We have developed methods which allow us to analyze images obtained with high resolution scanning laser ophthalmoscope (SLO). Registered retinal vessels can be extracted and quantified using image processing methods. Obtained data can be further analyzed for calculations of vessel morphological parameters.
We have developed a high resolution scanning laser ophthalmoscope optimized for imaging the morphology and dynamics of the retinal vessels. The system has flexible control over the imaging field of view allowing for easy navigation on the retina and selection of the desired vessel for high magnification imaging. We have also developed image processing methods that allow for extraction and quantification of vessel walls and lumen that serve for calculation of various morphological parameters.
Direct access to retinal coordinates and fine spatial and temporal resolution are clear advantages of the retinal tracking methods over widely used video-based eye trackers. Several approaches to the retinal eye tracking have been proposed so far, including frame-to-frame scanning laser ophthalmoscope (SLO) tracking, reference-frame based methods using sub-sampled frames or our MEMS-scanner-based tracker capable of measuring both fixational and saccadic eye movements. In this work we present a novel approach to the design of the retinal MEMS-based tracking system, taking advantage of two combined high-speed MEMS mirrors to form a Lissajous scanning pattern with adjustable density and framerate.
Optical coherence microscopy (OCM) facilitates imaging of biological processes in living cells with no need for fluorescence labeling and at power levels that do not harm the cells. In this paper, we present a compact full-field OCM system coupled with a commercial fluorescence microscope that allows for label-free imaging of living cells with high lateral and axial resolution. The dynamic imaging allows for the internal cell structures to be characterized based on their light scattering potential and motion dynamics. Additionally, we demonstrate that the internal motion of the cytoplasm effectively reduces the speckle noise resulting in high-contrast images.
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.
Light sensation relies on photoisomerization of chromophores in rod and cone photoreceptor cells. Spectral sensitivity of these photoreceptor cells in the retina is determined by the absorption spectra of their pigments which covers a range from 400 nm to above 700 nm. Regardless the mechanism leading to visual pigment isomerization, light sensation is triggered every time visual pigment molecules change their conformation. Thus, two-photon absorption (TPA) should produce the same result (visual sensation) as single photon absorption of light. This observation was positively verified and published by our group. During human psychophysics experiments, we found that humans can perceive light in the infrared (IR) range as colors that match half of the wavelength of the applied laser beam. Other experiments and theoretical research, such as mouse electrophysiology, biochemical studies of TPA in rhodopsin or molecular modeling studies, confirmed that visual sensation can be triggered by TPA. There are few publications describing human near infrared (NIR) perception and no formal proposals to use this phenomenon to improve ophthalmic diagnosis and monitor treatment. Here we report that the use of novel instrumentation revealed that the sensitivity threshold for NIR vision depends on age.
Scattering and fluorescence images provide complementary information about the health condition of the human eye, so getting them in a single measurement, using a single device may significantly improve a quality of diagnosis as it has been already demonstrated in Spectralis (Heidelberg Eng.) OCT instrument. There is still challenge to improve quality of fundus autofluorescence (FAF) images. The biggest obstacle in obtaining in vivo images of sufficient quality is very low fluorescence signal. For eye safety reasons, and because of patient comfort, using highpower fluorescence excitation is not an adequate solution to the low signal problem. In this contribution we show a new detection method in the retinal autofluorescence imaging, which may improve the sensitivity. We used a fast modulated (up to 500 MHz) diode laser of wavelength 473 nm and detected fluorescence in the spectral range 500-680 nm by photomultiplier and lock-in amplifier. Average power of the collimated blue beam on the cornea used for FAF measurements was set to 50 μW, 10 μW, and even 4.5 μW.
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