Imaging Of Human Retina Research Articles

A new approach to optic disc detection in human retinal images using the firefly algorithm.

There are various methods and algorithms to detect the optic discs in retinal images. In recent years, much attention has been given to the utilization of the intelligent algorithms. In this paper, we present a new automated method of optic disc detection in human retinal images using the firefly algorithm. The firefly intelligent algorithm is an emerging intelligent algorithm that was inspired by the social behavior of fireflies. The population in this algorithm includes the fireflies, each of which has a specific rate of lighting or fitness. In this method, the insects are compared two by two, and the less attractive insects can be observed to move toward the more attractive insects. Finally, one of the insects is selected as the most attractive, and this insect presents the optimum response to the problem in question. Here, we used the light intensity of the pixels of the retinal image pixels instead of firefly lightings. The movement of these insects due to local fluctuations produces different light intensity values in the images. Because the optic disc is the brightest area in the retinal images, all of the insects move toward brightest area and thus specify the location of the optic disc in the image. The results of implementation show that proposed algorithm could acquire an accuracy rate of 100% in DRIVE dataset, 95% in STARE dataset, and 94.38% in DiaRetDB1 dataset. The results of implementation reveal high capability and accuracy of proposed algorithm in the detection of the optic disc from retinal images. Also, recorded required time for the detection of the optic disc in these images is 2.13s for DRIVE dataset, 2.81s for STARE dataset, and 3.52s for DiaRetDB1 dataset accordingly. These time values are average value.

Feature space optical coherence tomography based micro-angiography.

Current optical coherence tomography (OCT) based micro-angiography is prone to noise that arises from static background. This work presents a novel feature space based optical micro-angiography (OMAG) method (fsOMAG) that can effectively differentiate flow signal from static background in the feature space. fsOMAG consists of two steps. In the first step a classification map is generated that provides criterion for classification in the second step to extract functional blood flow from experimental data set. The performance of fsOMAG is examined through phantom experiments and in-vivo human retinal imaging, and compared with the existing OMAG. The results indicate its potential for clinical applications.

Application of fuzzy inference and active contour model for detection of fovea and its center in a fundus image

Detecting the center of the fovea and its boundary in a human retinal image is a challenging task due to the irregularity of the avascular foveal region. Several attempts have been made in order to detect the boundary using fluorescein angiographic images. However, no attempt was made until now in detecting the boundary of fovea directly from fundus images. In this paper, a novel method for detecting the center of the fovea and its boundary in a fundus image is proposed. A fuzzy rule-based technique has been implemented along with a gradient vector flow (GVF)-based active contour technique in order to detect the boundary of the foveal avascular zone as well as its center. The proposed method exhibits to be promising in detecting fovea regions in wide range of images.

Degree of polarization uniformity with high noise immunity using polarization-sensitive optical coherence tomography.

A new metric representing polarization uniformity is presented. Noise corrected degree of polarization uniformity (DOPU) is computed from polarization-sensitive optical coherence tomography (OCT), and selectively visualizes tissue with the multiple scattering, such as highly pigmented tissues. The new metric is designed to be minimally sensitive to systematic additive noise. The performance of this new metric is analyzed by numerical simulation and in vivo human retinal imaging, using Jones matrix OCT. The new metric exhibited only a small dependency on the signal-to-noise ratio. Selective in vivo visualization of pigmented tissues in the human retina is demonstrated, with cross sectional and en-face images.

Chemistry and biology of the initial steps in vision: the Friedenwald lecture.

Visual transduction is the process in the eye whereby absorption of light in the retina is translated into electrical signals that ultimately reach the brain. The first challenge presented by visual transduction is to understand its molecular basis. We know that maintenance of vision is a continuous process requiring the activation and subsequent restoration of a vitamin A-derived chromophore through a series of chemical reactions catalyzed by enzymes in the retina and retinal pigment epithelium (RPE). Diverse biochemical approaches that identified key proteins and reactions were essential to achieve a mechanistic understanding of these visual processes. The three-dimensional arrangements of these enzymes' polypeptide chains provide invaluable insights into their mechanisms of action. A wealth of information has already been obtained by solving high-resolution crystal structures of both rhodopsin and the retinoid isomerase from pigment RPE (RPE65). Rhodopsin, which is activated by photoisomerization of its 11-cis-retinylidene chromophore, is a prototypical member of a large family of membrane-bound proteins called G protein-coupled receptors (GPCRs). RPE65 is a retinoid isomerase critical for regeneration of the chromophore. Electron microscopy (EM) and atomic force microscopy have provided insights into how certain proteins are assembled to form much larger structures such as rod photoreceptor cell outer segment membranes. A second challenge of visual transduction is to use this knowledge to devise therapeutic approaches that can prevent or reverse conditions leading to blindness. Imaging modalities like optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) applied to appropriate animal models as well as human retinal imaging have been employed to characterize blinding diseases, monitor their progression, and evaluate the success of therapeutic agents. Lately two-photon (2-PO) imaging, together with biochemical assays, are revealing functional aspects of vision at a new molecular level. These multidisciplinary approaches combined with suitable animal models and inbred mutant species can be especially helpful in translating provocative cell and tissue culture findings into therapeutic options for further development in animals and eventually in humans. A host of different approaches and techniques is required for substantial progress in understanding fundamental properties of the visual system.

Depth-encoded all-fiber swept source polarization sensitive OCT.

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of conventional OCT and can assess depth-resolved tissue birefringence in addition to intensity. Most existing PS-OCT systems are relatively complex and their clinical translation remains difficult. We present a simple and robust all-fiber PS-OCT system based on swept source technology and polarization depth-encoding. Polarization multiplexing was achieved using a polarization maintaining fiber. Polarization sensitive signals were detected using fiber based polarization beam splitters and polarization controllers were used to remove the polarization ambiguity. A simplified post-processing algorithm was proposed for speckle noise reduction relaxing the demand for phase stability. We demonstrated systems design for both ophthalmic and catheter-based PS-OCT. For ophthalmic imaging, we used an optical clock frequency doubling method to extend the imaging range of a commercially available short cavity light source to improve polarization depth-encoding. For catheter based imaging, we demonstrated 200 kHz PS-OCT imaging using a MEMS-tunable vertical cavity surface emitting laser (VCSEL) and a high speed micromotor imaging catheter. The system was demonstrated in human retina, finger and lip imaging, as well as ex vivo swine esophagus and cardiovascular imaging. The all-fiber PS-OCT is easier to implement and maintain compared to previous PS-OCT systems and can be more easily translated to clinical applications due to its robust design.

Retinal image semi-blind deconvolution restoration based on dual tree complex transform

A combination of dual tree complex transform and the image processing algorithm of semi-blind deconvolution was proposed to eliminate the factors which make the image worse. Firstly, the retinal image obtained from the adaptive optics system was decomposed with dual tree complex transform into two parts. The low frequency image was processed by the algorithm of semi-blind deconvolution with some constraints. And the optical transfer function was used as initial parameter estimate which was constructed with the residual aberration of image system. The high frequency image was processed by denoising. Finally, the goal image was obtained by combining the processed images. The experimental results show that the retinal image quality is improved with this method, the image objective quality evaluation parameters are increased more than 5 times compared with the original image, and the average power spectrum is improved about 6 times in the spatial frequency range(70~90()-1) of retinal cells, which show that the method can contribute to satisfying the requirement of observation of human retinal image.

Real-time acquisition and display of flow contrast using speckle variance optical coherence tomography in a graphics processing unit

In this report, we describe a graphics processing unit (GPU)-accelerated processing platform for real-time acquisition and display of flow contrast images with Fourier domain optical coherence tomography (FDOCT) in mouse and human eyes in vivo. Motion contrast from blood flow is processed using the speckle variance OCT (svOCT) technique, which relies on the acquisition of multiple B-scan frames at the same location and tracking the change of the speckle pattern. Real-time mouse and human retinal imaging using two different custom-built OCT systems with processing and display performed on GPU are presented with an in-depth analysis of performance metrics. The display output included structural OCT data, en face projections of the intensity data, and the svOCT en face projections of retinal microvasculature; these results compare projections with and without speckle variance in the different retinal layers to reveal significant contrast improvements. As a demonstration, videos of real-time svOCT for in vivo human and mouse retinal imaging are included in our results. The capability of performing real-time svOCT imaging of the retinal vasculature may be a useful tool in a clinical environment for monitoring disease-related pathological changes in the microcirculation such as diabetic retinopathy.

Application of vascular bundle displacement in the optic disc for glaucoma detection using fundus images

This paper presents a methodology for glaucoma detection based on measuring displacements of blood vessels within the optic disc (vascular bundle) in human retinal images. The method consists of segmenting the region of the vascular bundle in an optic disc to set a reference point in the temporal side of the cup, determining the position of the centroids of the superior, inferior, and nasal vascular bundle segmented zones located within the segmented region, and calculating the displacement from normal position using the chessboard distance metric. The method was successful in 62 images out of 67, achieving 93.02% sensitivity, 91.66% specificity, and 91.34% global accuracy in pre-diagnosis.

Interocular correlation between human retinal images at six-weeks of age

Introduction: The developing visual system must make an appropriate vergence movement to fixate a target and permit binocular function. The visual system must plan vergence responses based on retinal images complicated by external factors (e.g. variable scene content) and developmental hurdles (e.g. immature ocular optics). Our goal was to determine the uniqueness of vergence solutions given variation in both scene structure and the optics of the developing eye.

A dual-modal retinal imaging system with adaptive optics.

An adaptive optics scanning laser ophthalmoscope (AO-SLO) is adapted to provide optical coherence tomography (OCT) imaging. The AO-SLO function is unchanged. The system uses the same light source, scanning optics, and adaptive optics in both imaging modes. The result is a dual-modal system that can acquire retinal images in both en face and cross-section planes at the single cell level. A new spectral shaping method is developed to reduce the large sidelobes in the coherence profile of the OCT imaging when a non-ideal source is used with a minimal introduction of noise. The technique uses a combination of two existing digital techniques. The thickness and position of the traditionally named inner segment/outer segment junction are measured from individual photoreceptors. In-vivo images of healthy and diseased human retinas are demonstrated.

Images of intravitreal objects projected onto posterior surface of model eye

To try to recreate the images reported by patients during vitreous surgery in a model eye. A fluid-filled model eye with a posterior frosted translucent surface which corresponded to the retina was used. Three holes were made in the model eye through which an endoillumination pipe and intraocular forceps could be inserted. A thin plastic sheet simulating an epiretinal membrane and an intraocular lens (IOL) simulating a dislocated IOL were placed on the retina. The images falling on the posterior surface were photographed from the rear. The images seen through the surgical microscope were also recorded. The images from the rear were mirror images of those seen through the surgical microscope. Intraocular instruments were seen as black shafts from the rear. When the plastic sheet was picked up, the tip of the forceps was seen more sharply on the posterior surface. The images of the dislocated IOL from the posterior were similar to that seen through the surgical microscope, including the yellow optics and blue haptics. Intravitreal objects can form images on the surface of a model eye. Objects located closer to the surface are seen more sharply, and the colour of the objects can be identified.

Multifractal Geometry in Analysis and Processing of Digital Retinal Photographs for Early Diagnosis of Human Diabetic Macular Edema

Objective: The purpose of this paper is to determine a quantitative assessment of the human retinal vascular network architecture for patients with diabetic macular edema (DME). Multifractal geometry and lacunarity parameters are used in this study.Materials and methods: A set of 10 segmented and skeletonized human retinal images, corresponding to both normal (five images) and DME states of the retina (five images), from the DRIVE database was analyzed using the Image J software. Statistical analyses were performed using Microsoft Office Excel 2003 and GraphPad InStat software.Results: The human retinal vascular network architecture has a multifractal geometry. The average of generalized dimensions (Dq) for q = 0, 1, 2 of the normal images (segmented versions), is similar to the DME cases (segmented versions). The average of generalized dimensions (Dq) for q = 0, 1 of the normal images (skeletonized versions), is slightly greater than the DME cases (skeletonized versions). However, the average of D2 for the normal images (skeletonized versions) is similar to the DME images. The average of lacunarity parameter, Λ, for the normal images (segmented and skeletonized versions) is slightly lower than the corresponding values for DME images (segmented and skeletonized versions).Conclusion: The multifractal and lacunarity analysis provides a non-invasive predictive complementary tool for an early diagnosis of patients with DME.

A Novel Approach to the Detection of Macula in Human Retinal Imagery

This paper demonstrates an approach to the rapid detection and extraction of macula from the images of human retina. For the diagnosis of ophthalmic pathologies, digital fundus images are becoming increasingly popular. This fact opens up the possibility of applying digital image processing techniques in ocular fundus images to facilitate and improve diagnosis in different ways. Macula is the major landmark for retinal fundus image registration and is indispensible for the quick understanding of retinal images. For the detection and subsequent extraction of macula, we first perform bit plane decomposition to the preprocessed image. The bit plane 0 and bit plane 1 are found to carry vital information of the location and boundary of macula. Then we locate the exact boundary by means of mathematical morphology. The proposed algorithm is computationally simple and does not require a prior knowledge of other retinal image features like optic disc or vasculature. The algorithm has been evaluated on a subset of MESSIDOR image database with various visual qualities. Robustness with respect to changes in the parameters of the algorithm has been examined.

用于自适应光学视网膜成像系统的双压电片变形反射镜

用于自适应光学视网膜成像系统的双压电片变形反射镜

Structured illumination microscopy for in-vivo human retinal imaging: a theoretical assessment

Structured illumination microscopy applied to in-vivo retinal imaging has the potential to provide a low-cost and powerful diagnostic tool for retinal disease. In this paper the key parameters that affect performance in structured illumination ophthalmoscopy are studied theoretically. These include the number of images that need to be acquired in order to generate a sectioned image, which is affected by the non-stationary nature of the retina during acquisition, the choice of spatial frequency of the illuminating sinusoid, the effect of typical ocular aberrations on axial resolution and the nature of the sinusoidal pattern produced by the illumination system. The results indicate that structured illumination ophthalmoscopy can be a robust technique for achieving axial sectioning in retinal imaging without the need for complex optical systems.

Extended depth of focus adaptive optics spectral domain optical coherence tomography

We present an adaptive optics spectral domain optical coherence tomography (AO-SDOCT) with a long focal range by active phase modulation of the pupil. A long focal range is achieved by introducing AO-controlled third-order spherical aberration (SA). The property of SA and its effects on focal range are investigated in detail using the Huygens-Fresnel principle, beam profile measurement and OCT imaging of a phantom. The results indicate that the focal range is extended by applying SA, and the direction of extension can be controlled by the sign of applied SA. Finally, we demonstrated in vivo human retinal imaging by altering the applied SA.

Vivo Human Retinal Capillary Image Mosaic on Cell-level High-resolution

Vivo Human Retinal Capillary Image Mosaic on Cell-level High-resolution

Homotopic, non-local sparse reconstruction of optical coherence tomography imagery

The resolution in optical coherence tomography imaging is an important parameter which determines the size of the smallest features that can be visualized. Sparse sampling approaches have shown considerable promise in producing high resolution OCT images with fewer camera pixels, reducing both the cost and the complexity of an imaging system. In this paper, we propose a non-local approach to the reconstruction of high resolution OCT images from sparsely sampled measurements. An iterative strategy is introduced for minimizing a homotopic, non-local regularized functional in the spatial domain, subject to data fidelity constraints in the k-space domain. The novel algorithm was tested on human retinal, corneal, and limbus images, acquired in-vivo, demonstrating the effectiveness of the proposed approach in generating high resolution reconstructions from a limited number of camera pixels.

Performance of 97-elements ALPAO membrane magnetic deformable mirror in Adaptive Optics - Optical Coherence Tomography system for in vivo imaging of human retina

We present an evaluation of two different configurations of the ALPAO 97-actuator membrane magnetic deformable mirror for wavefront correction, using either 7 or 9 actuators across the eye pupil. These tests included monitoring of aberration correction for a human subject. This AO-sub system is part of the UC Davis high-resolution human retinal imaging adaptive optics - optical coherence tomography (AO-OCT) instrument. AO-OCT allows the three-dimensional (3D) visualization of different retinal structures in vivo with high volumetric resolution (3x3x3?m 3 ). Full Text: PDF