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Son T, Ma G, Yao X. Functional OCT reveals anisotropic changes of retinal flicker-evoked vasodilation. OPTICS LETTERS 2024; 49:2121-2124. [PMID: 38621091 DOI: 10.1364/ol.520840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Accepted: 03/18/2024] [Indexed: 04/17/2024]
Abstract
The purpose of this study is to verify the effect of anisotropic property of retinal biomechanics on vasodilation measurement. A custom-built optical coherence tomography (OCT) was used for time-lapse imaging of flicker stimulation-evoked vessel lumen changes in mouse retinas. A comparative analysis revealed significantly larger (18.21%) lumen dilation in the axial direction compared to the lateral (10.77%) direction. The axial lumen dilation predominantly resulted from the top vessel wall movement toward the vitreous direction, whereas the bottom vessel wall remained stable. This observation indicates that the traditional vasodilation measurement in the lateral direction may result in an underestimated value.
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2
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Aung MH, Aleman TS, Garcia AS, McGeehan B, Ying GS, Avery RA. Stimulus type and duration affect magnitude and evolution of flicker-induced hyperemia measured by laser speckle flowgraphy at the optic disc and peripapillary vessels. Sci Rep 2024; 14:6659. [PMID: 38509194 PMCID: PMC10954713 DOI: 10.1038/s41598-024-57263-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2023] [Accepted: 03/15/2024] [Indexed: 03/22/2024] Open
Abstract
Neurovascular coupling is a vital mechanism employed by the cerebrovascular system, including the eye, to regulate blood flow in periods of neuronal activation. This study aims to investigate if laser speckle flowgraphy (LSFG) can detect coupling response elicited by flickering light stimuli and how variations in stimulus type and duration can affect the magnitude and evolution of blood flow in the optic nerve head (ONH) and peripapillary vessels. Healthy adults were exposed to two types of 10-Hz flicker stimuli: a photopic negative response-like stimulus (PhNR-S) or a visual evoked potential-like stimulus (VEP-S)-each presented in separate 10- and 60-s epochs. Both PhNR-S and VEP-S significantly increased ONH blood flow (p < 0.001) immediately after flicker cessation, with a trend of 60-s stimuli (PhNR-S = 11.6%; VEP-S = 10.4%) producing a larger response than 10-s stimuli (PhNR-S = 7.5%; VEP-S = 6.2%). Moreover, exposure to 60-s stimuli elicited a significantly prolonged ONH hyperemic response, especially with PhNR-S. Lastly, stimulation with either 60-s stimuli elicited a robust increase in blood flow within the peripapillary arterioles (p < 0.01) and venules (p < 0.01) as well. Flicker stimulation with common visual electrophysiology stimuli (PhNR-S and VEP-S) induced a demonstrable increase in ONH and peripapillary vessel blood flow, which varied with flicker duration. Our results validate that LSFG is a robust method to quantify flicker-induced hyperemic responses and to study neurovascular coupling in humans.
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Affiliation(s)
- Moe H Aung
- Departments of Neurology, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.
- Department of Ophthalmology, Dell Medical School at The University of Texas at Austin, Austin, TX, USA.
| | - Tomas S Aleman
- Department of Ophthalmology, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
- Division of Ophthalmology, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Arielle S Garcia
- Division of Ophthalmology, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Brendan McGeehan
- Department of Ophthalmology, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Gui-Shuang Ying
- Department of Ophthalmology, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Robert A Avery
- Departments of Neurology, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
- Department of Ophthalmology, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
- Division of Ophthalmology, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
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3
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Böhm EW, Pfeiffer N, Wagner FM, Gericke A. Methods to measure blood flow and vascular reactivity in the retina. Front Med (Lausanne) 2023; 9:1069449. [PMID: 36714119 PMCID: PMC9877427 DOI: 10.3389/fmed.2022.1069449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 12/23/2022] [Indexed: 01/14/2023] Open
Abstract
Disturbances of retinal perfusion are involved in the onset and maintenance of several ocular diseases, including diabetic retinopathy, glaucoma, and retinal vascular occlusion. Hence, knowledge on ocular vascular anatomy and function is highly relevant for basic research studies and for clinical judgment and treatment. The retinal vasculature is composed of the superficial, intermediate, and deep vascular layer. Detection of changes in blood flow and vascular diameter especially in smaller vessels is essential to understand and to analyze vascular diseases. Several methods to evaluate blood flow regulation in the retina have been described so far, but no gold standard has been established. For highly reliable assessment of retinal blood flow, exact determination of vessel diameter is necessary. Several measurement methods have already been reported in humans. But for further analysis of retinal vascular diseases, studies in laboratory animals, including genetically modified mice, are important. As for mice, the small vessel size is challenging requiring devices with high optic resolution. In this review, we recapitulate different methods for retinal blood flow and vessel diameter measurement. Moreover, studies in humans and in experimental animals are described.
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Swiatczak B, Schaeffel F, Calzetti G. Imposed positive defocus changes choroidal blood flow in young human subjects. Graefes Arch Clin Exp Ophthalmol 2023; 261:115-125. [PMID: 36171460 PMCID: PMC9803748 DOI: 10.1007/s00417-022-05842-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 07/26/2022] [Accepted: 09/20/2022] [Indexed: 01/19/2023] Open
Abstract
PURPOSE It has previously been found that imposing positive defocus changes axial length and choroidal thickness after only 30 min. In the present study, we investigated whether these changes may result from an altered choroidal blood flow. METHODS Eighteen young adult subjects watched a movie from a large screen (65 in.) in a dark room at 2 m distance. A 15-min wash-out period was followed by 30 min of watching the movie with a monocular positive defocus (+ 2.5D). Changes in axial length and ocular blood flow were measured before and after the defocus, by using low-coherent interferometer (LS 900, Haag-Streit, Switzerland) and a laser speckle flowgraphy (LSFG) RetFlow unit (Nidek Co., LTD, Japan), respectively. Three regions were analyzed: (1) the macular area, where choroidal blood flow can be measured, (2) the optic nerve head (ONH), and (3) retinal vessel segments. RESULTS Changes in choroidal blood flow were significantly and negatively correlated with changes in axial length that followed positive defocus in exposed eyes (R = - 0.67, p < 0.01). The absolute values of changes in choroidal blood flow in the defocused eyes were significantly larger than in the fellow control eyes (2.35 ± 2.16 AU vs. 1.37 ± 1.44 AU, respectively, p < 0.05). ONH and retinal blood flow were not associated with the induced changes in axial length. CONCLUSIONS Positive defocus selectively alters choroidal, but not retinal or ONH blood flow in young human subjects after short-term visual exposure. The results suggest that blood flow modulation is involved in the mechanism of choroidal responses to optical defocus.
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Affiliation(s)
- Barbara Swiatczak
- grid.508836.0Institute of Molecular and Clinical Ophthalmology Basel (IOB), Mittlere Strasse 91, 4056 Basel, Switzerland
| | - Frank Schaeffel
- grid.508836.0Institute of Molecular and Clinical Ophthalmology Basel (IOB), Mittlere Strasse 91, 4056 Basel, Switzerland ,grid.10392.390000 0001 2190 1447Section of Neurobiology of the Eye, Ophthalmic Research Institute, University of Tuebingen, Tuebingen, Germany ,grid.10392.390000 0001 2190 1447Zeiss Vision Lab, Ophthalmic Research Institute, University of Tuebingen, Tuebingen, Germany
| | - Giacomo Calzetti
- grid.508836.0Institute of Molecular and Clinical Ophthalmology Basel (IOB), Mittlere Strasse 91, 4056 Basel, Switzerland ,grid.6612.30000 0004 1937 0642Department of Ophthalmology, University of Basel, Basel, Switzerland ,grid.10383.390000 0004 1758 0937Department of Ophthalmology, University of Parma, Parma, Italy
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5
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Hanssen H, Streese L, Vilser W. Retinal vessel diameters and function in cardiovascular risk and disease. Prog Retin Eye Res 2022; 91:101095. [PMID: 35760749 DOI: 10.1016/j.preteyeres.2022.101095] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Revised: 06/03/2022] [Accepted: 06/13/2022] [Indexed: 12/13/2022]
Abstract
In the last two decades evidence has gradually accumulated suggesting that the eye may be a unique window for cardiovascular risk stratification based on the assessment of subclinical damage of retinal microvascular structure and function. This can be facilitated by non-invasive analysis of static retinal vessel diameters and dynamic recording of flicker light-induced and endothelial function-related dilation of both retinal arterioles and venules. Recent new findings have made retinal microvascular biomarkers strong candidates for clinical implementation as reliable risk predictors. Beyond a review of the current evidence and state of research, the article aims to discuss the methodological benefits and pitfalls and to identify research gaps and future directions. Above all, the potential use for screening and treatment monitoring of cardiovascular disease risk are highlighted. The article provides fundamental comprehension of retinal vessel imaging by explaining anatomical and physiological essentials of the retinal microcirculation leading to a detailed description of the methodological approach. This allows for better understanding of the underlying retinal microvascular pathology associated with the prevalence and development of cardiovascular disease. A body of new evidence is presented on the clinical validity and predictive value of retinal vessel diameters and function for incidence cardiovascular disease and outcome. Findings in children indicate the potential for utility in childhood cardiovascular disease prevention, and the efficacy of exercise interventions highlight the treatment sensitivity of retinal microvascular biomarkers. Finally, coming from the availability of normative data, solutions for diagnostic challenges are discussed and conceptual steps towards clinical implementation are put into perspective.
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Affiliation(s)
- Henner Hanssen
- Department of Sport, Exercise and Health, Preventive Sports Medicine and Systems Physiology, Medical Faculty, University of Basel, Switzerland.
| | - Lukas Streese
- Department of Sport, Exercise and Health, Preventive Sports Medicine and Systems Physiology, Medical Faculty, University of Basel, Switzerland
| | - Walthard Vilser
- Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, Ilmenau, Germany; Neonatology and Pediatric Intensive Care Unit, Department of Pediatrics, Jena University Hospital, Jena, Germany
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6
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Lal A, Dave N, Barry MA, Sood A, Mitchell P, Thiagalingam A. A stronger association of diabetes mellitus with impaired hyperaemia using a novel ECG-gated device compared with peripheral arterial tonometry. Int Ophthalmol 2022; 42:2855-2869. [PMID: 35672599 PMCID: PMC9420096 DOI: 10.1007/s10792-022-02276-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2021] [Accepted: 03/12/2022] [Indexed: 11/28/2022]
Abstract
PURPOSE Impaired digital reactive hyperaemia and flicker-stimulated retinal vascular response are commonly reported risk markers of cardiovascular disease. This is the first study to determine the correlation of these risk markers with diabetes mellitus by comparing our novel flicker-modulated ECG-gated fundoscope with the EndoPAT2000 system. METHODS In total, 119 controls and 120 participants with diabetes mellitus partook in this cross-sectional study. The EndoPAT2000 system assessed digital reactive hyperaemia under fasting conditions. A mydriatic ECG-gated fundoscope with a novel flicker module acquired digital retinal images of the left eye before, during and after flicker stimulation. An inhouse semi-automated software measured retinal vessel diameters using a validated protocol with two observers repeating measurements in a subset of 10 controls and 10 participants with diabetes mellitus. Intra- and inter-observer reliability analyses occurred by the interclass correlation coefficient. A receiver operating characteristic curve established associations of variables with diabetes mellitus. RESULTS Diabetes mellitus was more strongly associated with flicker-stimulated retinal arteriolar calibre change from baseline (AUC 0.81, 95% CI 0.75-0.87, p < 0.0001) than reactive hyperaemia index. Median flicker-stimulated arteriolar calibre change from baseline (controls: 2.74%, IQR 1.07 vs diabetes mellitus: 1.64%, IQR 1.25, p < 0.0001) and reactive hyperaemia index (controls: 1.87, IQR 0.81 vs diabetes mellitus: 1.60, IQR 0.81, p = 0.003) were lower in diabetes mellitus than controls. Intra- and inter-observer reliability coefficients were high from 0.87 to 0.93. CONCLUSIONS Impaired flicker-stimulated retinal arteriolar calibre change from baseline is more highly correlated with diabetes mellitus in this study than a reduced reactive hyperaemia index.
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Affiliation(s)
- Anchal Lal
- Department of Cardiology, Westmead Hospital, Sydney, NSW, Australia, 2145. .,Sydney Medical School (Westmead Clinical School), The University of Sydney, Sydney, NSW, Australia, 2145. .,Centre for Vision Research, Westmead Institute for Medical Research, Sydney, NSW, Australia, 2145. .,Department of Cardiology, Room 2082, Level 2, Clinical Sciences Corridor, Westmead Hospital, Cnr Darcy and Hawkesbury Roads, Westmead, Sydney, NSW, Australia, 2145.
| | - Neha Dave
- School of Medicine and Public Health, The University of Newcastle, Callaghan, NSW, Australia, 2308
| | | | - Annika Sood
- Department of Cardiology, Westmead Hospital, Sydney, NSW, Australia, 2145
| | - Paul Mitchell
- Sydney Medical School (Westmead Clinical School), The University of Sydney, Sydney, NSW, Australia, 2145.,Centre for Vision Research, Westmead Institute for Medical Research, Sydney, NSW, Australia, 2145
| | - Aravinda Thiagalingam
- Department of Cardiology, Westmead Hospital, Sydney, NSW, Australia, 2145.,Sydney Medical School (Westmead Clinical School), The University of Sydney, Sydney, NSW, Australia, 2145
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7
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Pappelis K, Jansonius NM. Retinal Oxygen Delivery and Extraction in Ophthalmologically Healthy Subjects With Different Blood Pressure Status. Transl Vis Sci Technol 2022; 11:9. [PMID: 35119472 PMCID: PMC8819358 DOI: 10.1167/tvst.11.2.9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose To compare retinal oxygen delivery (DO2) and oxygen extraction (VO2) in ophthalmologically healthy subjects with different blood pressure (BP) status. Methods In this case-control study, we prospectively included 93 eyes of 93 subjects (aged 50-65 years) from a Dutch cohort (n = 167,000) and allocated them to four groups (low BP, normal BP [controls], treated arterial hypertension [AHT], untreated AHT). We estimated vascular calibers from fundus images and fractal dimension from optical coherence tomography angiography scans. We combined calibers, fractal dimension, BP, and intraocular pressure measurements in a proxy of retinal blood flow (RBF), using a Poiseuille-based model. We measured arterial and venous oxygen saturations (SaO2, SvO2) with a scanning laser ophthalmoscope. We calculated the DO2 and VO2 from the RBF, SaO2, and SvO2. We compared the DO2 and VO2 between groups and investigated the DO2-VO2 association. Results DO2 and VO2 were different between groups (P = 0.009, P = 0.036, respectively). In a post hoc analysis, the low BP group had lower DO2 than the untreated AHT group (P = 4.9 × 10-4). The low BP group and the treated AHT group had a lower VO2 than the untreated AHT group (P = 0.021 and P = 0.034, respectively). There was a significant DO2-VO2 correlation (Robs = 0.65, bobs = 0.51, P = 2.4 × 10-12). After correcting for shared measurement error, the slope was not significant. Conclusions The DO2 and VO2 were altered in ophthalmologically healthy subjects with different BP status. Future studies could elucidate whether these changes can explain the increased risk of ophthalmic pathologies in those subjects. Translational Relevance Understanding the baseline interplay between BP, retinal perfusion, and oxygenation allows for improved evaluation of retinal disease manifestation.
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Affiliation(s)
- Konstantinos Pappelis
- Department of Ophthalmology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.,Graduate School of Medical Sciences (Research School of Behavioural and Cognitive Neurosciences), University of Groningen, Groningen, the Netherlands
| | - Nomdo M Jansonius
- Department of Ophthalmology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.,Graduate School of Medical Sciences (Research School of Behavioural and Cognitive Neurosciences), University of Groningen, Groningen, the Netherlands
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8
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Warner RL, Gast TJ, Sapoznik KA, Carmichael-Martins A, Burns SA. Measuring Temporal and Spatial Variability of Red Blood Cell Velocity in Human Retinal Vessels. Invest Ophthalmol Vis Sci 2021; 62:29. [PMID: 34846516 PMCID: PMC8648047 DOI: 10.1167/iovs.62.14.29] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose The retinal circulation regulates blood flow through various internal and external factors; however, it is unclear how locally these factors act within the retinal microcirculation. We measured the temporal and spatial variability of blood velocity in small retinal vessels using a dual-beam adaptive optics scanning laser ophthalmoscope. Methods In young healthy subjects (n = 3), temporal blood velocity variability was measured in a local vascular region consisting of an arteriole, capillary, and venule repeatedly over 2 days. Data consisted of 10 imaging periods separated into two sessions: (1) five 6-minute image acquisition periods with 30-minute breaks, and (2) five 6-minute image acquisition periods with 10-minute breaks. In another group of young healthy subjects (n = 5), spatial distribution of velocity variability was measured by imaging three capillary segments during three 2-minute conditions: (1) baseline imaging condition (no flicker), (2) full-field flicker, and (3) no flicker condition again. Results Blood velocities were measurable in all subjects with a reliability of about 2%. The coefficient of variation (CV) was used as an estimate of the physiological variability of each vessel. Over 2 days, the average CV in arterioles was 7% (±2%); in capillaries, it was 19% (±6%); and, in venules, it was 8% (±2%). During flicker stimulation, the average capillary CV was 16% during baseline, 15% during flicker stimulation, and 18% after flicker stimulation. Conclusions Capillaries in the human retina exhibit spatial and temporal variations in blood velocity. This inherent variation in blood velocity places limits on studying the vascular regulation of individual capillaries, and the study presented here serves as a foundation for future endeavors.
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Affiliation(s)
- Raymond L Warner
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Thomas J Gast
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Kaitlyn A Sapoznik
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | | | - Stephen A Burns
- School of Optometry, Indiana University, Bloomington, Indiana, United States
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Nian S, Lo ACY, Mi Y, Ren K, Yang D. Neurovascular unit in diabetic retinopathy: pathophysiological roles and potential therapeutical targets. EYE AND VISION 2021; 8:15. [PMID: 33931128 PMCID: PMC8088070 DOI: 10.1186/s40662-021-00239-1] [Citation(s) in RCA: 47] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Accepted: 04/02/2021] [Indexed: 02/06/2023]
Abstract
Diabetic retinopathy (DR), one of the common complications of diabetes, is the leading cause of visual loss in working-age individuals in many industrialized countries. It has been traditionally regarded as a purely microvascular disease in the retina. However, an increasing number of studies have shown that DR is a complex neurovascular disorder that affects not only vascular structure but also neural tissue of the retina. Deterioration of neural retina could precede microvascular abnormalities in the DR, leading to microvascular changes. Furthermore, disruption of interactions among neurons, vascular cells, glia and local immune cells, which collectively form the neurovascular unit, is considered to be associated with the progression of DR early on in the disease. Therefore, it makes sense to develop new therapeutic strategies to prevent or reverse retinal neurodegeneration, neuroinflammation and impaired cell-cell interactions of the neurovascular unit in early stage DR. Here, we present current perspectives on the pathophysiology of DR as a neurovascular disease, especially at the early stage. Potential novel treatments for preventing or reversing neurovascular injuries in DR are discussed as well.
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Affiliation(s)
- Shen Nian
- Department of Pathology, Xi'an Medical University, Xi'an, Shaanxi Province, China.
| | - Amy C Y Lo
- Department of Ophthalmology, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong, Hong Kong
| | - Yajing Mi
- Institute of Basic Medicine Science, Xi'an Medical University, Xi'an, Shaanxi Province, China
| | - Kai Ren
- Department of Biochemistry and Molecular Biology, Xi'an Medical University, Xi'an, Shaanxi Province, China
| | - Di Yang
- Department of Ophthalmology, First Affiliated Hospital of Kunming Medical University, Kunming Medical University, Kunming, Yunnan Province, China.
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Bek T, Jeppesen SK. Reduced Oxygen Extraction in the Retinal Periphery When the Arterial Blood Pressure Is Increased by Isometric Exercise in Normal Persons. Invest Ophthalmol Vis Sci 2021; 62:11. [PMID: 33683296 PMCID: PMC7960864 DOI: 10.1167/iovs.62.3.11] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Purpose Recent evidence suggests that the smaller retinal vessels are significantly involved in the regulation of retinal blood flow and that this regulation may differ among the macular area and the retinal periphery. An alternative to studying blood flow regulation in smaller retinal vessels that are difficult to resolve is to assess the metabolic consequences of changes in the microcirculation using oximetry. Methods In 20 normal persons aged (mean ± SD, range) 30.1 ± 3.8 (24–37) years, the oxygen saturation and diameter of retinal arterioles and venules to the macular area and the retinal periphery were studied before and during an increase in the arterial blood pressure induced by isometric exercise. Results The isometric exercise increased the mean arterial blood pressure by (mean ± SEM) 10.0 ± 1.1 mm Hg but induced no significant changes in the diameter of the arterioles (P = 0.83). The isometric exercise had no significant effect on the oxygen saturation in the arterioles supplying the macular area and the retinal periphery (P > 0.42 for both comparisons). However, there was a significant increase in the oxygen saturation in venules draining the retinal periphery to reduce the oxygen extraction from (mean ± SEM) 36.0% ± 2.3% to 30.6% ± 2.1% (P = 0.002) but no significant change in the preexisting low oxygen extraction in the macular area that changed from (mean ± SEM) 18.2% ± 3.0% to 16.2% ± 1.9% (P = 0.37). Conclusions Minor changes in the arterial blood pressure can induce changes in retinal rheology with significant regional variation. The finding may help explain regional variations in manifestations of retinal vascular disease such as hyperpermeability in the macular area and capillary occlusion in the retinal periphery.
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Affiliation(s)
- Toke Bek
- Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark
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11
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Kallab M, Hommer N, Tan B, Pfister M, Schlatter A, Werkmeister RM, Chua J, Schmidl D, Schmetterer L, Garhöfer G. Plexus-specific effect of flicker-light stimulation on the retinal microvasculature assessed with optical coherence tomography angiography. Am J Physiol Heart Circ Physiol 2020; 320:H23-H28. [PMID: 33275537 DOI: 10.1152/ajpheart.00495.2020] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In neural tissues, the coupling between neural activity and blood flow is a physiological key principle in blood flow regulation. We used optical coherence tomography angiography to investigate stimulus-evoked hemodynamic responses in different microvascular layers of the human retina. Twenty-two healthy subjects were included. Vessel density before and during light stimulation was measured using optical coherence tomography angiography and assessed for the superficial, intermediate, and deep capillary plexus of the retinal circulation. Volumetric blood flow was measured using a custom-built Doppler optical coherence tomography system. Our results show that flicker stimulation induced a significant increase in the vessel density of +9.9 ± 6.7% in the superficial capillary plexus, +6.6 ± 1.7% in the intermediate capillary plexus, and +4.9 ± 2.3% in the deep capillary plexus. The hyperemic response of the superficial capillary plexus was significantly higher compared to the intermediate capillary plexus (P = 0.02) and deep capillary plexus (P = 0.002). Volumetric retinal blood flow increased by +39.9 ± 34.9% in arteries and by +29.8 ± 16.8% in veins. In conclusion, we showed a strong increase in the retinal microvascular density in response to light stimulation, with the most pronounced effect in the superficial capillary plexus. This is compatible with the hypothesis that the microvasculature exerts an important function in mediating functional hyperemia in humans.NEW & NOTEWORTHY We present vessel density alterations in response to flicker stimulation using optical coherence tomography angiography and identified the superficial capillary plexus as the layer with the most pronounced effect. This points out the physiological importance of the microvasculature in mediating functional hyperemia and suggests a fine-tuned plexus-specific mechanism to meet cellular metabolic demands.
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Affiliation(s)
- Martin Kallab
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Nikolaus Hommer
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Bingyao Tan
- Singapore Eye Research Institute, Singapore.,Institute of Health Technology, Nanyang Technological University, Singapore
| | - Martin Pfister
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.,Christian Doppler Laboratory for Ocular and Dermal Effects of Thiomers, Medical University of Vienna, Vienna, Austria.,Institute of Applied Physics, Vienna University of Technology, Vienna, Austria
| | - Andreas Schlatter
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.,Department of Ophthalmology, Vienna Institute for Research in Ocular Surgery-Karl Landsteiner Institute, Hanusch Hospital, Vienna, Austria
| | - René M Werkmeister
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Jacqueline Chua
- Singapore Eye Research Institute, Singapore.,Academic Clinical Program, Duke-NUS Medical School, Singapore
| | - Doreen Schmidl
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Leopold Schmetterer
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.,Singapore Eye Research Institute, Singapore.,Institute of Health Technology, Nanyang Technological University, Singapore.,Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.,Ophthalmology and Visual Sciences Academic Clinical Program, Duke-NUS Medical School, Singapore.,Institute of Clinical and Experimental Ophthalmology, Basel, Switzerland
| | - Gerhard Garhöfer
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
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12
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Full-field flicker evoked changes in parafoveal retinal blood flow. Sci Rep 2020; 10:16051. [PMID: 32994535 PMCID: PMC7524838 DOI: 10.1038/s41598-020-73032-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 09/08/2020] [Indexed: 12/16/2022] Open
Abstract
When retinal activity is increased by exposure to dynamic visual stimuli, blood vessels dilate and the flow of blood within vessels increases to meet the oxygen and glucose demands of the neurons. This relationship is termed ‘neurovascular coupling’ and it is critical for regulating control of the human retinal vasculature. In this study, we used a recently developed technique based on a dual-beam adaptive optics scanning laser ophthalmoscope to measure changes in red blood cell velocities, vessel diameter, and flow in interconnected small parafoveal retinal vessels (< 50 µm) of nine healthy participants. A full-field flicker stimulus was presented onto the retina to induce a vascular response to neural activity. Flicker stimulation increased blood velocity, vessel diameter, and therefore flow in arterioles, capillaries, and venules in all nine subjects. ANOVA and post hoc t-test showed significant increases in velocity and flow in arterioles and venules. These measurements indicate that the mechanism of neurovascular coupling systematically affects the vascular response in small retinal vessels in order to maintain hemodynamic regulation in the retina when exposed to visual stimulation, in our case flicker. Our findings may provide insight into future investigations on the impairments of neurovascular coupling from vascular diseases such as diabetic mellitus.
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Pappelis K, Choritz L, Jansonius NM. Microcirculatory model predicts blood flow and autoregulation range in the human retina: in vivo investigation with laser speckle flowgraphy. Am J Physiol Heart Circ Physiol 2020; 319:H1253-H1273. [PMID: 32986964 DOI: 10.1152/ajpheart.00404.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
In this study, we mathematically predict retinal vascular resistance (RVR) and retinal blood flow (RBF), we test predictions using laser speckle flowgraphy (LSFG), we estimate the range of vascular autoregulation, and we examine the relationship of RBF with the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC). Fundus, optical coherence tomography (OCT), and OCT-angiography images, systolic/diastolic blood pressure (SBP/DBP), and intraocular pressure (IOP) measurements were obtained from 36 human subjects. We modeled two circulation markers (RVR and RBF) and estimated individualized lower/higher autoregulation limits (LARL/HARL), using retinal vessel calibers, fractal dimension, perfusion pressure, and population-based hematocrit values. Quantitative LSFG waveforms were extracted from vessels of the same eyes, before and during IOP elevation. LSFG metrics explained most variance in RVR (R2 = 0.77/P = 6.9·10-9) and RBF (R2 = 0.65/P = 1.0·10-6), suggesting that the markers strongly reflect blood flow physiology. Higher RBF was associated with thicker RNFL (P = 4.0·10-4) and GCC (P = 0.003), thus also verifying agreement with structural measurements. LARL was at SBP/DBP of 105/65 mmHg for the average subject without arterial hypertension and at 115/75 mmHg for the average hypertensive subject. Moreover, during IOP elevation, changes in RBF were more pronounced than changes in RVR. These observations physiologically imply that healthy subjects are already close to LARL, thus prone to hypoperfusion. In conclusion, we modeled two clinical markers and described a novel method to predict individualized autoregulation limits. These findings could improve understanding of retinal perfusion and pave the way for personalized intervention decisions, when treating patients with coexisting ophthalmic and cardiovascular pathologies.NEW & NOTEWORTHY We describe and test a new approach to quantify retinal blood flow, based on standard clinical examinations and imaging techniques, linked together with a physiological model. We use these findings to generate individualized estimates of the autoregulation range. We provide evidence that healthy subjects are closer to the lower autoregulation limit than thought before. This suggests that some retinas are less prepared to withstand hypoperfusion, even after small intraocular pressure rises or blood pressure drops.
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Affiliation(s)
- Konstantinos Pappelis
- Department of Ophthalmology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.,Research School of Behavioural and Cognitive Neurosciences, Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands
| | - Lars Choritz
- University Eye Clinic, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Nomdo M Jansonius
- Department of Ophthalmology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.,Research School of Behavioural and Cognitive Neurosciences, Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands
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Gerhard G, Chua J, Tan B, Wong D, Schmidl D, Schmetterer L. Retinal Neurovascular Coupling in Diabetes. J Clin Med 2020; 9:jcm9092829. [PMID: 32882896 PMCID: PMC7565465 DOI: 10.3390/jcm9092829] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Revised: 08/23/2020] [Accepted: 08/27/2020] [Indexed: 12/15/2022] Open
Abstract
Neurovascular coupling, also termed functional hyperemia, is one of the physiological key mechanisms to adjust blood flow in a neural tissue in response to functional activity. In the retina, increased neural activity, such as that induced by visual stimulation, leads to the dilatation of retinal arterioles, which is accompanied by an immediate increase in retinal and optic nerve head blood flow. According to the current scientific view, functional hyperemia ensures the adequate supply of nutrients and metabolites in response to the increased metabolic demand of the neural tissue. Although the molecular mechanisms behind neurovascular coupling are not yet fully elucidated, there is compelling evidence that this regulation is impaired in a wide variety of neurodegenerative and vascular diseases. In particular, it has been shown that the breakdown of the functional hyperemic response is an early event in patients with diabetes. There is compelling evidence that alterations in neurovascular coupling precede visible signs of diabetic retinopathy. Based on these observations, it has been hypothesized that a breakdown of functional hyperemia may contribute to the retinal complications of diabetes such as diabetic retinopathy or macular edema. The present review summarizes the current evidence of impaired neurovascular coupling in patients with diabetes. In this context, the molecular mechanisms of functional hyperemia in health and disease will be covered. Finally, we will also discuss how neurovascular coupling may in future be used to monitor disease progression or risk stratification.
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Affiliation(s)
- Garhöfer Gerhard
- Department of Clinical Pharmacology, Medical University Vienna, 1090 Vienna, Austria; (G.G.); (D.S.)
| | - Jacqueline Chua
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 169856, Singapore; (J.C.); (B.T.); (D.W.)
- Academic Clinical Program, Duke-NUS Medical School, Singapore 169857, Singapore
- SERI-NTU Advanced Ocular Engineering (STANCE), Singapore 639798, Singapore
| | - Bingyao Tan
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 169856, Singapore; (J.C.); (B.T.); (D.W.)
- SERI-NTU Advanced Ocular Engineering (STANCE), Singapore 639798, Singapore
| | - Damon Wong
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 169856, Singapore; (J.C.); (B.T.); (D.W.)
- SERI-NTU Advanced Ocular Engineering (STANCE), Singapore 639798, Singapore
| | - Doreen Schmidl
- Department of Clinical Pharmacology, Medical University Vienna, 1090 Vienna, Austria; (G.G.); (D.S.)
| | - Leopold Schmetterer
- Department of Clinical Pharmacology, Medical University Vienna, 1090 Vienna, Austria; (G.G.); (D.S.)
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 169856, Singapore; (J.C.); (B.T.); (D.W.)
- Academic Clinical Program, Duke-NUS Medical School, Singapore 169857, Singapore
- SERI-NTU Advanced Ocular Engineering (STANCE), Singapore 639798, Singapore
- Institute for Health Technologies, Nanyang Technological University, Singapore 308232, Singapore
- Center for Medical Physics and Biomedical Engineering, Medical University Vienna, 1090 Vienna, Austria
- Institute of Molecular and Clinical Ophthalmology, CH-4031 Basel, Switzerland
- Correspondence: ; Tel.: +43-1-40400-29810
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Evaluation of flicker induced hyperemia in the retina and optic nerve head measured by Laser Speckle Flowgraphy. PLoS One 2018; 13:e0207525. [PMID: 30485331 PMCID: PMC6261588 DOI: 10.1371/journal.pone.0207525] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Accepted: 11/01/2018] [Indexed: 11/19/2022] Open
Abstract
Purpose The coupling between neural activity and blood flow is a physiological key principle of ocular blood flow regulation. The current study was performed to investigate whether Laser speckle flowgraphy (LSFG), a commercially available technique for measuring blood flow, is capable to assess flicker-induced haemodynamic changes in the retinal and optic nerve head (ONH) circulation. Methods Twenty healthy subjects were included in this cross sectional study. A commercial LSFG instrument was used to measure blood flow at the ONH as well as in retinal vessels before and during stimulation with flickering light. Mean blur rate (MBR), a measure of relative blood flow velocity, was obtained for the ONH and relative flow volume (RFV) a measure of relative blood flow of the respective retinal vessels. Results Stimulation with flicker light increased ONH MBR by +17.5%±6.6% (p<0.01). In retinal arteries, flicker stimulation led an increase of +23.8±10.0% (p<0.05) in total RFV. For retinal veins, an increase of +23.1%±11.0 (p<0.05) in total RFV was observed during stimulation. A higher response was observed in nasal RFV compared to temporal RFV in retinal arteries (nasal: +28.9%±20.0%; temporal: +20.4%±17.6%, p<0.05) and veins (nasal: +28.3%±19.6%; temporal +17.8%±18.9%, p<0.05). Conclusion As shown previously with other techniques, flicker stimulation leads to an increase in retinal and optic nerve head blood flow. Our results indicate that LSFG is an appropriate method for the quantification of retinal and ONH blood flow during visual stimulation and may be used as a non-invasive, easy to use tool to assess neuro-vascular coupling in humans.
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Albanna W, Kotliar K, Lüke JN, Alpdogan S, Conzen C, Lindauer U, Clusmann H, Hescheler J, Vilser W, Schneider T, Schubert GA. Non-invasive evaluation of neurovascular coupling in the murine retina by dynamic retinal vessel analysis. PLoS One 2018; 13:e0204689. [PMID: 30286110 PMCID: PMC6171857 DOI: 10.1371/journal.pone.0204689] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2018] [Accepted: 09/11/2018] [Indexed: 11/22/2022] Open
Abstract
Background Impairment of neurovascular coupling (NVC) was recently reported in the context of subarachnoid hemorrhage and may correlate with disease severity and outcome. However, previous techniques to evaluate NVC required invasive procedures. Retinal vessels may represent an alternative option for non-invasive assessment of NVC. Methods A prototype of an adapted retinal vessel analyzer was used to assess retinal vessel diameter in mice. Dynamic vessel analysis (DVA) included an application of monochromatic flicker light impulses in predefined frequencies for evaluating NVC. All retinae were harvested after DVA and electroretinograms were performed. Results A total of 104 retinal scans were conducted in 21 male mice (90 scans). Quantitative arterial recordings were feasible only in a minority of animals, showing an emphasized reaction to flicker light impulses (8 mice; 14 scans). A characteristic venous response to flicker light, however, could observed in the majority of animals. Repeated measurements resulted in a significant decrease of baseline venous diameter (7 mice; 7 scans, p < 0.05). Ex-vivo electroretinograms, performed after in-vivo DVA, demonstrated a significant reduction of transretinal signaling in animals with repeated DVA (n = 6, p < 0.001). Conclusions To the best of our knowledge, this is the first non-invasive study assessing murine retinal vessel response to flicker light with characteristic changes in NVC. The imaging system can be used for basic research and enables the investigation of retinal vessel dimension and function in control mice and genetically modified animals.
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Affiliation(s)
- Walid Albanna
- Institute for Neurophysiology, University of Cologne, Cologne, Germany
- Department of Neurosurgery, RWTH Aachen University, Aachen, Germany
- * E-mail:
| | - Konstantin Kotliar
- Department of Medical Engineering and Technomathematics, FH Aachen University of Applied Sciences, Aachen, Germany
| | - Jan Niklas Lüke
- Institute for Neurophysiology, University of Cologne, Cologne, Germany
| | - Serdar Alpdogan
- Institute for Neurophysiology, University of Cologne, Cologne, Germany
| | - Catharina Conzen
- Department of Neurosurgery, RWTH Aachen University, Aachen, Germany
| | - Ute Lindauer
- Department of Neurosurgery, RWTH Aachen University, Aachen, Germany
- Tranlational Neurosurgery and Neurobiology, RWTH Aachen University, Aachen, Germany
| | - Hans Clusmann
- Department of Neurosurgery, RWTH Aachen University, Aachen, Germany
| | - Jürgen Hescheler
- Institute for Neurophysiology, University of Cologne, Cologne, Germany
| | | | - Toni Schneider
- Institute for Neurophysiology, University of Cologne, Cologne, Germany
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Zhu Z, He C, Zhang Y, Yue X, Ba D. Mathematical method for analysis of the asymmetric retinal vascular networks. Eur J Ophthalmol 2018; 29:538-546. [PMID: 30270647 DOI: 10.1177/1120672118802952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE The purpose of this study was to quantitatively investigate the haemodynamics and oxygen transmission of the retina. METHODS Considering the effect of Fåhraeus-Lindqvist effect on the apparent viscosity of blood and the actual haematocrit in blood vessels, this study used the currently known retinal parameters (e.g. blood flow obtained by Doppler Fourier domain optical coherence tomography, FD-OCT for short) to construct a retinal blood circulation model consisting of an asymmetric vascular network system. RESULTS The blood flow velocity and the vascular diameter in the retinal blood vessels satisfied the exponential relationship. The wall shear stress was related to the release of nitric oxide synthase and endothelin-1 by endothelial cells and played an important role in retinal blood flow regulation. In the retinal arteries, the oxygen tension ranged from 98 to 65 mmHg, and the oxygen saturation ranged from 97.3% to 92.2%. In the retinal veins, the oxygen tension was approximately 41.8 mmHg, and the oxygen saturation ranged from 79.2% to 77.3%. The difference in oxygen content of the arteriovenous network was 5.4 (ml O2/dl blood), and the oxygen extraction of the superior temporal arteriovenous network was 86 (μl/min*ml O2/dl blood). CONCLUSION Compared with previous relevant experimental data, the numerical model established in this article demonstrates reliability. It also helps advance our understanding of the retinal pathological processes related to hemodynamics and metabolism.
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Affiliation(s)
- Zhipeng Zhu
- School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China
| | - Chao He
- School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China
| | - Yingli Zhang
- School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China
| | - Xiangji Yue
- School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China
| | - Dechun Ba
- School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China
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Colligris P, Perez de Lara MJ, Colligris B, Pintor J. Ocular Manifestations of Alzheimer's and Other Neurodegenerative Diseases: The Prospect of the Eye as a Tool for the Early Diagnosis of Alzheimer's Disease. J Ophthalmol 2018; 2018:8538573. [PMID: 30151279 PMCID: PMC6091327 DOI: 10.1155/2018/8538573] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Revised: 06/07/2018] [Accepted: 06/26/2018] [Indexed: 12/20/2022] Open
Abstract
Dementia, including Alzheimer's disease (AD), is a major disorder, leading to several ocular manifestations amongst the elderly population. These visual disorders may be due to retinal nerve degenerative changes, including nerve fibre layer thinning, degeneration of retinal ganglion cells, and changes to vascular parameters. There is no cure for Alzheimer's, but medicines can slow down the development of many of the classic symptoms, such as loss of memory and communication skills, mood swings, and depression. The disease diagnosis is difficult, and it is only possible through PET scans of the brain, detecting evidence of the accumulation of amyloid and tau. PET is expensive and invasive, requiring the injection of radioactive tracers, which bind with these proteins and glow during scanning. Recently, scientists developed promising eye-scan techniques that may detect Alzheimer's disease at its earliest stage, before major symptoms appear, leading to improved management of the disease symptoms. In this review, we are discussing the visual abnormalities of Alzheimer's and other neurodegenerative diseases, focused on ocular functional-visual-structural biomarkers, retinal pathology, and potential novel diagnostic tools.
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Affiliation(s)
- Pade Colligris
- Universidad Alfonso X, Madrid, Spain
- Ocupharm Diagnostics SL, Madrid, Spain
| | | | - Basilio Colligris
- Ocupharm Diagnostics SL, Madrid, Spain
- Universidad Complutense de Madrid, Madrid, Spain
| | - Jesus Pintor
- Ocupharm Diagnostics SL, Madrid, Spain
- Universidad Complutense de Madrid, Madrid, Spain
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