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      Application of Arterial Spin Labelling in Detecting Retinal Ischemia

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          Abstract

          Purpose: Here, we have tried to quantify the chorioretinal blood perfusion in patients who are clinically identified to be suffering from retinal ischemia using arterial spin labelling (ASL) MRI. Method: Four participants, diagnosed with retinal ischemia based on their structural OCT and angiography test, were then scanned using anatomical MRI as well as ASL. We optimized MR parameters to maximize resolution and target fixation, blinking, and breathing ques to minimize motion artifacts. Results: Participants had a maximum of ∼50 mL/100 mL/min of blood perfusion, which is below the normal values of ∼200 mL/100 mL/min. It also appeared that thinning of the choroid contributes more to the measured decreased chorioretinal perfusion, compared to slowed arterial filling time. Conclusion: Decreased chorioretinal perfusion is a multifactorial event and has been implicated in several posterior eye pathologies. Based on our current results, it seems that ischemia of the eye could be due to anatomy (tissue volume) and/or functionality (arterial flow).

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          Most cited references35

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          Enhanced depth imaging optical coherence tomography of the choroid in highly myopic eyes.

          To measure macular choroidal thickness (CT) in highly myopic eyes using enhanced depth imaging optical coherence tomography (OCT). Retrospective, observational case series. Enhanced depth imaging OCT images were obtained in highly myopic eyes (> or =6 diopters [D]). Images of CT were obtained by positioning a spectral-domain OCT device close enough to the eye to acquire an inverted image. CT was measured from the outer border of the retinal pigment epithelium to the inner scleral border at 1000-mum intervals of a horizontal section from 3 mm temporal to the fovea to 3 mm nasal to the fovea. Statistical analysis was performed to evaluate CT at each location and to correlate CT with age and refractive error. The mean age of the 31 patients (55 eyes) was 59.7 years (+/- 17.6 years; range, 24 to 90 years), and the mean refractive error was -11.9 D (+/- 3.7 D). The mean subfoveal CT was 93.2 microm (+/- 62.5 microm) and was correlated negatively with age (P = .006), refractive error (P < .001), and history of choroidal neovascularization (P = .013). Regression analysis suggested that subfoveal CT decreased by 12.7 mum for each decade of life and by 8.7 microm for each D of myopia. The choroid in highly myopic eyes is very thin and undergoes further thinning with increasing age and degree of myopia. Abnormalities of the choroid may play a role in the pathogenesis of myopic degeneration.
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            Ageing and degeneration in the macular region: a clinico-pathological study.

            S Sarks (1976)
            Clinical and pathological examination was performed on 378 eyes from 216 patients aged 43 to 97 years. This series represented eyes in which the fundi were normal or showed various manifestations of senile macular degeneration. The eyes were divided into six groups according to the histological appearance of a linear deposit at the base of the retinal pigment cells. Groups I and II were considered to represent normal ageing, Groups III and IV the progressive development of senile macular degeneration and Groups V and VI the end-results. Group I showed no basal linear deposit. Thickening and hyalinization of Bruch's membrane was noted as early as the fifth decade. Group II showed patchy development of the basal linear deposit in relation to thickened or basophilic segments of Bruch's membrane, or over intercapillary hyalinization extending to the level of the outer surface of the choriocapillaris. Almost all eyes in these two groups retained a normal fundus appearance but visual acuity declined with age even in the absence of other causes. In Group III the basal deposit formed a thin continuous layer associated with moderate degeneration of the retinal pigment epithelium. More than half the eyes had developed a clinical disturbance of pigmentation and in most vision was reduced. Group IV was characterized by thickening of the deposit and more pronounced disturbance of the pigment epithelium. Clinically most eyes showed coarse pigmentary changes and vision was in the order of 6/24. 14-3 per cent of eyes in this group showed early neovascularization from the choroid. In Group V the pigment epithelium disappeared to produce circumscribed areas of depigmentation. The basal linear deposit could be traced throughout the depigmented area in most eyes. Thin fibrovascular sheets were found beneath the pigment epithelium in 41-7 per cent of eyes. Group VI represented disciform degeneration. The basal linear deposit could often be demonstrated as a disrupted hyalinized layer incorporated into the scar. Disciform degeneration was an alternative end-result to geographical atrophy. In each group the clinical and histological findings may be modified by the presence of drusen or by atrophy of the choroid. The basal linear deposit consisted of banded fibres embedded in granular material lying between the plasma infoldings and the basement membrane of the retinal pigment epithelium. This deposit seems to be a manifestation of gradual failure of the pigment epithelium and proved to be the most suitable criterion by which to study the natural history of senile macular degeneration.
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              Information processing in the primate retina: circuitry and coding.

              The function of any neural circuit is governed by connectivity of neurons in the circuit and the computations performed by the neurons. Recent research on retinal function has substantially advanced understanding in both areas. First, visual information is transmitted to the brain by at least 17 distinct retinal ganglion cell types defined by characteristic morphology, light response properties, and central projections. These findings provide a much more accurate view of the parallel visual pathways emanating from the retina than do previous models, and they highlight the importance of identifying distinct cell types and their connectivity in other neural circuits. Second, encoding of visual information involves significant temporal structure and interactions in the spike trains of retinal neurons. The functional importance of this structure is revealed by computational analysis of encoding and decoding, an approach that may be applicable to understanding the function of other neural circuits.
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                Author and article information

                Journal
                COP
                COP
                10.1159/issn.1663-2699
                Case Reports in Ophthalmology
                S. Karger AG
                1663-2699
                2017
                September – December 2017
                14 December 2017
                : 8
                : 3
                : 545-557
                Affiliations
                [_a] aSchool of Optometry and Vision Science, University of Auckland, Auckland, New Zealand
                [_b] bAuckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
                [_c] cAuckland District Health Board Ophthalmology Services, Auckland, New Zealand
                Author notes
                *Dr. Ehsan Vaghefi, School of Optometry and Vision Science, University of Auckland, 85 Park Rd, Grafton, Auckland 1023 (New Zealand), E-Mail e.vaghefi@auckland.ac.nz
                Article
                485316 PMC5803724 Case Rep Ophthalmol 2017;8:545–557
                10.1159/000485316
                PMC5803724
                29422857
                526d6009-05fa-4df4-af88-c671a07ff789
                © 2017 The Author(s). Published by S. Karger AG, Basel

                This article is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC). Usage and distribution for commercial purposes requires written permission. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                History
                : 14 August 2017
                : 15 November 2017
                Page count
                Figures: 3, Tables: 2, Pages: 13
                Categories
                Case Report

                Vision sciences,Ophthalmology & Optometry,Pathology
                Chorioretinal blood flow,Arterial spin labelling,Chorioretinal ischemia

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