Advances in neuroimaging of the visual pathways and their use in glaucoma

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Abstract

Recently developed neuroimaging techniques such as diffusion tensor (DT) magnetic resonance (MR) imaging, functional MR imaging (fMRI), and MR spectroscopy can be used to evaluate the microstructural integrity of white-matter fibers and the functional activity of gray matter. They have been widely employed to investigate various diseases of the central nervous system, and they can be useful tools for assessing the integrity and functional connections of the visual pathways and areas that play key roles in glaucoma. In vivo degeneration of the optic nerves can be noninvasively demonstrated by DT MR imaging. DT fiber tractography provides valuable information on the axonal density of postgeniculate fibers (optic radiation), and fMRI studies of patients with primary open-angle glaucoma (POAG) have demonstrated alterations involving the human visual cortex that are consistent with clinically documented losses of visual function. This article reviews some of the more recent data supporting the use of MR imaging techniques as reliable, noninvasive tools for monitoring the progression of human glaucoma.

Introduction

Recently developed neuroimaging techniques such as diffusion tensor (DT) magnetic resonance (MR) imaging and functional MR imaging (fMRI) can be used to evaluate the microstructural integrity of white-matter fibers and the functional activity of gray matter. Their introduction has allowed a reexploration of the normal anatomy of white-matter tracts in the living human brain and the elaboration of connectional models of brain function. During the last 10 years, these techniques have also been used for the in vivo study of a variety of brain pathologies. First used in the investigation of ischemic stroke, they are now becoming increasingly important in the evaluation of intracranial neoplasms, inflammatory disorders, developmental anomalies of the central nervous system (CNS), and neurodegenerative diseases.

Both techniques can also be utilized to investigate the integrity and functional connections of the visual pathways, including areas that play key roles in glaucoma: pre- and postgeniculate white-matter fibers, the lateral geniculate nuclei (LGNs), and various areas of the visual cortex. This article provides an overview of some of the newer MRI techniques being used in neuro-ophthalmology and their specific applications in the study of patients with glaucoma.

Section snippets

Conventional MR imaging and the visual pathways

The macroscopic anatomy of the visual system can be demonstrated and assessed in vivo with conventional MR imaging. The optic nerve is a white-matter tract that is sheathed by the leptomeninges and dura mater, and its subarachnoid space is continuous with the intracranial subarachnoid space. On oblique coronal MR images, the intraorbital segment of the optic nerve ranges in thickness from 3.1 (anteriorly) to 2.5 mm (posteriorly), whereas the mean dural diameter measures between 5.1 (anteriorly)

Diffusion MR imaging

Diffusion is a random process that results from the thermal translational motion of molecules. In biological tissues, water diffuses inside, outside, around, and through cellular structures. Cellular membranes hinder these movements and force the water to take more tortuous paths. Diffusion is restricted by the presence of cellular swelling or increased cellularity, whereas necrosis, which involves the breakdown of cellular membranes, decreases diffusion-path tortuosity and increases apparent

Functional MR imaging

fMRI involves the application of MR techniques for high-resolution (spatial and temporal) investigations of brain physiology. Local changes in cerebral hemodynamics are closely linked to local cerebral activity, and they can be assessed with the technique known as blood oxygen level–dependent (BOLD) fMRI. The BOLD contrast effect depends on changes in the deoxyhemoglobin content of blood during states of increased neuronal activity (Ogawa et al., 1990). Many studies have been performed to

Proton MR spectroscopy

MR spectroscopy is a noninvasive tool for investigating the chemical environment of the brain. The proton MR spectrum is characterized by at least three peaks, which represent (1) the compounds creatine and phosphocreatine (Cr), which are generally associated with cellular energy metabolism; (2) choline (Cho), which is associated with cell membrane synthesis; and (3) N-acetyl aspartate (NAA), a marker of neuronal integrity. Several studies have demonstrated the usefulness of MR spectroscopy in

References (45)

  • A. Miki et al.

    Detection of visual dysfunction in optic atrophy by functional magnetic resonance imaging during monocular visual stimulation

    Am. J. Ophthalmol.

    (1996)
  • V. Oertel et al.

    Visual hallucinations in schizophrenia investigated with functional magnetic resonance imaging

    Psychiatry Res.

    (2007)
  • S.A. Trip et al.

    Optic nerve diffusion tensor imaging in optic neuritis

    Neuroimage

    (2006)
  • Q. Wu et al.

    MR diffusion changes correlate with ultra-structurally defined axonal degeneration in murine optic nerve

    Neuroimage

    (2007)
  • J. Alvarez-Linera Prado et al.

    Functional magnetic resonance imaging of the visual cortex: relation between stimulus intensity and bold response

    Rev. Neurol.

    (2007)
  • P.A. Bandettini et al.

    Time course EPI of human brain function during task activation

    Magn. Reson. Med.

    (1992)
  • P.J. Basser

    Inferring microstructural features and the physiological state of tissues from diffusion-weighted images

    NMR Biomed.

    (1995)
  • F. Boller et al.

    Disorders of visual behavior

  • C.C. Boucard et al.

    Occipital proton magnetic resonance spectroscopy (1H-MRS) reveals normal metabolite concentrations in retinal visual field defects

    PLoS ONE

    (2007)
  • L.A. Brandão et al.

    MR Spectroscopy of the Brain

    (2004)
  • T.E. Conturo et al.

    Tracking neuronal fiber pathways in the living human brain

    Proc. Natl. Acad. Sci. U.S.A.

    (1999)
  • Q. Dong et al.

    Clinical applications of diffusion tensor imaging

    J. Magn. Reson. Imaging

    (2004)
  • Cited by (0)

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