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The Retina as a Window to the Brain—Reply

The Retina as a Window to the Brain—Reply In reply We would like to thank Dhillon and Dhillon for their interest in our recent article. We certainly agree with their observation that our findings of subtle vascular abnormalities in MS lesions detected at 7-T MRI “may have relevance to microvascular signs observed in the retina” because neurovascular abnormalities may provide insights into the pathogenesis of MS. Although retinal vasculitis has been found in 9% to 23% of patients with MS,1 most of the studies on retinal vascular abnormalities associated with MS were performed using fundus photography or fluorescein angiography. As Dhillon and Dhillon pointed out, the retina and brain may have a shared pathogenesis of MS. It has been reported that retinal venous sheathing is seen in patients with MS,2 and these perivenular abnormalities in a region free of myelin indicate that vascular changes may be a primary event of lesion formation in MS.3 In our article we demonstrated markedly improved detection of small venous vascular abnormalities associated with most MS lesions in the brain, with abnormal signals on and around the venous wall on 7-T MRI. This is due to the benefits of ultrahigh-field MRI, which provides a noticeably increased signal to noise ratio and enhanced susceptibility effects (sensitive to venous blood) that result in significantly improved image resolution (eg, 0.21 × 0.21 mm2) and contrast for small venous structures. Although ultrahigh-field (eg, 7-T) MRI is a powerful tool for assessing venous vasculature abnormalities in the early stages of lesion development in the brain, it has limited applications in retinal vascular imaging. First, while the sequence we used is highly sensitive to blood in small veins, it is also sensitive to the air-induced susceptibility artifacts. It is difficult to produce a good vascular image in the retina as we have done in the brain using this sequence because of the presence of air sinuses around the orbital and motion artifacts from the eyelid and globe. Second, it is more appropriate to use a surface orbital coil, which is inclusive of only the eye and not its surrounding tissues, to investigate the retina instead of the head coil we used because it provides better signal strength and fewer artifacts. Third, most MRI sequences developed for assessing retinal changes have thus far been used to focus on retinal layers but not venous vascular changes. For these reasons we do not have any retinal neurovascular images as good as our brain images for the patients we described. At the same time, however, it is important to not underestimate retinal imaging in evaluating MS-related retinal vascular changes. Further studies using suitable retinal imaging techniques combined with novel brain imaging will be required to elucidate the association between retinal vascular changes and brain lesion vascular activities.4 Correspondence: Dr Ge, Department of Radiology, Center for Biomedical Imaging, New York University School of Medicine, 650 First Ave, Sixth Floor, Room 615, New York, NY 10016 (yulin.ge@med.nyu.edu). Financial Disclosure: None reported. References 1. Engell TAndersen PK The frequency of periphlebitis retinae in multiple sclerosis. Acta Neurol Scand 1982;65 (6) 601- 608PubMedGoogle ScholarCrossref 2. Friedman SM Retinal vasculitis as the initial presentation of multiple sclerosis. Retina 2005;25 (2) 218- 219PubMedGoogle ScholarCrossref 3. Lightman SMcDonald WIBird AC et al. Retinal venous sheathing in optic neuritis: its significance for the pathogenesis of multiple sclerosis. Brain 1987;110 (pt 2) 405- 414PubMedGoogle ScholarCrossref 4. Patton NAslam TMacgillivray TPattie ADeary IJDhillon B Retinal vascular image analysis as a potential screening tool for cerebrovascular disease: a rationale based on homology between cerebral and retinal microvasculatures. J Anat 2005;206 (4) 319- 348PubMedGoogle ScholarCrossref http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Neurology American Medical Association

The Retina as a Window to the Brain—Reply

Archives of Neurology , Volume 65 (11) – Nov 10, 2008

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Publisher
American Medical Association
Copyright
Copyright © 2008 American Medical Association. All Rights Reserved.
ISSN
0003-9942
eISSN
1538-3687
DOI
10.1001/archneur.65.11.1548-a
Publisher site
See Article on Publisher Site

Abstract

In reply We would like to thank Dhillon and Dhillon for their interest in our recent article. We certainly agree with their observation that our findings of subtle vascular abnormalities in MS lesions detected at 7-T MRI “may have relevance to microvascular signs observed in the retina” because neurovascular abnormalities may provide insights into the pathogenesis of MS. Although retinal vasculitis has been found in 9% to 23% of patients with MS,1 most of the studies on retinal vascular abnormalities associated with MS were performed using fundus photography or fluorescein angiography. As Dhillon and Dhillon pointed out, the retina and brain may have a shared pathogenesis of MS. It has been reported that retinal venous sheathing is seen in patients with MS,2 and these perivenular abnormalities in a region free of myelin indicate that vascular changes may be a primary event of lesion formation in MS.3 In our article we demonstrated markedly improved detection of small venous vascular abnormalities associated with most MS lesions in the brain, with abnormal signals on and around the venous wall on 7-T MRI. This is due to the benefits of ultrahigh-field MRI, which provides a noticeably increased signal to noise ratio and enhanced susceptibility effects (sensitive to venous blood) that result in significantly improved image resolution (eg, 0.21 × 0.21 mm2) and contrast for small venous structures. Although ultrahigh-field (eg, 7-T) MRI is a powerful tool for assessing venous vasculature abnormalities in the early stages of lesion development in the brain, it has limited applications in retinal vascular imaging. First, while the sequence we used is highly sensitive to blood in small veins, it is also sensitive to the air-induced susceptibility artifacts. It is difficult to produce a good vascular image in the retina as we have done in the brain using this sequence because of the presence of air sinuses around the orbital and motion artifacts from the eyelid and globe. Second, it is more appropriate to use a surface orbital coil, which is inclusive of only the eye and not its surrounding tissues, to investigate the retina instead of the head coil we used because it provides better signal strength and fewer artifacts. Third, most MRI sequences developed for assessing retinal changes have thus far been used to focus on retinal layers but not venous vascular changes. For these reasons we do not have any retinal neurovascular images as good as our brain images for the patients we described. At the same time, however, it is important to not underestimate retinal imaging in evaluating MS-related retinal vascular changes. Further studies using suitable retinal imaging techniques combined with novel brain imaging will be required to elucidate the association between retinal vascular changes and brain lesion vascular activities.4 Correspondence: Dr Ge, Department of Radiology, Center for Biomedical Imaging, New York University School of Medicine, 650 First Ave, Sixth Floor, Room 615, New York, NY 10016 (yulin.ge@med.nyu.edu). Financial Disclosure: None reported. References 1. Engell TAndersen PK The frequency of periphlebitis retinae in multiple sclerosis. Acta Neurol Scand 1982;65 (6) 601- 608PubMedGoogle ScholarCrossref 2. Friedman SM Retinal vasculitis as the initial presentation of multiple sclerosis. Retina 2005;25 (2) 218- 219PubMedGoogle ScholarCrossref 3. Lightman SMcDonald WIBird AC et al. Retinal venous sheathing in optic neuritis: its significance for the pathogenesis of multiple sclerosis. Brain 1987;110 (pt 2) 405- 414PubMedGoogle ScholarCrossref 4. Patton NAslam TMacgillivray TPattie ADeary IJDhillon B Retinal vascular image analysis as a potential screening tool for cerebrovascular disease: a rationale based on homology between cerebral and retinal microvasculatures. J Anat 2005;206 (4) 319- 348PubMedGoogle ScholarCrossref

Journal

Archives of NeurologyAmerican Medical Association

Published: Nov 10, 2008

Keywords: brain,retina

References