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Raghavendra AJ, Damani A, Oechsli S, Magder LS, Liu Z, Hammer DX, Saeedi OJ. Measurement of retinal blood flow precision in the human eye with multimodal adaptive optics imaging. BIOMEDICAL OPTICS EXPRESS 2024; 15:4625-4641. [PMID: 39346998 PMCID: PMC11427214 DOI: 10.1364/boe.524944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2024] [Revised: 06/08/2024] [Accepted: 06/30/2024] [Indexed: 10/01/2024]
Abstract
Impaired retinal blood flow (RBF) autoregulation plays a key role in the development and progression of several ocular diseases, including glaucoma and diabetic retinopathy. Clinically, reproducible RBF quantitation could significantly improve early diagnosis and disease management. Several non-invasive techniques have been developed but are limited for retinal microvasculature flow measurements due to their low signal-to-noise ratio and poor lateral resolution. In this study, we demonstrate reproducible vessel caliber and retinal blood flow velocity measurements in healthy human volunteers using a high-resolution (spatial and temporal) multimodal adaptive optics system with scanning laser ophthalmoscopy and optical coherence tomography.
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Affiliation(s)
- Achyut J Raghavendra
- Department of Ophthalmology and Visual Sciences, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
- Center for Devices and Radiological Health (CDRH), U. S. Food and Drug Administration (FDA), Silver Spring, Maryland 20993, USA
| | - Aashka Damani
- Department of Ophthalmology and Visual Sciences, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Saige Oechsli
- Department of Ophthalmology and Visual Sciences, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Laurence S Magder
- Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Zhuolin Liu
- Center for Devices and Radiological Health (CDRH), U. S. Food and Drug Administration (FDA), Silver Spring, Maryland 20993, USA
| | - Daniel X Hammer
- Center for Devices and Radiological Health (CDRH), U. S. Food and Drug Administration (FDA), Silver Spring, Maryland 20993, USA
| | - Osamah J Saeedi
- Department of Ophthalmology and Visual Sciences, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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2
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Neriyanuri S, Bedggood P, Symons RCA, Metha AB. Validation of an automated method for studying retinal capillary blood flow. BIOMEDICAL OPTICS EXPRESS 2024; 15:802-817. [PMID: 38404315 PMCID: PMC10890846 DOI: 10.1364/boe.504074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Revised: 12/13/2023] [Accepted: 12/28/2023] [Indexed: 02/27/2024]
Abstract
Two major approaches for tracking cellular motion across a range of biological tissues are the manual labelling of cells, and automated analysis of spatiotemporal information represented in a kymograph. Here we compare these two approaches for the measurement of retinal capillary flow, a particularly noisy application due to the low intrinsic contrast of single red blood cells (erythrocytes). Image data were obtained using a flood-illuminated adaptive optics ophthalmoscope at 750 nm, allowing the acquisition of flow information over several cardiac cycles which provided key information in evaluating tracking accuracy. Our results show that in addition to being much faster, the automated method is more accurate in the face of rapid flow and reduced image contrast. This study represents the first validation of commonly used kymograph approaches to capillary flow analysis.
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Affiliation(s)
- Srividya Neriyanuri
- Department of Optometry and Vision Sciences, The University of Melbourne, VIC 3053, Australia
| | - Phillip Bedggood
- Department of Optometry and Vision Sciences, The University of Melbourne, VIC 3053, Australia
| | - R. C. Andrew Symons
- Department of Optometry and Vision Sciences, The University of Melbourne, VIC 3053, Australia
- Department of Surgery, The University of Melbourne, VIC 3053, Australia
- Centre for Eye Research (CERA), VIC 3002, Australia
- Department of Surgery, Alfred Hospital, Monash University, VIC 3004, Australia
| | - Andrew B. Metha
- Department of Optometry and Vision Sciences, The University of Melbourne, VIC 3053, Australia
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Neriyanuri S, Bedggood P, Symons RCA, Metha A. Mapping the human parafoveal vascular network to understand flow variability in capillaries. PLoS One 2023; 18:e0292962. [PMID: 37831712 PMCID: PMC10575526 DOI: 10.1371/journal.pone.0292962] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2023] [Accepted: 10/03/2023] [Indexed: 10/15/2023] Open
Abstract
Capillary flow is known to be non-homogenous between vessels and variable over time, for reasons that are poorly understood. The local properties of individual vessels have been shown to have limited explanatory power in this regard. This exploratory study investigates the association of network-level properties such as vessel depth, branch order, and distance from the feeding arteriole with capillary flow. Detailed network connectivity analysis was undertaken in 3 healthy young subjects using flood-illuminated adaptive optics retinal imaging, with axial depth of vessels determined via optical coherence tomography angiography. Forty-one out of 70 vessels studied were of terminal capillary type, i.e. fed from an arterial junction and drained by a venous junction. Approximately half of vessel junctions were amenable to fitting with a model of relative branch diameters, with only a few adhering to Murray's Law. A key parameter of the model (the junction exponent) was found to be inversely related to the average velocity (r = -0.59, p = 0.015) and trough velocity (r = -0.67, p = 0.004) in downstream vessels. Aspects of cellular flow, such as the minimum velocity, were also moderately correlated (r = 0.46, p = 0.009) with distance to the upstream feeding arteriole. Overall, this study shows that capillary network topology contributes significantly to the flow variability in retinal capillaries in human eyes. Understanding the heterogeneity in capillary flow is an important first step before pathological flow states can be properly understood. These results show that flow within capillary vessels is not affected by vessel depths but significantly influenced by the upstream feeder distance as well as the downstream vessel junction exponents, but there remains much to be uncovered regarding healthy capillary flow.
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Affiliation(s)
- Srividya Neriyanuri
- Department of Optometry and Vision Sciences, The University of Melbourne, Victoria, Australia
| | - Phillip Bedggood
- Department of Optometry and Vision Sciences, The University of Melbourne, Victoria, Australia
| | - R. C. Andrew Symons
- Department of Optometry and Vision Sciences, The University of Melbourne, Victoria, Australia
- Department of Surgery, The University of Melbourne, Victoria, Australia
- Centre for Eye Research Australia, Victoria, Australia
- Department of Surgery, Alfred Hospital, Monash University, Victoria, Australia
| | - Andrew Metha
- Department of Optometry and Vision Sciences, The University of Melbourne, Victoria, Australia
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Tsai J, Asanad S, Whiting M, Zhang X, Magder L, Saeedi O. Repeatability and Comparability of Retinal Blood Vessel Caliber Measurements by OCTA. Vision (Basel) 2023; 7:48. [PMID: 37489327 PMCID: PMC10366731 DOI: 10.3390/vision7030048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Revised: 05/23/2023] [Accepted: 06/16/2023] [Indexed: 07/26/2023] Open
Abstract
BACKGROUND To investigate the repeatability in vessel caliber measurements by optical coherence tomography angiography (OCTA). METHODS In this prospective study, 28 patients (47 eyes) underwent sequential OCTA imaging of the optic nerve head and macula. Two independent masked graders measured vessel caliber for sequential images of the optic nerve head and macula. The average vessel width was determined and variability between graders and images. RESULTS A total of 8400 measurements of 420 vessels from 84 OCTA images were included in the analysis. Overall, inter-grader agreement was excellent (ICC 0.90). The coefficient of variation (CoV) for all repeated OCTA images was 0.10. Greater glaucoma severity, older age, macular location, and diagnosis of diabetes were associated with thinner vessels (p < 0.05). CoV was higher in the peripapillary region (0.07) as compared to the macula (0.15). ICC was high for all subgroups except for the macula (ICC = 0.72). CONCLUSIONS Overall, the repeatability of vessel caliber measurements by OCTA was high and variability low. There was greater variability in the measurement of macular vessels, possibly due to technical limitations in acquiring accurate vessel widths for smaller macular vessels.
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Affiliation(s)
- Joby Tsai
- Department of Ophthalmology, Broward Health, Deerfield Beach, FL 33064, USA
| | - Samuel Asanad
- Department of Ophthalmology and Visual Sciences, University of Maryland, Baltimore, MD 21201, USA
| | - Martha Whiting
- Department of Ophthalmology and Visual Sciences, University of Maryland, Baltimore, MD 21201, USA
| | - Xuemin Zhang
- Department of Ophthalmology and Visual Sciences, University of Maryland, Baltimore, MD 21201, USA
| | - Laurence Magder
- Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Osamah Saeedi
- Department of Ophthalmology and Visual Sciences, University of Maryland, Baltimore, MD 21201, USA
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Neriyanuri S, Bedggood P, Symons RCA, Metha AB. Flow Heterogeneity and Factors Contributing to the Variability in Retinal Capillary Blood Flow. Invest Ophthalmol Vis Sci 2023; 64:15. [PMID: 37450310 DOI: 10.1167/iovs.64.10.15] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/18/2023] Open
Abstract
Purpose Capillary flow plays an important role in the nourishment and maintenance of healthy neural tissue and can be observed directly and non-invasively in the living human retina. Despite their importance, patterns of normal capillary flow are not well understood due to limitations in spatial and temporal resolution of imaging data. Methods Capillary flow characteristics were studied in the retina of three healthy young individuals using a high-resolution adaptive optics ophthalmoscope. Imaging with frame rates of 200 to 300 frames per second was sufficient to capture details of the single-file flow of red blood cells in capillaries over the course of about 3 seconds. Results Erythrocyte velocities were measured from 72 neighboring vessels of the parafoveal capillary network for each subject. We observed strong variability among vessels within a given subject, and even within a given imaged field, across a range of capillary flow parameters including maximum and minimum velocities, pulsatility, abruptness of the systolic peak, and phase of the cardiac cycle. The observed variability was not well explained by "local" factors such as the vessel diameter, tortuosity, length, linear cell density, or hematocrit of the vessel. Within a vessel, a moderate relation between the velocities and hematocrit was noted, suggesting a redistribution of plasma between cells with changes in flow. Conclusions These observations advance our fundamental understanding of normal capillary physiology and raise questions regarding the potential role of network-level effects in explaining the observed flow heterogeneity.
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Affiliation(s)
- Srividya Neriyanuri
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
| | - Phillip Bedggood
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
| | - R C Andrew Symons
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
- Department of Surgery, The University of Melbourne, Parkville, Victoria, Australia
- Centre for Eye Research Australia, East Melbourne, Victoria, Australia
- Department of Surgery, Alfred Hospital, Monash University, Melbourne, Victoria, Australia
| | - Andrew B Metha
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
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Williams DR, Burns SA, Miller DT, Roorda A. Evolution of adaptive optics retinal imaging [Invited]. BIOMEDICAL OPTICS EXPRESS 2023; 14:1307-1338. [PMID: 36950228 PMCID: PMC10026580 DOI: 10.1364/boe.485371] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 02/02/2023] [Indexed: 05/02/2023]
Abstract
This review describes the progress that has been achieved since adaptive optics (AO) was incorporated into the ophthalmoscope a quarter of a century ago, transforming our ability to image the retina at a cellular spatial scale inside the living eye. The review starts with a comprehensive tabulation of AO papers in the field and then describes the technological advances that have occurred, notably through combining AO with other imaging modalities including confocal, fluorescence, phase contrast, and optical coherence tomography. These advances have made possible many scientific discoveries from the first maps of the topography of the trichromatic cone mosaic to exquisitely sensitive measures of optical and structural changes in photoreceptors in response to light. The future evolution of this technology is poised to offer an increasing array of tools to measure and monitor in vivo retinal structure and function with improved resolution and control.
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Affiliation(s)
- David R. Williams
- The Institute of Optics and the Center for
Visual Science, University of Rochester,
Rochester NY, USA
| | - Stephen A. Burns
- School of Optometry, Indiana
University at Bloomington, Bloomington IN, USA
| | - Donald T. Miller
- School of Optometry, Indiana
University at Bloomington, Bloomington IN, USA
| | - Austin Roorda
- Herbert Wertheim School of Optometry and
Vision Science, University of California at Berkeley, Berkeley CA, USA
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Düzgün E, Şahin T, Yeşiltaş SK, Alkan AA, Dikmen NT. Ozone-induced retinal vascular reactivity as assessed by optical coherence tomography angiography. Photodiagnosis Photodyn Ther 2022; 39:102957. [PMID: 35690324 DOI: 10.1016/j.pdpdt.2022.102957] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2022] [Revised: 05/18/2022] [Accepted: 06/07/2022] [Indexed: 11/26/2022]
Abstract
BACKGROUND This study aimed to investigate the retinal vascular reactivity (RVR) of the macular and peripapillary capillary network in response to ozonated autohemotherapy (AHT) using optical coherence tomography angiography (OCTA). METHODS This was a single-centre prospective study. All participants that were planned to have a combination of major and minor ozone AHT underwent a complete ocular examination and OCTA imaging before and after the ozone AHT. Foveal avascular zone (FAZ) metrics and vessel density (VD) of superficial (SCP), deep capillary plexus (DCP), and radial peripapillary capillary (RPC) plexus were assessed using the built-in software. RESULTS A total of 40 right eyes of 40 individuals were included. No significant differences were observed for the mean values of the FAZ metrics and choriocapillaris flow area following ozone AHT compared with baseline values (p > 0.05). The mean whole VD of SCP and DCP was 47.80 ± 2.18% and 53.09 ± 3.00% before treatment, which decreased to 47.68 ± 2.7% and 52.38 ± 3.07% after treatment (p = 0.660 and p = 0.097, respectively). No significant differences were observed in the vascular densities of both SCP and DCP in any quadrant (p > 0.05). The RPC density did not show significant alterations compared with baseline values, except the inferior-hemi region. The VD in the inferior-hemi peripapillary quadrant was significantly increased after ozone AHT (p = 0.034). CONCLUSION The ozone AHT did not cause evident RVR in the macular area, whereas the peripapillary area showed a partial response.
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Affiliation(s)
- Eyüp Düzgün
- Department of Ophthalmology, Sisli Hamidiye Etfal Training and Research Hospital, University of Health Sciences, Istanbul, Turkey.
| | - Tülay Şahin
- Department of Physical Therapy and Rehabilitation, Sisli Hamidiye Etfal Training and Research Hospital, University of Health Sciences, Istanbul, Turkey
| | - Sümeyra Keleş Yeşiltaş
- Department of Ophthalmology, Sisli Hamidiye Etfal Training and Research Hospital, University of Health Sciences, Istanbul, Turkey
| | - Abdurrahman Alpaslan Alkan
- Department of Ophthalmology, Sisli Hamidiye Etfal Training and Research Hospital, University of Health Sciences, Istanbul, Turkey
| | - Nejla Tükenmez Dikmen
- Department of Ophthalmology, Sultan Abdulhamid Han Training and Research Hospital, University of Health Sciences, Istanbul, Turkey
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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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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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10
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Abstract
Advances in retinal imaging are enabling researchers and clinicians to make precise noninvasive measurements of the retinal vasculature in vivo. This includes measurements of capillary blood flow, the regulation of blood flow, and the delivery of oxygen, as well as mapping of perfused blood vessels. These advances promise to revolutionize our understanding of vascular regulation, as well as the management of retinal vascular diseases. This review provides an overview of imaging and optical measurements of the function and structure of the ocular vasculature. We include general characteristics of vascular systems with an emphasis on the eye and its unique status. The functions of vascular systems are discussed, along with physical principles governing flow and its regulation. Vascular measurement techniques based on reflectance and absorption are briefly introduced, emphasizing ways of generating contrast. One of the prime ways to enhance contrast within vessels is to use techniques sensitive to the motion of cells, allowing precise measurements of perfusion and blood velocity. Finally, we provide a brief introduction to retinal vascular diseases.
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Affiliation(s)
- Stephen A Burns
- Indiana University School of Optometry, Bloomington, Indiana 47405, USA; , ,
| | - Ann E Elsner
- Indiana University School of Optometry, Bloomington, Indiana 47405, USA; , ,
| | - Thomas J Gast
- Indiana University School of Optometry, Bloomington, Indiana 47405, USA; , ,
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11
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Abdolahi F, Zhou X, Ashimatey BS, Chu Z, Jiang X, Wang RK, Kashani AH. Optical Coherence Tomography Angiography-Derived Flux As a Measure of Physiological Changes in Retinal Capillary Blood Flow. Transl Vis Sci Technol 2021; 10:5. [PMID: 34342607 PMCID: PMC8340668 DOI: 10.1167/tvst.10.9.5] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Purpose To compare optical coherence tomography angiography (OCTA)–derived flux with conventional OCTA measures of retinal vascular density in assessment of physiological changes in retinal blood flow. Methods Healthy subjects were recruited, and 3 × 3-mm2 fovea-centered scans were acquired using commercially available swept-source OCTA (SS-OCTA) while participants were breathing room air, 100% O2, or 5% CO2. Retinal perfusion was quantified using vessel area density (VAD) and vessel skeleton density (VSD), as well as novel measures of retinal perfusion, vessel area flux (VAF) and vessel skeleton flux (VSF). Flux is proportional to the number of red blood cells moving through a vessel segment per unit time. The percentage change in each measure was compared between the O2 and CO2 gas conditions for images of all vessels (arterioles, venules, and capillaries) and capillary-only images. Statistical significance was determined using paired t-tests and a linear mixed-effects model. Results Eighty-four OCTA scans from 29 subjects were included (age, 45.9 ± 19.5 years; 14 male, 48.3%). In capillary-only images, the change under the CO2 condition was 168% greater in VAF than in VAD (P = 0.002) and 124% greater in VSF than in VSD (P = 0.004). Similarly, under the O2 condition, the change was 94% greater in VAF than in VAD (P = 0.004) and 57% greater in VSF than in VSD (P = 0.01). Flux measures showed significantly greater change in capillary-only images compared with all-vessels images. Conclusions OCTA-derived flux measures quantify physiological changes in retinal blood flow at the capillary level with a greater effect size than conventional vessel density measures. Translational Relevance OCTA-derived flux is a useful measure of subclinical changes in retinal capillary perfusion.
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Affiliation(s)
- Farzan Abdolahi
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, CA, USA
| | - Xiao Zhou
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Bright S Ashimatey
- Wilmer Eye Institute, Johns Hopkins School of Medicine, Baltimore, MD, USA
| | - Zhongdi Chu
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Xuejuan Jiang
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, CA, USA
| | - Ruikang K Wang
- Department of Bioengineering, University of Washington, Seattle, WA, USA.,Department of Ophthalmology, University of Washington Seattle, WA, USA
| | - Amir H Kashani
- Wilmer Eye Institute, Johns Hopkins School of Medicine, Baltimore, MD, USA
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12
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Past, present and future role of retinal imaging in neurodegenerative disease. Prog Retin Eye Res 2021; 83:100938. [PMID: 33460813 PMCID: PMC8280255 DOI: 10.1016/j.preteyeres.2020.100938] [Citation(s) in RCA: 62] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 12/11/2020] [Accepted: 12/17/2020] [Indexed: 02/08/2023]
Abstract
Retinal imaging technology is rapidly advancing and can provide ever-increasing amounts of information about the structure, function and molecular composition of retinal tissue in humans in vivo. Most importantly, this information can be obtained rapidly, non-invasively and in many cases using Food and Drug Administration-approved devices that are commercially available. Technologies such as optical coherence tomography have dramatically changed our understanding of retinal disease and in many cases have significantly improved their clinical management. Since the retina is an extension of the brain and shares a common embryological origin with the central nervous system, there has also been intense interest in leveraging the expanding armamentarium of retinal imaging technology to understand, diagnose and monitor neurological diseases. This is particularly appealing because of the high spatial resolution, relatively low-cost and wide availability of retinal imaging modalities such as fundus photography or OCT compared to brain imaging modalities such as magnetic resonance imaging or positron emission tomography. The purpose of this article is to review and synthesize current research about retinal imaging in neurodegenerative disease by providing examples from the literature and elaborating on limitations, challenges and future directions. We begin by providing a general background of the most relevant retinal imaging modalities to ensure that the reader has a foundation on which to understand the clinical studies that are subsequently discussed. We then review the application and results of retinal imaging methodologies to several prevalent neurodegenerative diseases where extensive work has been done including sporadic late onset Alzheimer's Disease, Parkinson's Disease and Huntington's Disease. We also discuss Autosomal Dominant Alzheimer's Disease and cerebrovascular small vessel disease, where the application of retinal imaging holds promise but data is currently scarce. Although cerebrovascular disease is not generally considered a neurodegenerative process, it is both a confounder and contributor to neurodegenerative disease processes that requires more attention. Finally, we discuss ongoing efforts to overcome the limitations in the field and unmet clinical and scientific needs.
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13
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Bedggood P, Metha A. Adaptive optics imaging of the retinal microvasculature. Clin Exp Optom 2021; 103:112-122. [DOI: 10.1111/cxo.12988] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 09/17/2019] [Accepted: 09/20/2019] [Indexed: 12/31/2022] Open
Affiliation(s)
- Phillip Bedggood
- Department of Optometry and Vision Sciences, The University of Melbourne, Melbourne, Australia,
| | - Andrew Metha
- Department of Optometry and Vision Sciences, The University of Melbourne, Melbourne, Australia,
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Akyol E, Hagag AM, Sivaprasad S, Lotery AJ. Adaptive optics: principles and applications in ophthalmology. Eye (Lond) 2021; 35:244-264. [PMID: 33257798 PMCID: PMC7852593 DOI: 10.1038/s41433-020-01286-z] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Revised: 10/19/2020] [Accepted: 11/04/2020] [Indexed: 12/26/2022] Open
Abstract
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.
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Affiliation(s)
- Engin Akyol
- Faculty of Medicine, University of Southampton, Southampton, SO17 1BJ, UK
| | - Ahmed M Hagag
- NIHR Moorfields Biomedical Research Centre, Moorfields Eye Hospital NHS Foundation Trust, London, EC1V 2PD, UK
- UCL Institute of Ophthalmology, London, EC1V 9EL, UK
| | - Sobha Sivaprasad
- NIHR Moorfields Biomedical Research Centre, Moorfields Eye Hospital NHS Foundation Trust, London, EC1V 2PD, UK
- UCL Institute of Ophthalmology, London, EC1V 9EL, UK
| | - Andrew J Lotery
- Faculty of Medicine, University of Southampton, Southampton, SO17 1BJ, UK.
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Singer M, Ashimatey BS, Zhou X, Chu Z, Wang R, Kashani AH. Impaired layer specific retinal vascular reactivity among diabetic subjects. PLoS One 2020; 15:e0233871. [PMID: 32915787 PMCID: PMC7485884 DOI: 10.1371/journal.pone.0233871] [Citation(s) in RCA: 8] [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: 05/12/2020] [Accepted: 08/29/2020] [Indexed: 01/04/2023] Open
Abstract
PURPOSE To investigate layer specific retinal vascular reactivity (RVR) in capillaries of diabetic subjects without DR or with only mild non-proliferative diabetic retinopathy (NPDR). METHODS A previously described nonrebreathing apparatus was used to deliver room air, 5% CO2, or 100% O2 to 41 controls and 22 diabetic subjects (with mild or no NPDR) while simultaneously acquiring fovea-centered 3x3mm2 Swept-Source Optical Coherence Tomography Angiography (SS-OCTA) images. Vessel skeleton density (VSD) and vessel diameter index (VDI) were calculated for each gas condition for the superficial retinal layer (SRL) and deep retinal layer (DRL). The superficial layer analysis excluded arterioles and venules. Data analysis was performed using mixed factorial analysis of covariance stratified by diabetic status. All models were adjusted for age, gender, and hypertension, and statistical significance for multiple comparisons from posthoc comparisons were defined at p<0.017. RESULTS Among controls, there was a significant difference in capillary VSD between all gas conditions (p<0.001). This difference was present in both the SRL and DRL. Among diabetics, there was no significant difference in response to CO2 conditions in the SRL (p = 0.072), and a blunted response to both CO2 (p = 0.9) and O2 in the DRL (p = 0.019). A significant gas effect was detected in the capillary VDI in the SRL of controls (p = 0.001), which was driven by higher VDI in the oxygen condition compared to that of carbon dioxide. CONCLUSIONS Impairment in RVR in diabetic subjects is characterized by a paradoxical response to CO2 in both the SRL and DRL as well as an attenuated response to O2 in the DRL. These layer and gas specific impairments in diabetics seem to occur early in the disease and to be driven primarily at the capillary level.
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Affiliation(s)
- Maxwell Singer
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States of America
| | - Bright S. Ashimatey
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States of America
| | - Xiao Zhou
- Department of Bioengineering, University of Washington, Seattle, Washington, United States of America
| | - Zhongdi Chu
- Department of Bioengineering, University of Washington, Seattle, Washington, United States of America
| | - Ruikang Wang
- Department of Bioengineering, University of Washington, Seattle, Washington, United States of America
- Department of Ophthalmology, University of Washington, Seattle, Washington, United States of America
| | - Amir H. Kashani
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States of America
- USC Ginsburg Institute for Biomedical Therapeutics, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States of America
- * E-mail: ,
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Bedggood P, Metha A. Recovering the appearance of the capillary blood column from under-sampled flow data. OPTICS LETTERS 2020; 45:4320-4323. [PMID: 32735288 DOI: 10.1364/ol.398168] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Accepted: 06/23/2020] [Indexed: 06/11/2023]
Abstract
The regular spacing of cells in capillary flow results in spurious cell trajectories if the sampling rate is too low. This makes it difficult to identify cells, even if the velocity is known. Here, we demonstrate a software method to overcome this problem and validate it using high frame rate data with known velocity, which is downsampled to produce aliasing. The method assumes high spatial sampling, constant velocity over short epochs, and an incompressible blood column. Data in successive frames are shifted along the capillary tube axis according to the flow velocity, faithfully rendering cells and plasma. The velocity estimate, required as input to this procedure, can be obtained from either a) the blind optimization of a simple heuristic, or b) a recently proposed velocimetry algorithm, which appears to extend the aliasing limit.
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Kushner-Lenhoff S, Ashimatey BS, Kashani AH. Retinal Vascular Reactivity as Assessed by Optical Coherence Tomography Angiography. J Vis Exp 2020. [PMID: 32281974 DOI: 10.3791/60948] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The vascular supply to the retina has been shown to dynamically adapt through vasoconstriction and vasodilation to accommodate the metabolic demands of the retina. This process, referred to as retinal vascular reactivity (RVR), is mediated by neurovascular coupling, which is impaired very early in retinal vascular diseases such as diabetic retinopathy. Therefore, a clinically feasible method of assessing vascular function may be of significant interest in both research and clinical settings. Recently, in vivo imaging of the retinal vasculature at the capillary level has been made possible by the FDA approval of optical coherence tomography angiography (OCTA), a noninvasive, minimal risk and dyeless angiography method with capillary level resolution. Concurrently, physiological and pathological changes in RVR have been shown by several investigators. The method shown in this manuscript is designed to investigate RVR using OCTA with no need for alterations to the clinical imaging procedures or device. It demonstrates real time imaging of the retina and retinal vasculature during exposure to hypercapnic or hyperoxic conditions. The exam is easily performed with two personnel in under 30 min with minimal subject discomfort or risk. This method is adaptable to other ophthalmic imaging devices and the applications may vary based on the composition of the gas mixture and patient population. A strength of this method is that it allows for an investigation of retinal vascular function at the capillary level in human subjects in vivo. Limitations of this method are largely those of OCTA and other retinal imaging methods including imaging artifacts and a restricted dynamic range. The results obtained from the method are OCT and OCTA images of the retina. These images are amenable to any analysis that is possible on commercially available OCT or OCTA devices. The general method, however, can be adapted to any form of ophthalmic imaging.
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Affiliation(s)
| | | | - Amir H Kashani
- Department of Ophthalmology, USC Roski Eye Institute; USC Ginsberg Institute for Biomedical Therapeutics, Keck School of Medicine of the University of Southern California;
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Hypercapnia Impairs Vasoreactivity to Changes in Blood Pressure and Intraocular Pressure in Rat Retina. Optom Vis Sci 2020; 96:470-476. [PMID: 31274734 DOI: 10.1097/opx.0000000000001400] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
SIGNIFICANCE The balance between oxygen and carbon dioxide sets the resting tone (or diameter) of retinal blood vessels. Eyes that are hypercapnic use up their "vasodilatory reserve" and therefore fail to respond adequately to changes in intraocular or blood pressure. PURPOSE Retinal vessels are regulated by both myogenic and metabolic mechanisms. We considered whether alteration of metabolic status would modify the vascular response to ocular perfusion pressure (OPP) lowering in rat retina. METHODS In pentobarbital anesthetized adult Brown-Norway rats, normocapnia or hypercapnia was achieved by artificially ventilating animals with air or 5% carbon dioxide in ~30% oxygen, respectively. Ocular perfusion pressure was gradually reduced to ~20 mmHg by either lowering blood pressure (slowly drawing blood from a femoral artery/vein) or manometrically increasing intraocular pressure under normocapnic or hypercapnic conditions. In all four groups (n = 7 eyes for each), a confocal scanning laser ophthalmoscope was used to acquire image sequences centered on the optic nerve throughout pressure modification. The diameter of arterioles and venules at various OPP levels was measured and expressed as percentage relative to their own baseline. The response of arterioles and venules to OPP lowering was compared between normocapnic and hypercapnic groups. RESULTS Average arterial carbon dioxide partial pressures were 36.9 ± 2.6 mmHg in normocapnic and 64.1 ± 5.9 mmHg in hypercapnic (P < .001) animals. In the normocapnic groups, blood pressure lowering and intraocular pressure elevation resulted in significant vasodilation of both arterioles and venules (P < .0001). In the hypercapnic groups, OPP lowering-induced vasodilation was significantly attenuated compared with the corresponding normocapnic groups (P < .0001 for both, two-way analysis of variance). CONCLUSION Hypercapnia significantly modified myogenic vascular autoregulation in response to OPP reduction.
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Ashimatey BS, Green KM, Chu Z, Wang RK, Kashani AH. Impaired Retinal Vascular Reactivity in Diabetic Retinopathy as Assessed by Optical Coherence Tomography Angiography. Invest Ophthalmol Vis Sci 2019; 60:2468-2473. [PMID: 31173077 PMCID: PMC6557617 DOI: 10.1167/iovs.18-26417] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Purpose To assess retinal vascular reactivity in healthy controls and subjects with diabetic retinopathy (DR). Methods A total of 22 healthy control eyes and 16 eyes with DR were enrolled. Images were acquired using a commercially available swept-source optical coherence tomography angiography (SS-OCTA) system. Three conditions were tested for each patient (hyperoxia, hypercapnia, and room-air) by employing a non-rebreathing apparatus that delivered appropriate gas mixtures (100% O2, 5% CO2, room air). Vessel skeleton density (VSD) and vessel diameter index (VDI) were compared between the conditions using mixed-model ANOVA adjusting for age and hypertension. Significant gas or interaction effects were followed by a Bonferroni adjusted pairwise post hoc analysis. Statistical significance was defined at P < 0.05. Results The mixed-model ANOVA of the VSD found a significant intraindividual gas effect (F[2, 70] = 20.3, P < 0.001) and intergroup effect (F[1, 35] = 6.9, P = 0.001), and interaction effects (F[2, 70] = 4.6, P = 0.03). The post hoc pairwise comparison found significant differences among all three gas conditions in the healthy controls. In the subjects with DR, there were significant differences in VSD between hyperoxic and room air, and between hyperoxic and hypercapnic conditions, but not between hypercapnic and room-air conditions. Similar results were found for VDI. Conclusions The retinal capillaries, assessed with SS-OCTA, in subjects with DR preferentially reacted to hyperoxia but not hypercapnia, while the healthy controls reacted to both. The difference in the vascular reactivity may be indicative of the underlying pathophysiology of DR.
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Affiliation(s)
- Bright S. Ashimatey
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States
| | - Kyle M. Green
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States
| | - Zhongdi Chu
- Department of Bioengineering, University of Washington, Seattle, Washington, United States
| | - Ruikang K. Wang
- Department of Bioengineering, University of Washington, Seattle, Washington, United States
,Department of Ophthalmology, University of Washington, Seattle, Washington, United States
| | - Amir H. Kashani
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States
,USC Ginsberg Institute for Biomedical Therapeutics, Los Angeles, California, United States
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Mecê P, Gofas-Salas E, Petit C, Cassaing F, Sahel J, Paques M, Grieve K, Meimon S. Higher adaptive optics loop rate enhances axial resolution in nonconfocal ophthalmoscopes. OPTICS LETTERS 2019; 44:2208-2211. [PMID: 31042185 DOI: 10.1364/ol.44.002208] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
In this Letter, we propose a way to better understand the impact of dynamic ocular aberrations in the axial resolution of nonconfocal adaptive optics (AO) ophthalmoscopes via a simulation of the 3D PSF in the retina for various AO-loop rates. We then use optical incoherence tomography, a method enabling the generation of tomographic retinal cross sections in incoherent imaging systems, to evaluate the benefits of a fast AO-loop rate on axial resolution and, consequently, on AO-corrected retinal image quality. We used the PARIS AO flood-illumination ophthalmoscope for this study, where retinal images from different focal planes at an AO-loop rate of 10 and 50 Hz were acquired.
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Adaptive optics ophthalmoscopy: Application to age-related macular degeneration and vascular diseases. Prog Retin Eye Res 2018; 66:1-16. [DOI: 10.1016/j.preteyeres.2018.07.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 07/12/2018] [Accepted: 07/12/2018] [Indexed: 12/11/2022]
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Gofas-Salas E, Mecê P, Petit C, Jarosz J, Mugnier LM, Montmerle Bonnefois A, Grieve K, Sahel J, Paques M, Meimon S. High loop rate adaptive optics flood illumination ophthalmoscope with structured illumination capability. APPLIED OPTICS 2018; 57:5635-5642. [PMID: 30118075 DOI: 10.1364/ao.57.005635] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The design and performance of an adaptive optics flood illumination ophthalmoscope (AO-FIO) platform, based on eye motion and dynamic aberrations experimental analysis, are described. The system incorporates a custom-built real-time controller, enabling up to 70 Hz loop rate without jitter, and an AO-corrected illumination capable of projecting high-resolution features in the retina. Wide-field (2.7°×5.4°) and distortionless images from vessel walls, capillaries, and the lamina cribrosa are obtained with an enhanced contrast and signal-to-noise ratio, thanks to careful control of AO parameters. The high spatial and temporal resolution (image acquisition up to 200 Hz) performance achieved by this platform enables the visualization of vessel deformation and blood flow. This system opens up the prospect of a return to favor of flood illumination adaptive optics systems provided that its high pixel rate and structured illumination capabilities are exploited.
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Lu J, Gu B, Wang X, Zhang Y. High speed adaptive optics ophthalmoscopy with an anamorphic point spread function. OPTICS EXPRESS 2018; 26:14356-14374. [PMID: 29877476 PMCID: PMC6005671 DOI: 10.1364/oe.26.014356] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 05/11/2018] [Indexed: 05/04/2023]
Abstract
Retinal imaging working with a line scan mechanism and a line camera has the potential to image the eye with a near-confocal performance at the high frame rate, but this regime has difficulty to collect sufficient imaging light while adequately digitize the optical resolution in adaptive optics imaging. To meet this challenge, we have developed an adaptive optics line scan ophthalmoscope with an anamorphic point spread function. The instrument uses a high-speed line camera to acquire the retinal image and act as a confocal gate. Meanwhile, it employs a digital micro-mirror device to modulate the imaging light into a line of point sources illuminating the retina. The anamorphic mechanism ensures adequate digitization of the optical resolution and increases light collecting efficiency. We demonstrate imaging of the living human retina with cellular level resolution at a frame rate of 200 frames/second (FPS) with a digitization of 512 × 512 pixels over a field of view of 1.2° × 1.2°. We have assessed cone photoreceptor structure in images acquired at 100, 200, and 800 FPS in 2 normal human subjects, and confirmed that retinal images acquired at high speed rendered macular cone mosaic with improved measurement repeatability.
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