Vitreopapillary Findings in Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)
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Vitreopapillary Findings in Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)

  • Definition and Epidemiology of NAION:
    • NAION is the second most common optic neuropathy in adults, typically affecting individuals around 50 years of age.
    • Prevalence: 2–10 per 100,000 population.
    • Low recurrence rate ipsilaterally (6.4%) but significant contralateral risk (20%).
  • Clinical Features:
    • Presents with sudden, painless vision loss, often with an inferior altitudinal visual field defect.
    • Associated with crowded optic discs (small cup-to-disc ratio), increasing susceptibility to ischemia.
    • Risk factors include hypertension, hypercholesterolemia, and age >50.
  • Pathogenesis:
    • Caused by hypoperfusion and segmental infarction of the optic nerve head.
    • The exact trigger for vascular impairment remains unclear; traditional theories involve ischemia-induced axon swelling causing a compartment syndrome in the scleral canal.
    • Limitations of traditional theories: Cannot explain why NAION does not occur in papilledema (where more compression exists) or why it selectively affects older adults despite axonal loss from aging.

 

  • Vitreopapillary Interface Hypothesis:
    • Proposed by Dr. Hoyt (2015): Vitreopapillary interface changes during posterior vitreous detachment (PVD) may trigger NAION in crowded discs.
    • Focal vitreopapillary attachments (tufts) transmit tractional forces to optic nerve vasculature, potentially inducing vasospasm.
    • Crowded discs have stronger vitreopapillary attachments due to increased astrocytes (8–16% of optic nerve head) and their extensions through basal lamina defects.
  • Study Design:
    • Retrospective analysis of 32 NAION eyes with crowded discs using high-resolution OCT, compared to:
      • 31 eyes with crowded discs (control).
      • 32 eyes without crowded discs (control).
    • Outcome measures: Incidence of PVD, vitreopapillary/vitreovascular attachments, and epipapillary membranes.
    • Control eyes sourced from neuro-ophthalmology clinic (e.g., migraine, cluster headache patients).
  • Key Findings:
    • No difference in posterior vitreous separation over the macula across groups.
    • Higher rate of posterior hyaloid attachment to the optic nerve in crowded discs (lower progression from stage 3 to stage 4 PVD).
    • Increased focal vitreopapillary attachments in crowded discs compared to non-crowded discs.
    • In NAION, focal vitreovascular attachments are more prominent and closely associated with optic nerve vessels, transmitting tractional forces that may trigger vasospasm.
    • Only 1 in 20 crowded discs develops NAION, likely due to specific vitreovascular attachments near optic nerve vessels.
  • Diagnostic Implications:
    • OCT is critical for assessing optic nerve edema, retinal nerve fiber layer thickness, and vitreopapillary attachments in NAION.
    • Focal vitreopapillary attachments near blood vessels are a distinguishing feature in NAION versus crowded discs without NAION.
    • Limitations of perfusion studies (e.g., fluorescein angiography, ICG, OCT-A): Peripapillary edema or atrophy can mask or mimic hypoperfusion.
  • Progression of PVD:
    • PVD begins in the first/second decade, starting in the mid-periphery, progressing anteriorly and posteriorly.
    • Over the optic disc, PVD starts superior temporally (weakest attachment) and progresses to inferonasal (strongest), explaining inferior defects in NAION.
    • Vitreous remains attached to the optic nerve until stage 4 PVD.
  • Mechanistic Insights:
    • Optic nerve astrocytes and vascular endothelium are mechanosensitive, responding to traction with altered protein expression (e.g., endothelin-1, renin-angiotensin system), potentially inducing vasospasm.
    • Crowded discs have a higher proportion of astrocytes, increasing vitreovascular connections.
  • Clinical Relevance:
    • NAION diagnosis is descriptive; no definitive diagnostic test exists.
    • Most NAION patients in the study had vitreopapillary attachments during the acute phase, with PVD developing later.
    • Case example: OCT showed vitreopapillary traction deforming a vessel, correlating with NAION onset, resolving post-PVD.
  • Future Directions:
    • Animal models are needed to replicate vitreopapillary traction and study NAION triggers (current models focus on thrombosis, not traction).
    • Potential for identifying at-risk individuals (crowded discs with vitreovascular attachments) for close monitoring or prophylactic interventions (e.g., vitrectomy).
  • Board-Relevant Takeaways:
    • NAION is a clinical diagnosis based on history, visual field defects, and optic disc appearance (crowded disc, edema).
    • OCT findings of vitreopapillary traction near vessels are a novel risk factor for NAION in crowded discs.
    • Differential diagnosis includes arteritic ischemic optic neuropathy (e.g., GCA), optic neuritis, and papilledema.

Citation of the Paper

Tezel, T. H., Muazami, G., Hondur, A., & Hondur, G. (2024). Vitreopapillary findings in non-arteritic anterior ischemic optic neuropathy versus healthy eyes. Ophthalmology, September issue. Available at: aaojournal.org