Case Report of Non-Arteritic Ischemic Optic Neuropathy (NAION)
Title: Case Report of Non-Arteritic Ischemic Optic Neuropathy (NAION)
Author (s): Eileen Hwang, Judith Warner
Photographer (s): Mel Chandler, Cyrie Fry
Keywords/Main Subjects: NAION, non-arteritic ischemic optic neuropathy, visual field defect, optic disc edema, optic nerve edema, optic neuropathy, afferent pupillary defect
Diagnosis/Differential Diagnosis: non-arteritic ischemic optic neuropathy
Chief complaint: visual field defect
History of present illness: The patient is a 73-year-old woman who presented two days after sudden onset of vision changes. She described a gray film in the inferior area of the vision in her right eye that had not changed since onset. The patient denied having fevers, chills, weight loss, jaw claudication, shoulder stiffness and weakness. Her medical history was significant for hypertension, hyperlipidemia, and rheumatoid arthritis, and her medications included enalapril 20 mg twice a day, hydrochlorothiazide 10 mg daily in the morning, and aspirin 81 mg daily. She was in the habit of measuring her blood pressure daily and reported that it was consistently in the 130s/50s-60s. She denied feeling lightheaded when standing up. She denied snoring.
Initial examination: The patient’s visual acuity was 20/20 in each eye with pin hole and she did not have a relative afferent pupillary defect. She had mild elevation without edema of the superior optic disc in the right eye and a retinal nerve fiber layer hemorrhage nasal to the disc (Figure 1). Her cup-to-disc ratio in the right eye was 0.2. The cup-to-disc ratio in her left eye was 0.6. The patient was referred to glaucoma, and subsequently to neuro-ophthalmology.
Follow up examination in the neuro-ophthalmology clinic: Two weeks later, the patient’s visual acuity with pinhole was 20/20 in the right eye and 20/20 in the left eye. She had a 0.6 log unit right relative afferent pupillary defect. Her color vision was decreased on the right with 80% red desaturation and 11/13 Ishihara plates compared to 13/13 on the left. Her critical flicker fusion frequency was 39 Hz on the right and 41 Hz on the left. On slit lamp examination, there was 350 degrees of disc edema in the right eye with obscuration of the nasal vessels. There were also exudates on the nasal disc and a retinal nerve fiber layer hemorrhage nasal to the disc (Figure 2). On Humphrey visual field testing, there was an inferior arcuate defect in the right eye. The left eye visual field showed an inferior rim artifact (Figure 3).
Clinical course: The patient was diagnosed presumptively with non-arteritic ischemic optic neuropathy although other possibilities that were considered were a compressive mass lesion, central retinal vein occlusion, diabetic papillitis, hematological abnormalities (thrombocytosis, anemia), vasculitis, and hypertensive papillitis. Lab tests were performed to rule out giant cell arteritis, and causes of hypercoagulability such as thrombocytosis, polycythemia, and multiple myeloma. The results of these laboratory studies (erythrocyte sedimentation rate, c-reactive protein, complete blood count, and serum protein electrophoresis) were normal.
The patient decided to start brimonidine twice daily for neuro-protection after an informed discussion about the limited evidence supporting its use. In conjunction with her primary care doctor, she decreased her enalapril to once a day in the morning. Her diastolic blood pressure remained in the 50s-60s.
Four weeks after initial symptom onset, the patient reported that the visual field defect had suddenly extended to include part of her central vision. Her visual acuity was stable, but the magnitude of her right relative afferent pupillary defect increased to 0.9 log units and her color vision worsened to 5/13 Ishihara plates. On slit lamp examination, her optic nerve edema had almost completely resolved except for mild blurring of the margin inferiorly. Humphrey visual field testing demonstrated a new superior paracentral scotoma with improvement of the inferior altitudinal defect. Due to the unusual nature of her late progression and the lack of a “disc at risk” (i.e. small cup to disc ratio) in the contralateral eye, the decision was made to order cerebral imaging to rule out a compressive or infiltrative lesion.
Anterior ischemic optic neuropathy (AION) is characterized by rapid onset of unilateral vision loss associated with optic nerve edema. There are two types of anterior ischemic optic neuropathy – arteritic anterior ischemic optic neuropathy (AAION), and non-arteritic anterior ischemic optic neuropathy (NAION). To make a diagnosis of NAION, AAION should be sufficiently ruled out, which can be by a history negative for symptoms of temporal arteritis (headache, scalp tenderness, jaw claudication, fever, weight loss, and proximal joint pain) and young age (less than 50 years old), but also by laboratory testing or temporal artery biopsy, depending on the level of clinical suspicion. In the evaluation of a patient with acute onset of unilateral vision changes and optic nerve edema, optic neuritis must also be considered, and characteristics such as a younger patient age and pain with eye movements are suggestive of optic neuritis rather than NAION.
After acute onset, the vision loss usually remains static, although it can also progress in either a gradual or stepwise fashion for a few weeks before stabilizing. On examination, there is optic nerve edema that can be segmental and usually is not chalky white. Peripapillary hemorrhages are common. The optic nerve in the contralateral, unaffected eye usually has a small cup-to-disk ratio, and this is thought to contribute to risk of NAION because the crowding supports propagation of ischemia and swelling. Visual field defects due to NAION are most commonly altitudinal, although many other types of defects can be present as well.
Fluorescein angiography in patients with acute NAION demonstrates delayed filling of the prelaminar optic disc, supporting the role of anterior ischemia in the pathogenesis of NAION. Possible risk factors for NAION that may exacerbate optic nerve ischemia include nocturnal hypotension and sleep apnea. Recently, it has been demonstrated that erectile dysfunction medications increase the risk of NAION, although this is a very rare event (Campbell, 2015). After NAION has been diagnosed, interventions should focus on minimizing risk factors, since there are no acute interventions that have been shown to improve outcomes. There is poor evidence that brimonidine eye drops or oral low-dose aspirin can prevent future events in the contralateral eye (Kupersmith, 1997), but at our institution, brimonidine is usually started in both eyes for its neuroprotective effect. It is usually stopped in the acutely affected eye after the optic nerve edema has resolved since that disc is no longer at risk for NAION secondary to atrophy but continued in the unaffected eye. Low dose aspirin is usually recommended as well.
Visual acuity and visual field defects can improve somewhat in the months following the initial onset, but usually do not return to baseline. There is rarely ever progression beyond 2 months, and therefore any evidence of progression should be an indication to look for other causes of unilateral optic nerve edema, such as a mass lesion or intraocular inflammation.
Miller NR, Newman NJ, Biousse V, Kerrison JB, Editors. Walsh and Hoyt’s Clinical Neuro-ophthalmology. Lippincott Williams & Wilkins, Philadelphia, 2005.
Campbell UB, Walker AM, Gaffney M, Petronis KR, Creanga D, Quinn S, Klein BE, Laties AM, Lewis M, Sharlip ID, Kolitsopoulos F, Klee BJ, Mo J, Reynolds RF. Acute nonarteritic anterior ischemic optic neuropathy and exposure to phosphodiesterase type 5 inhibitors. J Sex Med. 2015 Jan;12(1):139-51.
Kupersmith MJ, Frohman L, Sanderson M, Jacobs J, Hirschfeld J, Ku C, Warren FA. Aspirin reduces the incidence of second eye NAION: a retrospective study. J Neuroophthalmol. 1997 Dec;17(4):250-3.
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