A optical design of confocal scanning laser ophthalmoscope based on Chinese eye model is presented, which is featured by using a Chinese eye model. Firstly, a Chinese eye model, which is obtained by reverse building from Chinese population, is adopted as eye model. Secondly, a famous optical design architecture of confocal scanning laser ophthalmoscope is selected to build our design based on the Chinese eye model. In our design, the illumination light path, the retina imaging light path, and the corneal reflection light path are all implemented. The simulation show that our design has high resolution.
SignificanceLight-sheet fluorescence microscopy (LSFM) has emerged as a powerful and versatile imaging technique renowned for its remarkable features, including high-speed 3D tomography, minimal photobleaching, and low phototoxicity. The interference light-sheet fluorescence microscope, with its larger field of view (FOV) and more uniform axial resolution, possesses significant potential for a wide range of applications in biology and medicine.AimThe aim of this study is to investigate the interference behavior among multiple light sheets (LSs) in LSFM and optimize the FOV and resolution of the light-sheet fluorescence microscope.ApproachWe conducted a detailed investigation of the interference effects among LSs through theoretical derivation and numerical simulations, aiming to find optimal parameters. Subsequently, we constructed a customized system of multi-LSFM that incorporates both interference light sheets (ILS) and noninterference light-sheet configurations. We performed beam imaging and microsphere imaging tests to evaluate the FOV and axial resolution of these systems.ResultsUsing our custom-designed light-sheet fluorescence microscope, we captured the intensity distribution profiles of both interference and noninterference light sheets (NILS). Additionally, we conducted imaging tests on microspheres to assess their imaging outcomes. The ILS not only exhibits a larger FOV compared to the NILS but also demonstrates a more uniform axial resolution.ConclusionsBy effectively modulating the interference among multiple LSs, it is possible to optimize the intensity distribution of the LSs, expand the FOV, and achieve a more uniform axial resolution.
A Hartmann-Shack wavefront sensor is designed for adaptive optics confocal scanning laser ophthalmoscopy. The Hartmann-Shack wavefront sensor designed consists of a lenslet array with square configuration, sub-aperture size 0.2mm×0.2mm , focal length 5mm and a CCD camera with pixel size 3.75μm×3.75μm.Thedynamic range and measurement accuracy of the HSWFS are simulated through the software MATLAB. Theresult of simulation indicates that focus dynamic range±14λ (λ=635nm), wavefront measurement accuracyreach RMS λ/100, all these indicators reached the requirements of the system. Finally, experimentsofcalibration by spherical wavefront were done on these indicators.
Our retinal vessel segmentation approach utilizes deep hierarchical semantic segmentation along with a closing operation. From fundus images, the retinal vessels are extracted using the supervised learning segmentation algorithm. Deep semantic segmentation that provides a hierarchical solution is adopted for rough retinal vessel segmentation. The rough segmentation results are then processed by a closing operation to refine the segmented retinal vessels. We performed experiments and comparisons with ground truths to evaluate the qualitative and quantitative effectiveness of our method. Our method effectively segments retinal vessels, as demonstrated by the experimental results.
KEYWORDS: Angiography, Image resolution, Image filtering, Gaussian filters, Current controlled current source, Signal to noise ratio, Digital filtering, Scientific research, Image quality, Denoising
Although fundus fluorescein angiography is an imaging modality that supports ophthalmic diagnosis, it requires the intravenous injection of harmful fluorescein dye. We propose the synthesis of fluorescein angiography images from fundus structure images to avoid injection. Specifically, we automatically synthesize high-resolution fundus fluorescein angiography images through an algorithm that integrates a generative adversarial networks and image stitching and enhancement. By evaluating the peak signal-to-noise ratio and structural similarity index of the proposed algorithm, pix2pix, and cycleGAN, we confirmed the superior performance of our proposal. To further validate the proposed algorithm, we compared the fundus fluorescein angiography images synthesized by our algorithm, pix2pix, and cycleGAN. The experimental results show that our algorithm provides the highest resolution and quality in the synthesis of fluorescein angiography images from fundus structure images among the evaluated methods.
We developed a clinical ophthalmic prototype by combining bimorph deformable mirror (DM)-based adaptive optics (AO) with a confocal scanning laser ophthalmoscope. A low-cost bimorph DM with a large stroke of 50 μm and an aperture of 20 mm was utilized to realize a strategy for successive AO control of aberration correction, which permitted open-loop compensation for low-order aberrations and closed-loop correction of high-order aberrations to acceptable root mean square errors of <0.08 μm in all subjects. Spherical mirrors were folded in a nonplanar configuration to minimize off-axis aberrations and provide a compact, cost-effective design, which achieved a diffraction-limited performance capable of imaging individual photoreceptor cells and blood vessels not only in healthy subjects but also in patients suffering from retinitis pigmentosa. The adaptive optics scanning laser ophthalmoscope (AOSLO) images of the diseased retina had much higher resolutions than those captured by the commercial AO fundus camera, and loss of the photoreceptor mosaic could be distinguished more accurately due to the improvement in resolution. The compact design and easy handling of the bimorph DM-based AO control may facilitate the translation of AOSLO into clinical settings, and this prototype development will continue with future device refinement and extensive clinical testing.
We design a real-time laser stimulus system for laser confocal scanning microscope. By introducing the FPGA and AOM to achieve high speed modulation of a scanning laser, we can adjust the laser lighting area freely. For reducing the size of the optical path, we use MEMS-mirror instead of traditional fast and slow axis mirrors. The size of MEMS-mirror is 1.5 mm diameter and the scanning frequencies are set 16 kHz and 12 Hz at the fast and slow axis, respectively. Our system is capable of delivering stabilized large stimulus pattern (up to 500 x 500 pixels) to the biological tissues.
Mouse is one of the most common animal models used in retinal researching, and obtaining its fundus images in vivo have significant significance for finding out formation and development mechanism of retinopathy, resolution and field-of-view are the key in fundus imaging. In this paper, we present an ophthalmoscope based on line scanning confocal technology, which utilizes one-dimension scanning line beam to increase image resolution and frame rate, it could capture mouse fundus at 1730*1730 μm field of view and 24 fps frame rate, retinal capillaries and vessels could be distinguished through reflectance and fluorescent images.
In all kinds of optical applications, the precision of central optical distance has significant influence on the desired imaging properties according to the optical design requirements. In this paper, we present a measurement method for the determination of the central distance both in assembled systems and single-lens with high precision, high speed and non-invasive characters. The distance between optical surfaces are optically measured by the mean of swept source domain interferometric system. A fiber-optics system with a central wavelength 1310 nm is built, the central distances of all surfaces within coherence length can be quickly measured at the same time. The system pixel resolution is about 0.1μm calibrated by Mitutoyo standard level-zero gauge and calculated by Fast Fourier Transform (FFT) and zero-padding algorithm. System precision double checked by other gauges is less than 0.3μm. The standard gauge-sets and a lens were measured by this system, the result also verified the high precision. The systematic error is less than 0.3μm and the sensitivity is about 22μm experimentally. The high speed swept light source (100kHz used in system) ensures the quick measuring speed. This measurement method has high precision, high speed, non-invasive and high sensitivity characters, and can be applied in related optical system.
Decorrelation-based OCTA is a widely used optical coherence tomography angiography method which utilizes OCT intensity information. However, cardiac and respiratory motions in animals are seriously degrade image quality. These kind of bulk motion is periodic, and its C-Scan (slow scan) direction component hinder motion correction because of scan position and OCT structure’s change. Some correction methods were proposed, but vasculature information will be lost when larger bulk motion occur. Here we demonstrate a correction method which uses stitch scan protocol in C-Scan direction, and sets a threshold to the maximum value of normalized cross-correlation among repeated B-Scan intensity signal to exclude false OCT B-scans. Result of In vivo imaging experiment for mice indicates that our method can reserve whole vasculature information and effectively improve image quality.
We demonstrate a home-made two-photon laser scanning microscopy (TPLSM) with a light stimulus system. In this system, the femtosecond pulses are produced by a picosecond fiber laser with pulse width compression. A laser diode serves as stimulus, which modulated by an AOM and coupled into the same light path of a femtosecond laser. The control signal of AOM and trigger signal of two scanning mirrors are synchronized by a FPGA board. With modulating the intensity of CW laser at precise point in one scanning frame, any pattern of light stimulus can be delivered to the sample in real time.
Most glaucoma surgeries involve creating new aqueous outflow pathways with the use of a small surgical instrument. This article reported a microscope-integrated, real-time, high-speed, swept-source optical coherence tomography system (SS-OCT) with a 1310-nm light source for glaucoma surgery. A special mechanism was designed to produce an adjustable system suitable for use in surgery. A two-graphic processing unit architecture was used to speed up the data processing and real-time volumetric rendering. The position of the surgical instrument can be monitored and measured using the microscope and a grid-inserted image of the SS-OCT. Finally, experiments were simulated to assess the effectiveness of this integrated system. Experimental results show that this system is a suitable positioning tool for glaucoma surgery.
A compact, high-speed line scanning quasi-confocal ophthalmoscope (LSO) for retina imaging is presented in this paper. By using a line beam to illuminate the retina, meanwhile a linear array sensor is used for imaging the retina, the LSO system significantly reduces the size, complexity, and cost comparing to a conventional confocal scanning laser ophthalmoscope (CSLO). With only one moving scanner to provide raster scanning of the line beam of the retina, the imaging frequency achieves 160 Hz and the lateral resolution is nearly 10 μm for 1024×330 pixels imaging mode. Preliminary experiments are performed for imaging the macula, the optic nerve head and other targets, providing high resolution and high speed videos of human retina.
Adaptive optics is implemented in a confocal scanning fluorescence microscope with wavefront sensorless scheme. Using the image sharpness as the optimization metric, aberration correction is performed to compensate both system- and specimen-induced aberrations by using stochastic parallel gradient descent algorithm based upon Zernike polynomial modes. In vivo vascular imaging of mice ear is completed and the results revealed the improved signal and resolution leading to in substantially enhanced image contrast with aberration correction which allowed us to detect clearer vasculature structures.
We have demonstrated adaptive correction of specimen-induced aberration during in vivo imaging of mouse bone marrow vasculature with confocal fluorescence microscopy. Adaptive optics system was completed with wavefront sensorless correction scheme based on stochastic parallel gradient descent algorithm. Using image sharpness as the optimization metric, aberration correction was performed based upon Zernike polynomial modes. The experimental results revealed the improved signal and resolution leading to a substantially enhanced image contrast with aberration correction. The image quality of vessels at 38- and 75-μm depth increased three times and two times, respectively. The corrections allowed us to detect clearer bone marrow vasculature structures at greater contrast and improve the signal-to-noise ratio.
In order to understand the relationship between accommodation and vision quality, a custom-built ultra-long scan depth spectral domain optical coherence tomography (UL-SDOCT) and a Shack-Hartmann wavefront sensor (HSWFS) were combined. The resolution and scan depth of UL-SDOCT are 6 μm and 15.6 mm, respectively, which allow for high-resolution imaging of the whole anterior segment. The HSWFS consists of a 32×32 microlens array, and is able to measure first 35th-order Zernike aberrations with (1/20)λ measurement accuracy. The integrated system succeeded in measuring the ocular anterior segment dimension parameters and the ocular monochromatic high-order aberrations simultaneously under the conditions of nonaccommodative and accommodative stimuli. This may help understand the regulatory mechanism of image quality control in the human eye.
Thirty-seven normal and primary open angle glaucoma (POAG) subjects were noninvasively imaged by a tailor-made real-time anterior segment swept source optical coherence tomography (SS-OCT) to demonstrate the differences of the Schlemm's canal (SC) between POAG and normal eyes. After the cross-section images of the anterior chamber angle were acquired by SS-OCT, SC was confirmed by two independent masked observers and the average area, long diameter, and perimeter of the SC were measured. In normal subjects the circumference, area, and long diameter is 580.34±87.81 μm, 8023.89±1486.10 μm2, and 272.83±49.39 μm, respectively, and these parameters were 393.25±98.04 μm, 3941.50±1210.69 μm2, and 190.91±46.47 μm in the POAG subjects. The area of SC in the normal ones was significantly larger than that in POAG eyes (p<0.001), so as the long diameter and the perimeter (p<0.001; p<0.001).
We introduce an automatic technique to stitch retinal images recorded with an adaptive optics confocal scanning laser ophthalmoscope (AOSLO). The AOSLO images whose field size is 1.5 deg are recorded while the fixation target is moving according to a square pattern so as to cover a wide field of view. Principal components analysis-scale invariant feature transform is used to extract and match point features of the retinal images. With the matched point features, the affine transformation is used to stitch the images to generate eight montaged images. Then, the eight images are stitched together to construct a wide-field image by a cross-correlation algorithm. An image blending algorithm is also developed to reduce seam artifacts. With the proposed algorithms, a montage whose field size is approximately 10.5×9.6 deg is constructed.
We have used anterior segment swept source optical coherence tomography to measure Schlemm’s canal (SC) morphometric values in the living human eye. Fifty healthy volunteers with 100 normal eyes were measured in the nasal and temporal side. Comparison with the published SC morphometric values of histologic sections proves the reliability of our results. The statistical results show that there are no significant differences between nasal and temporal SC with respect to their diameter, perimeter, and area in our study (diameter: t=0.122, p=0.903; perimeter: t=−0.003, p=0.998; area: t=−1.169, p=0.244); further, no significant differences in SC morphometric values are found between oculus sinister and oculus dexter (diameter: t=0.943, p=0.35; perimeter: t=1.346, p=0.18; area: t=1.501, p=0.135).
We have used an adaptive optics confocal scanning laser ophthalmoscope to assess oxygen saturation in small retinal vessels. Images of the vessels with a diameter smaller than 50 μm are recorded at oxygen sensitive and isosbestic wavelengths (680 and 796 nm, respectively). The vessel optical densities (ODs) are determined by a computer algorithm. Then, OD ratios (ODRs), which are inversely proportional to oxygen saturation, are calculated. The results show that arterial ODRs are significantly smaller than venous ODRs, indicating that oxygen saturation in the artery is higher than that in the vein. To the best of our knowledge, this is the first noninvasive measurement of oxygen saturation in small retinal vessels.
The optical design of a confocal scanning laser ophthalmoscope based on adaptive optics (AOSLO) is described in
this paper. Spherical mirrors are used for pupil relay and astigmatism compensation. The main optical system
achieves diffraction-limited performance through the entire scanning angle (6mm pupil, 3 degree on pupil plane).
When optical coherence tomography (OCT) is used to image human retina, its lateral resolution is deteriorated by the
aberrations of the human eye. To get over this disadvantage, a high-resolution imaging system combining OCT with
adaptive optics (AO) is being developed. The AO system consists of a 61-element deformable mirror and a 16×16 array
Shack-Hartmann wave front sensor. In this paper, the configuration of the AO/OCT system is described, and the
simulation results and the static aberration analysis of AO/OCT systems are presented.
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