Anterior ischemic optic neuropathy (AION) is the most cause of altitudinal defect: a loss of vision in the upper or lower horizontal half of the visual field.
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Visual Field Defect: Altitudinal Hemianopia
anterior ischemic optic neuropathy (AION)
Most commonly due to vascular accidents, much less commonly due to trauma (accidental or compressive).
AION is divided into: Non-Arteritic (NAION) and Arteritic (AAION) forms.
Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)
- Presents as a sudden, unilateral, painless loss of vision (c/o waking up with vision loss).
- Typically occurs in patients > 50 or older.
- Vasculopathic risk factors include: hypertension, diabetes mellitus, nocturnal hypo-tension, obstructive sleep apnea, hypotension during prolonged surgeries, arteriosclerosis.
- Ophthalmoscopic exam shows: segmental or total disc edema and the opposite eye shows a "disc at risk (crowded"
- Pupillary testing shows an relative afferent pupillary defect.
- Differentiated from optic neuritis in that patients are typically older, have vascular risk factors, it's painless and yet the longterm likelihood of recovery is worse.
- Similar loss of vision compared NAION but patients often have episodes of amaurosis fugax as a warning sign prior to the ultimate loss of vision.
- Age of presentation is typically older than NAION (usually occurs in the elderly).
- Associated with systemic findings of inflammation from, most commonly, Giant cell arteritis (large- and medium-sized head and neck artery vasculitis). Vision loss comes from Giant cell arteritis involvement of the posterior ciliary artery, which feeds the optic nerve head.
- Vision loss is typically worse than NAION, ultimately, with pale optic nerve head (chalky).
- Patients should be treated with steroids prior to testing, which includes: ESR (or CRP) and temporal artery biopsy. Steroids will not affect the temporal artery biopsy, if done within a reasonable time period (days).