Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)

Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)
SYMPTOMS Sudden painless vision loss that typically occurs upon wakening (About 50% see 20/40 or better), Loss of color vision (Severity is similar to the degree of vision loss)
SIGNS Typically unilateral
Segmental optic nerve edema, Optic nerve hyperemia, Loss of the cup, Blurring of the optic disc margins, Obscurations of the small vasculature at or around the optic nerve, Thickened and edematous retinal nerve fiber layer, Opacification of the retinal nerve fiber layer, Loss of sharp light reflexes around the optic disc, Splinter retinal hemorrhages, Cotton wool spots
The unaffected optic nerve is typically crowded and small in size. This is referred to as a "disc at risk"
Ultimately there will be optic nerve pallor with cupping following resolution of NAION or if NAION is chronic
WORK-UP Cranial nerve testing, Pupils (decrease in direct light response and an APD in the eye with the NAION), EOMs, Color vision (typically abnormal), Visual field (altitudinal defect that is typically inferior or sometimes a central defect ), Blood pressure evaluation (in order to rule out malignant hypertension), Slit lamp examination, Dilated retinal exam, Fundus photos, OCT, Fluorescein angiography (normal choroidal filling with delayed filling of the optic nerve vasculature)
OCT (Optic nerve analysis with EDI and RNFL analysis): *Elevation of the neuroretinal rim thickness *Smooth optic nerve contour *Elevation of the optic disc with involvement of the retinal nerve fiber layer with a smooth, hill-like appearance *Anterior displacement of the Bruch's/RPE complex especially near the Bruch's membrane opening *Presence of peripapillary hyper-reflective ovoid-mass like structures (PHOMS) which represent bulging optic nerve axons *Presence of subretinal fluid (presence of “lazy V sign” especially at the Bruch’s membrane opening) *Thickening of the of the RNFL with typically the nasal side being > 86 microns, temporal side being > 97 microns, superior side being > 149 microns, and inferior side being > 165 microns (Nasal RNFL thickening has the greatest specificity and sensitivity) *Subretinal hyporeflective space between the optic disc and Bruch's membrane opening (SHYPS) is >464 microns
TREATMENT Refer to a neuro-ophthalmologist/ER STAT for additional testing and treatment
Treatment and control of the underlying systemic conditions of the patient is key
Treatment with oral steroids remain controversial
If nocturnal hypotension secondary to hypertensive medications is suspected as an etiology of the NAION, taking the hypertensive medications earlier in the day should be considered
Erectile dysfunction drugs should be avoided
FOLLOW-UP After resolution of NAION, patient should be followed-up every 4-6 months
ADDITIONAL LAB | TESTS Testing will typically be ordered through the neuro-ophthalmologist/ER: MRI of the brain and orbits with and without contrast, ESR with C-reactive protein (will typically be normal), CBC with differential, PT/TT/BT/PTT/INR, Fasting blood sugar, HbA1c, Blood pressure evaluation, Sleep study
ETIOLOGY Idiopathic but thought to be due to lack of perfusion to the optic nerve because of involvement of the branches from the short posterior ciliary arteries
Typically associated with cardiovascular disease, hypertension, diabetes, sleep apnea, and nocturnal hypotension
DIFFERENTIAL DX Arteritic Anterior Ischemic Optic Neuropathy, Papilledema, Infiltrative optic neuropathy, Diabetic papillopathy, Hypertensive optic neuropathy
NOTES The profile of a typical patient with an NAION is a male over the age of 50 years old
OCT will go from showing swelling of the RNFL to thinning of the RNFL as optic atrophy develops
Visual prognosis is typically good
In 5 years, about 15% cases will become bilateral
Non-Arteritic Anterior Ischemic Optic Neuropathy: Superior optic nerve pallor following resolution of NAION with associated inferior altitudinal defect and superior RNFL thinning