A 45-year-old man reported a dull ache behind his right eye upon eye movement, which had been occurring for 2 months. His BCVA was 20/20 OU. Pupils were equal and reactive to light. No noticeable relative afferent pupillary defect was observed. His only systemic condition of note was hypertension, which was well-controlled with medication.
Examination of the left eye was unremarkable. The right optic nerve was notably swollen inferiorly (Figure), which was confirmed with optic nerve head OCT. There was a dense inferior arcuate defect in the right eye.
The differential diagnoses considered included optic neuritis (ON), nonarteritic ischemic optic neuropathy (NAION), and compressive orbitopathy. Given the patient’s good cardiovascular health, NAION did not seem likely. Although NAION can occur in those younger than 50 years, the resulting vision loss is generally painless, and optic nerve edema tends to resolve over the course of 8 to 10 weeks.1 In this patient, the symptoms had been rather constant without significant improvement, and edema had persisted for at least 2 months.
In unilateral optic disc edema, it is important to rule out a compressive orbital lesion. This requires imaging of the orbits. MRI of head and orbits with and without contrast with fat suppression was the test of choice for this patient because contrast is needed to detect tumors and MRI is best for soft tissue imaging. No orbital mass was detected on MRI.
Pain from eye movement is present in more than 90% of patients with ON, making it the obvious diagnosis here.2 MRI supported the diagnosis and helped assess the risk for future development of multiple sclerosis. Patients with ON may have hyperintense white matter lesions on T2-weighted images elsewhere in the brain, which would indicate higher risk of multiple sclerosis.3
Fortunately, this patient did not have any such lesions on MRI.
Generally, idiopathic ON episodes self-resolve within 6 months of onset.4 This patient’s good vision throughout this episode suggests a good prognosis. Monitoring with dilated exams and visual field testing is important. A consultation with neuro-ophthalmology should be considered, but, given limited availability and long wait times, a lot of up-front legwork can be done by optometrists in such cases.
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