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Eye (London, England) Jan 2021This is a comprehensive review of the principles and applications of adaptive optics (AO) in ophthalmology. It has been combined with flood illumination ophthalmoscopy,... (Review)
Review
This is a comprehensive review of the principles and applications of adaptive optics (AO) in ophthalmology. It has been combined with flood illumination ophthalmoscopy, scanning laser ophthalmoscopy, as well as optical coherence tomography to image photoreceptors, retinal pigment epithelium (RPE), retinal ganglion cells, lamina cribrosa and the retinal vasculature. In this review, we highlight the clinical studies that have utilised AO to understand disease mechanisms. However, there are some limitations to using AO in a clinical setting including the cost of running an AO imaging service, the time needed to scan patients, the lack of normative databases and the very small size of area imaged. However, it is undoubtedly an exceptional research tool that enables visualisation of the retina at a cellular level.
Topics: Humans; Ophthalmology; Ophthalmoscopy; Optics and Photonics; Retina; Tomography, Optical Coherence
PubMed: 33257798
DOI: 10.1038/s41433-020-01286-z -
Arquivos de Neuro-psiquiatria Feb 2022Structural imaging of the brain is the most widely used diagnostic tool for investigating neurodegenerative diseases. More advanced structural imaging techniques have... (Review)
Review
Structural imaging of the brain is the most widely used diagnostic tool for investigating neurodegenerative diseases. More advanced structural imaging techniques have been applied to early or prodromic phases, but they are expensive and not widely available. Therefore, it is highly desirable to search for noninvasive, easily accessible, low-cost clinical biomarkers suitable for large-scale population screening, in order to focus on making diagnoses at the earliest stages of the disease. In this scenario, imaging studies focusing on the structures of the retina have increasingly been used for evaluating neurodegenerative diseases. The retina shares embryological, histological, biochemical, microvascular and neurotransmitter similarities with the cerebral cortex, thus making it a uniquely promising biomarker for neurodegenerative diseases. Optical coherence tomography is a modern noninvasive imaging technique that provides high-resolution two-dimensional cross-sectional images and quantitative reproducible three-dimensional volumetric measurements of the optic nerve head and retina. This technology is widely used in ophthalmology practice for diagnosing and following up several eye diseases, such as glaucoma, diabetic retinopathy and age-related macular degeneration. Its clinical impact on neurodegenerative diseases has raised enormous interest over recent years, as several clinical studies have demonstrated that these diseases give rise to reduced thickness of the inner retinal nerve fiber layer, mainly composed of retinal ganglion cells and their axons. In this review, we aimed to address the clinical utility of optical coherence tomography for diagnosing and evaluating different neurodegenerative diseases, to show the potential of this noninvasive and easily accessible method.
Topics: Humans; Neurodegenerative Diseases; Retina; Tomography, Optical Coherence
PubMed: 35352756
DOI: 10.1590/0004-282X-ANP-2021-0134 -
Redox Biology Dec 2023Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is... (Review)
Review
Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.
Topics: Antioxidants; Reactive Oxygen Species; Eye; Oxidative Stress; Lens, Crystalline
PubMed: 38006824
DOI: 10.1016/j.redox.2023.102967 -
Bioelectromagnetics Feb 2022Vitreous "floaters" are a common entoptic phenomenon that can result in significant reduction in quality of life in a proportion of sufferers. The authors use a...
Vitreous "floaters" are a common entoptic phenomenon that can result in significant reduction in quality of life in a proportion of sufferers. The authors use a computational mathematical model based on Fourier optics and reflection and transmission coefficients calculated for a planar type II collagen opacity suspended in aqueous to show that floaters are perceived by the patient through interference effects that result in significant variations in intensity on the retina when viewing a constant brightness surface. The model also predicts that backscattered intensity from floaters is ten thousand to one million times lower than the variations in intensity produced on the retina, which demonstrates that the visible effects of floaters for the patient can be highly significant, whereas clinical observation of the vitreous may be entirely unremarkable. Importantly, the results also demonstrate that floaters do not need to be opaque to cause symptoms, with only small differences in refractive index between the floater material and the surrounding vitreous needed to produce significant optical effects. The model predicts that pupil size is an important factor in determining the severity of symptoms from floaters, with constricted pupils giving much greater effect than dilated pupils. Finally, the authors' model predicts that floaters degrade contrast sensitivity function, with greatest degradation occurring in the 5-40 cycles per degree spatial frequency range and that the effects of shadowing caused by floaters are very strongly correlated to the predicted degradation of contrast sensitivity function. Bioelectromagnetics. 43:90-105, 2022. © 2021 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society.
Topics: Eye Diseases; Humans; Quality of Life; Retina; Vitreous Body
PubMed: 34969150
DOI: 10.1002/bem.22386 -
Journal of Biomedical Optics Dec 2023The assessment of biomarkers in the eye is rapidly gaining traction for the screening, diagnosis, and monitoring of ocular and neurological diseases. Targeted ocular...
SIGNIFICANCE
The assessment of biomarkers in the eye is rapidly gaining traction for the screening, diagnosis, and monitoring of ocular and neurological diseases. Targeted ocular spectroscopy is a technology that enables concurrent imaging of the eye fundus and analysis of high-quality spectra from a targeted region within the imaged area. This provides structural, compositional, and functional information of specific regions of the eye fundus from a non-invasive approach to ocular biomarker detection.
AIM
The aim of our study was to demonstrate the multimodal functionality and validation of targeted ocular spectroscopy. This was done , using a reference target and a model eye, and .
APPROACH
Images and spectra from different regions of a reference target and a model eye were acquired and analyzed to validate the system. Targeted ocular fluorescence spectroscopy was also demonstrated with the same model. Subsequently, imaging and diffuse reflectance spectra were acquired to assess blood oxygen saturation in the optic nerve head and the parafovea of healthy subjects.
RESULTS
Tests conducted with the reference target showed accurate spectral analysis within specific areas of the imaging space. In the model eye, distinct spectral signatures were observed for the optic disc, blood vessels, the retina, and the macula, consistent with the variations in tissue composition and functions between these regions. An ocular oximetry algorithm was applied to spectra from the optic nerve head and parafovea of healthy patients, showing significant differences in blood oxygen saturation. Finally, targeted fluorescence spectral analysis was performed .
CONCLUSIONS
Diffuse reflectance and fluorescence spectroscopy in specific regions of the eye fundus open the door to a whole new range of monitoring and diagnostic capabilities, from assessment of oxygenation in glaucoma and diabetic retinopathy to photo-oxidation and photodegradation in age-related macular degeneration.
Topics: Humans; Fundus Oculi; Retina; Optic Disk; Oximetry; Spectrometry, Fluorescence
PubMed: 38111476
DOI: 10.1117/1.JBO.28.12.126004 -
Acta Ophthalmologica Sep 2022To assess intrapupillary space (IPS) changes in healthy subjects with regard to decreased iris motility in patients with pseudoexfoliation glaucoma (PEXG) or...
PURPOSE
To assess intrapupillary space (IPS) changes in healthy subjects with regard to decreased iris motility in patients with pseudoexfoliation glaucoma (PEXG) or non-arteritic anterior ischaemic optic neuropathy (NAION) in a feasibility study in a clinical environment.
METHODS
Scotopic and photopic IPS measurements using three-dimensionally rendered swept-source optical coherence tomography (SS-OCT) data were obtained and compared for all subjects. Intrapupillary space (IPS) parameters were evaluated such as absolute volumetric differences, relative light response for volumetric ratios and pupillary ejection fraction (PEF) for functional contraction measurements.
RESULTS
From a total of 122 IPS from 66 subjects, 106 IPS were eligible for comparison providing values for 72 normal, 30 PEXG and 4 NAION eyes. In healthy, PEXG and NAION subjects, scotopic overall mean IPS was 8.90, 3.45 and 4.16 mm , and photopic overall mean IPS was 0.87, 0.74 and 1.13 mm , respectively. Three-dimensional contractility showed a mean absolute difference of 8.03 mm for normals (defined as 100% contractility), 2.72 mm for PEXG (33.88% of normal) and 3.03 mm for NAION (38.50% of normal) with a relative light response ratio between scotopic and photopic volumes of 10.26 (100%), 4.69 (45.70%) and 3.67 (35.78%), respectively. Pupillary ejection fraction (PEF) showed a contractile pupillary emptying of 88.11% for normals, 76.92% for PEXG and 70.91% for NAION patients.
CONCLUSION
This 3D pupillometry OCT assessment allows for quantitative measurements of pupil function, contractility and response to light. More specifically, PEF is presented as a potential (neuro)-pupillary outcome measure that could be useful in the monitoring of ophthalmic disorders that affect pupillary function.
Topics: Exfoliation Syndrome; Humans; Iris; Optic Neuropathy, Ischemic; Pupil; Tomography, Optical Coherence
PubMed: 34750988
DOI: 10.1111/aos.15063 -
Investigative Ophthalmology & Visual... May 2023To describe nonpathological myopia-related characteristics of the human eye.
PURPOSE
To describe nonpathological myopia-related characteristics of the human eye.
METHODS
Based on histomorphometric and clinical studies, qualitative and quantitative findings associated with myopic axial elongation are presented.
RESULTS
In axial myopia, the eye changes from a spherical shape to a prolate ellipsoid, photoreceptor, and retinal pigment epithelium cell density and total retinal thickness decrease, most marked in the retroequatorial region, followed by the equator. The choroid and sclera are thin, most markedly at the posterior pole and least markedly at the ora serrata. The sclera undergoes alterations in fibroblast activity, changes in extracellular matrix content, and remodeling. Bruch's membrane (BM) thickness is unrelated to axial length, although the BM volume increases. In moderate myopia, the BM opening shifts, usually toward the fovea, leading to the BM overhanging into the nasal intrapapillary compartment. Subsequently, the BM is absent in the temporal region (such as parapapillary gamma zone), the optic disc takes on a vertically oval shape, the fovea-optic disc distance elongates without macular BM elongation, the angle kappa reduces, and the papillomacular retinal vessels and nerve fibers straighten and stretch. In high myopia, the BM opening and the optic disc enlarge, the lamina cribrosa, the peripapillary scleral flange (such as parapapillary delta zone) and the peripapillary choroidal border tissue lengthen and thin, and a circular gamma and delta zone develop.
CONCLUSIONS
A thorough characterization of ocular changes in nonpathological myopia are of importance to better understand the mechanisms of myopic axial elongation, pathological structural changes, and psychophysical sequelae of myopia on visual function.
Topics: Humans; Axial Length, Eye; Myopia; Optic Disk; Choroid; Bruch Membrane
PubMed: 37126358
DOI: 10.1167/iovs.64.6.5 -
Ophthalmology Oct 2021To determine the prevalence of different types of artifacts seen in OCT angiography (OCTA) images of healthy and glaucoma eyes and evaluate the characteristics...
PURPOSE
To determine the prevalence of different types of artifacts seen in OCT angiography (OCTA) images of healthy and glaucoma eyes and evaluate the characteristics associated with poor-quality images.
DESIGN
Retrospective study.
PARTICIPANTS
A total of 649 eyes of 368 healthy, glaucoma suspect, and glaucoma patients.
METHODS
Angiovue (Optovue Inc) high-density (HD) and non-HD optic nerve head and macula OCTA images of participants were evaluated by 4 expert reviewers for the presence of different artifacts, including eye movement, defocus, shadow, decentration, segmentation error, blink, and Z offset in the superficial vascular layer. Each OCTA scan was designated to have good or poor quality based on the presence of artifacts. The association of demographic and ocular characteristics with the likelihood of obtaining poor-quality OCTA images was evaluated.
MAIN OUTCOME MEASURES
The prevalence of OCTA artifacts and the factors associated with increased likelihood of capturing poor-quality OCTA images.
RESULTS
A total of 5263 OCTA images were evaluated. Overall, 33.9% of the OCTA images had poor quality. The majority of images with acceptable quality scores (QS ≥ 4) had no artifacts (76.6%). Other images had 1 (13.6%) or 2 or more artifacts (9.8%). Older age (P < 0.001), male gender (P = 0.045), worse visual field mean deviation (P < 0.001), absence of eye tracking (P < 0.001), and macular scan area (P < 0.001) were associated with a higher likelihood of obtaining poor-quality images. In images with acceptable QS, the commercially available quality measures including QS and signal strength index had the area under the receiver operating characteristic curves of 0.65 (95% confidence interval [CI], 0.62-0.69) and 0.70 (95% CI, 0.68-0.73) to detect good-quality images, respectively.
CONCLUSIONS
OCTA artifacts associated with poor-quality images are frequent, and their prevalence is affected by ocular and patient characteristics. One should not rely solely on the quantitative assessments that are provided automatically by OCTA instruments. A systematic scan review should be conducted to ensure appropriate interpretation of OCTA images. Given the high prevalence of poor-quality OCTA images, the images should be reacquired whenever an apparent and correctable artifact is present on a captured image.
Topics: Aged; Artifacts; Female; Fluorescein Angiography; Fundus Oculi; Humans; Male; Optic Disk; Retinal Ganglion Cells; Retrospective Studies; Tomography, Optical Coherence; Visual Fields
PubMed: 33819524
DOI: 10.1016/j.ophtha.2021.03.036 -
Scientific Reports Jan 2021Due to chromatic aberration, blue images are defocused when the eye is focused to the middle of the visible spectrum, yet we normally are not aware of chromatic blur....
Due to chromatic aberration, blue images are defocused when the eye is focused to the middle of the visible spectrum, yet we normally are not aware of chromatic blur. The eye suffers from monochromatic aberrations which degrade the optical quality of all images projected on the retina. The combination of monochromatic and chromatic aberrations is not additive and these aberrations may interact to improve image quality. Using Adaptive Optics, we investigated the optical and visual effects of correcting monochromatic aberrations when viewing polychromatic grayscale, green, and blue images. Correcting the eye's monochromatic aberrations improved optical quality of the focused green images and degraded the optical quality of defocused blue images, particularly in eyes with higher amounts of monochromatic aberrations. Perceptual judgments of image quality tracked the optical findings, but the perceptual impact of the monochromatic aberrations correction was smaller than the optical predictions. The visual system appears to be adapted to the blur produced by the native monochromatic aberrations, and possibly to defocus in blue.
Topics: Color Perception; Humans; Optical Phenomena; Retina; Vision, Ocular
PubMed: 33432060
DOI: 10.1038/s41598-020-79911-w -
Experimental Eye Research Jan 2021Guinea pigs are a common model of human ocular conditions; however, their visual function has not been fully characterized. The purpose of this study was to determine...
Guinea pigs are a common model of human ocular conditions; however, their visual function has not been fully characterized. The purpose of this study was to determine the contributions of retinal ganglion cells to structural and functional measures in guinea pigs. Healthy adult guinea pigs (n = 12) underwent unilateral optic nerve crush. Retinal structure was assessed with spectral domain optical coherence tomography (OCT), and thickness of the ganglion cell/nerve fiber layer (GC/NFL) was determined. Visual function was assessed with optomotor tracking of a drifting grating and light adapted electroretinograms (ERGs). From flash ERGs, a-wave, b-wave, oscillatory potentials (OPs), and photopic negative response (PhNR) were analyzed. From pattern ERGs, N1P1 and P1N2 were analyzed. Histological studies were done at various time points for ganglion cell quantification. Optomotor tracking was absent in optic nerve crush eyes following optic nerve crush. Significant thinning of the GC/NFL was evident four weeks following the crush. Flash ERGs revealed a significant reduction in the OP1 amplitude two weeks following crush (P < 0.01) and in the PhNR amplitude six weeks following crush (P < 0.01). There were no significant changes in a-wave, b-wave, or pattern ERG responses (P > 0.05 for all). In vivo OCT imaging showed progressive thinning of inner retinal layers. Ganglion cell density, quantified histologically, was significantly reduced by 75% in the optic nerve crush eye compared to the control eye at four weeks following crush. These findings indicate that retinal ganglion cells contribute to the PhNR and OP1 components of the full field flash ERG, but not significantly to the pattern ERG in guinea pigs. This study demonstrates that OCT imaging and full field flash ERGs are valuable in assessing retinal ganglion cell loss in vivo in guinea pigs and will help to further establish the guinea pig as a model of human ocular pathologies.
Topics: Animals; Electroretinography; Guinea Pigs; Male; Nerve Crush; Nerve Fibers; Optic Nerve Injuries; Photic Stimulation; Retina; Retinal Ganglion Cells; Tomography, Optical Coherence
PubMed: 33127343
DOI: 10.1016/j.exer.2020.108339