Canis ISSN: 2398-2942

Optic neuritis

Contributor(s): David L Williams

Introduction

  • Inflammation of the optic nerve.
  • May involve the disk (papillitis) → becomes visible ophthalmoscopically.
  • If only retrobulbar portion of nerve affected → no fundoscopic changes.
  • A relatively common clinical entity in the dog, resulting in blindness (usually sudden onset).
  • Cause: primary cause often remains undiagnosed. Possible causes are:
    • Infectious agents (distemper, toxoplasma, fungi).
    • Toxins.
    • Trauma.
    • Generalized meningoencephally (GME).
  • Signs: sudden onset blindness.
  • Diagnosis: history, signs. A normal electroretinogram is observed in both bulbar and retrobulbar forms of optic neuritis Electroretinography.
  • Treatment: symptomatic, systemic high dose corticosteroids over several weeks.
  • Prognosis: poor, unless vision returns rapidly following treatment. Recurrence is likely.

Pathogenesis

Etiology

  • Difficult to diagnose underlying cause.
  • Following causes implicated:
    • Canine distemper.
    • Fungi (rare in UK, mainly in US).

Pathophysiology

  • Inflammation of the optic nerve, if not controlled → optic atrophy, secondary retinal atrophy and total blindness.
  • Usually bilateral.
  • Four anatomical parts to optic nerve:
    • Intra-ocular.
    • Intra-orbital.
    • Intracanalicular.
    • Intracranial.
  • Only pathology affectingintra-ocularpart is ophthalmoscopically visible.
  • Optic nerve is extension of brain, resembles white matter: nerve fibers are myelinated, supported by neuroglia, covered by three meningeal layers (dura, arachnoid, pia). CSF present in pia-arachnoid space.
  • Inflammatory process → demyelination → edema of surrounding tissues, possible hemorrhagic foci.

Timecourse

  • Acute onset.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers


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