrared wavelengths. Wide field fundus images with several imaging modes have been obtained from several human subjects. The LSLO will significantly enhance confocal scanning laser ophthalmoscopy for routine use by ophthalmologist, optometrists, general practitioners and also non-specialized emergency medical personnel and technicians in the field for retinal disease detection and other diverse applications.