We present a novel platform for eye tracking showing high speed and accuracy in a wide range of realizable visual tasks. The optical setup consists of the scanning laser ophthalmoscope, the actual tracker (the FreezEye Tracker), and a visual projector for task presentation. The MEMS-based tracker scans the retina with a framerate of 1.24 kHz, providing high angular and temporal resolution. Advanced algorithms allow for precise reconstruction of the eye trajectory covering the range of movements from small microsaccades to high amplitude saccades. The high quality of the generated data provides an abundance of data potentially useful for diagnostic purposes.
Neurodegenerative diseases, such as multiple sclerosis (MS), negatively impact the aging global population. MS damage various parts of the central nervous system, leading to various eye-movement abnormalities. We have built a retinal FreezEye Tracker (FET) to measure a wide dynamic range of eye movements of up to 10 degrees with an ultrahigh temporal and spatial resolution during visual tasks, including fixations, experiments with saccades, and smooth pursuit. To compare, we performed the same experiments with pupil tracker EyeLink 1000. The amplitudes of detected saccades are similar in both devices, but FET provides high-resolution details on eye trajectory during fixation periods.
Limited angle optical diffraction tomography (ODT) is a 3D quantitative phase imaging method that allows to retrieve information about 3D refractive index (RI) distribution of live, unlabeled biosamples. The main limitation of this method is that its common transmission configuration results in very low axial resolution. On the other hand, optical coherence tomography (OCT), working in its most popular reflection configuration retrieves information about the gradient of the RI of investigated samples. However, the results are of qualitative nature. Moreover, due to low numerical aperture of the objective lens typically used in OCT systems, the resolution is high in the axial direction and relatively low in transverse direction. From the point of view of K-space filling, these two imaging modalities are complementary. Here we present a method of combining ODT projections with OCT scans. The combined technique, called optical coherence diffraction tomography (OCDT) operates in transflective mode, where ODT is captured in transmission and OCT in reflection. Theory behind conversion of OCT scans into ODT projections is given. With the use of numerical simulations we show what enhancement can be obtained when OCT and ODT data are combined directly. Also, experimental verification is presented.
Constructing an image acquired by a non-uniform scanning pattern is a difficult task. The main challenges are:(1) resampling technique (2) discrepancy between demanded (dictated by control signal) and actually performed, empirical scanning path. Here, we show how to calibrate the scanning path of MEMS scanner using Galvanometric Scanner and to what extent the time of acquisition impacts the resulting image.
The eye motion is broadly considered as a valuable source of information in the fields related to psychology, neuroscience and neurology. Therefore, quantitative characterization of eye tracker data is an important task. Saccades are sigmoidal, ballistic movements that in particular deserve more attention due to their complex shape and natural diversity. We have developed the high accuracy model of saccades and microsaccades of mean absolute error equal to 0.0104 degree on average. We present the methodology for extraction of saccadic features using this model and show the potential of the method in biometric experiments.
Full-field swept-source optical coherence tomography (FF-SS-OCT) provides high-resolution depth-resolved images by parallel Fourier-domain interferometric detection. Traditionally, FF-SS-OCT suffers from the cross-talk-generated noise from spatially coherent lasers. This noise reduces the image quality and limits wide adaptation of FF-SS-OCT for practical and clinical applications. To tackle this problem, we demonstrate and implement the spatiotemporal optical coherence (STOC) manipulation. In STOC, the phase of light in one of the interferometer arm is modulated in time with inhomogeneous phase masks displayed sequentially on the SLM. This modulation is synchronized with light acquisition to effectively control the spatial coherence of the detected light. A term "effectively" means that we do not generate the secondary source with imposed coherence properties (e.g. spatial incoherence). Instead the idea is to tailor the incident light to constrict the region of high fringe visibility to the spatial extents individual detection channels. Hence, SLM pixels are grouped into small blocks of uniform phase shifts. Then, phases are varied in time to modulate the light incident on the sample. By matching the dimensions of the SLM blocks to spatial extents of detection channels, we can de-correlate light from each channel. The unwanted interference between channels is washed-out and the cross-talk-generated noise is suppressed, helping to improve image quality. Here, the STOC approach is validated by imaging 1951 USAF resolution test chart covered by diffuser, scattering phantom and the rat skin ex vivo. Our results show a promising enhancement of the FF-SS-OCT capabilities that can be beneficial for imaging biological samples.
Optical imaging of biological samples or living tissue structures requires light delivery to a region of interest and then collection of scattered light or fluorescent light in order to reconstruct an image of the object. When the coherent illumination light enters bulky biological object, each of scattering center (single molecule, group of molecules or other sample feature) acts as a secondary light source. As a result, scattered spherical waves from these secondary sources interact with each other, generating cross-talk noise between optical channels (eigenmodes). The cross-talk effect have serious impact on the performance of the imaging systems. In particular it reduces an ability of optical system to transfer high spatial frequencies thereby reducing its resolution. In this work we present a fast method to eliminate all unwanted waves combination, that overlap at image plane, suppressing recovery of high spatial frequencies by using the spatio-temporal optical coherence manipulation (STOC, [1]). In this method a number of phase mask is introduced to illuminating beam by spatial light modulator in a time of single image acquisition. We use a digital mirror device (DMD) in order to rapid cross-talk noise reduction (up to 22kHz modulation frequency) when imaging living biological cells in vivo by using full-field microscopy setup with double pass arrangement. This, to our best knowledge, has never been shown before.
[1] D. Borycki, M. Nowakowski, and M. Wojtkowski, Opt. Lett. 38, 4817 (2013).
We present an optical design and describe the way to build and test a new model of the human eye. This model is
intended to work specifically with wide field angles featuring invariant aberrations across the field. Our model is a
compromise between the simplicity of the design (using only two
plano-convex lenses) and its ability to imitate the real
properties of ocular aberrations. The position of the aperture stop in the system as well as the concentricity of the first
and the last surfaces allowed us to control the field aberrations. We model the artificial eye using the optical design
software Zemax. Our ray-tracing analysis and experimental results are discussed in relation to the inverse optical design,
which enables us to find the imperfections in the artificial eye with interferometric testing. Measuring wavefront
aberrations in double pass on axis we could identify the manufacturing errors in lens characteristics as well as find their
misalignment errors. The inverse optical design involves modification of the original eye model parameters (thickness,
radius of curvatures, asphericity, lens centration and tilts) to match the experimental measurements of the wavefront
aberrations. We identified the sources of errors and verified that the overall performance of the artificial eye is
comparable with the theoretical wide-field eye model, which is based on the average properties of the real human eye.
It is well known that manufacturing of lens systems featuring concentric design is a difficult task mainly due to nontrivial
testing required for optical surfaces sharing their center of curvature. We propose an inexpensive imaging
method, which can be used to test the alignment, concentricity, the axial length of air gaps and figure errors of the optical
surfaces in concentric lens systems. Our setup consists of a laser, collimating lenses, a beam splitter, testing and imaging
arms. We demonstrate the functionality of this scheme by testing an artificial eye with concentric design. During the
experiment, the laser beam travels along the optical axis of the testing arm until it is focused onto the surfaces of the
artificial eye. The light is then reflected and directed into the imaging arm to the camera. We perform tests in two
positions: first, when the focused beam hits the vertex of the convex lens of the eye, and second, when the light comes
into the system perpendicular to the optical surfaces. By finding the distance between these two positions, we can obtain
the radius of curvature of the lens surfaces. In addition, the images formed on the camera give us accurate information
about the alignment and the quality of the optical system under the test. Our results also show that this method is a
powerful technique to determine the position of air gaps in compound optical systems.
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