Ranibizumab Therapy for Non-arteritic Ischemic Optic Neuropathy (NAION)

Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic neuropathy in people older than 50 years. It is characterized by sudden partial loss of vision in one eye and has an increased risk of vision loss in the fellow eye. Although cause has not been determined, NAION is thought to occur following an idiopathic ischemic event involving the short posterior ciliary arteries that supply blood to the most anterior part of the optic nerve. A complete loss of vision is rare, but partial loss of visual field or acuity can result from NAION in the affected eye(s).

Patients who have a 'disc at risk' or 'crowded disc' (small cup: disc ratio) are at increased risk for developing NAION. Other risk factors for NAION include age > 50 years and white race (estimated 95% of cases). Hypertension and diabetes also predispose to NAION development. Other factors that have been associated with NAION include high cholesterol, arteriosclerosis, stroke, cardiac and intraocular surgery, tobacco use, nocturnal hypotension, blood loss, glaucoma, elevated homocysteine and sleep apnea. The association between NAION and hypertension, high cholesterol and diabetes is stronger in individuals younger than 50 years than in older persons.

Patients with NAION caused by ischemia leading to swelling of the optic nerve and rapidly progressing visual loss have had limited results with therapy such as corticosteroids, brimonidine, levodopa or surgery, such as optic nerve sheath decompression, in the past. Currently, there is no standard of care for these patients.

Although the role of vascular endothelial growth factor (VEGF) in NAION has not been established, ischemic conditions may lead to VEGF production which could be the cause of edema and swelling. This possibility suggests that VEGF may be a target for therapeutic intervention by ranibizumab. Ranibizumab has demonstrated an effect on edema and vascular permeability. In animal studies it has shown a concentration- dependent effect of blunting the vascular permeability induced by VEGF. Of the more than 5,000 subjects with age-related macular degeneration in current and completed clinical trials, vascular permeability and edema have decreased with the use of ranibizumab.