What is Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)?

Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)

Non-arteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic neuropathy in patients over 50 years of age, characterized by sudden, painless vision loss due to ischemia of the optic nerve head. 1, 2

Definition and Epidemiology

• NAION represents one of the most important causes of blindness or severely impaired vision in middle-aged and elderly people 1
• It is the second most common cause of permanent optic nerve-related visual loss in adults after glaucoma 2
• The incidence is approximately 2.5-11.8 per 100,000 cases in men above 50 years 3
• More common in Caucasians compared to Asians 3

Clinical Presentation

• Sudden, painless, unilateral vision loss that occurs over seconds 2
• Variable visual field defect 2
• Relative afferent pupillary defect 2
• Swollen, hyperemic optic disc 2
• One or more flame-shaped peripapillary retinal hemorrhages may be present 2
• Impaired color vision proportional to visual acuity loss 4

Pathophysiology

• Caused by ischemic infarction of the optic nerve head, though the exact mechanism remains unclear 1
• Occurs primarily in patients with structurally small optic discs that have little or no cup ("disc at risk") 2
• Distinguished from arteritic anterior ischemic optic neuropathy (AION), which is caused by giant cell arteritis 5

Risk Factors

• Age over 50 years 1, 2
• Small optic disc with little or no physiologic cup 1, 2
• Systemic vascular conditions:
  • Hypertension 3
  • Diabetes mellitus 3
  • Hyperlipidemia 3
  • Obstructive sleep apnea 3
• Other risk factors:
  • Smoking 3
  • Optic nerve drusen 3
  • Certain medications including phosphodiesterase type 5 inhibitors (PDE-5I), amiodarone, and cabergoline 3
  • Possibly GLP-1 receptor agonists like semaglutide (though evidence is limited) 3

Diagnosis

• Clinical diagnosis based on characteristic presentation 1
• Important to differentiate from arteritic AION caused by giant cell arteritis, which requires urgent treatment 5
• Diagnostic workup should include:
  • Complete ophthalmologic examination 2
  • Visual field testing 2
  • Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to rule out giant cell arteritis 5
  • Neuroimaging (CT or MRI) may be used to rule out other causes of visual loss 5

Treatment and Management

• Currently, there is no proven effective medical or surgical therapy for NAION 1, 2
• Management focuses on:
  • Identifying and controlling underlying modifiable risk factors 1
  • Preventing development of NAION in the fellow eye 1
• Approximately 40% of patients experience spontaneous improvement in visual acuity 2
• Patients have a 15-19% risk of developing a similar event in the opposite eye over the subsequent 5 years 2

Special Considerations

• NAION must be distinguished from other causes of optic neuropathy, particularly arteritic AION, which requires urgent steroid treatment 5
• PDE-5 inhibitors have been associated with NAION, though the evidence shows no statistically significant increased risk (relative risk 1.02 [95% CI, 0.92 to 1.12]) 5
• High-altitude travel has been associated with development of NAION in some cases 5
• In perioperative settings, NAION can occur as a rare complication (perioperative ION), particularly in spine surgeries 5

Prognosis

• No consistently beneficial treatment exists 2
• About 40% of patients experience spontaneous improvement in visual acuity 2
• The condition typically does not progress after the initial event 2
• Prevention of fellow eye involvement is an important consideration 1, 2

Emerging Research

• Animal models have been developed that allow testing of various potential therapies 2, 6
• Research continues to explore neuroprotective strategies and treatments targeting the underlying vascular pathology 6