Discussion

Primary care and emergency medicine clinicians should familiarize themselves with common ophthalmologic conditions that, with timely referral and treatment, may help to improve vision. Ischemic optic neuropathies (ION) are the most common acute optic nerve pathology in patients older than 50 years of age, with an estimated incidence in this age group of 2.3 to 10.2 cases per 100,000 persons per year.1,2

Ischemic optic neuropathies are categorized as anterior (affects the anterior portion of the optic nerve) or posterior (affects the retrobulbar portion of the optic nerve) and arteritic or nonarteritic.1,2 Both arteritic and nonarteritic ION commonly present with anterior, optic disc involvement.

Arteritic anterior ischemic optic neuropathy (AAION) is a common cause of vision loss in patients with temporal arteritis.3 Thus, temporal artery biopsy should be used to rule out temporal arteritis if there is a strong clinical suspicion of this condition. Temporal arteritis is a medical emergency and requires prompt treatment to prevent blindness and stroke.3


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Nonarteritic, anterior ischemic optic neuropathy is the most common form of ischemic optic neuropathy.3,4 Typical presentation includes acute, unilateral, and painless loss of central and/or peripheral vision. Approximately 20% of patients with NAION present with visual acuity of 20/200 or greater at the time of their initial visit but visual acuity can vary from 30/64 or better in up to 50% of cases.1,3

Nonarteritic, anterior ischemic optic neuropathy can occur at any age although it is more common in older White adults (mean age of onset, 60 years) and is slightly more common in men than women.3 Medical history typically reveals risk factors for NAION such as cardiovascular disease, diabetes, hyperlipidemia, ischemic heart disease, hypertension, nocturnal hypotension, sleep apnea, stroke, and tobacco use.1 Patients with NAION usually present with a relative afferent pupillary defect (RAPD) and fundoscopic examination may reveal diffuse optic disc edema with superficial hemorrhages.2,3 These patients may also complain of dyschromatopsia.4

The underlying pathologic mechanism of NAION is not fully understood. Research suggests that this condition may occur because of a transient anterior optic nerve hypoperfusion, particularly at night because of nocturnal hypotension.1,2 Other research suggests that NAION may be caused by local or systemic disturbances in optic nerve head blood flow, as can be found with atherosclerosis, vasospasm, hypertension, and diabetes.5 For these reasons, some clinicians recommend that patients with these risk factors take antihypertension medications in the morning, rather than at bedtime.

Other medications that have been associated with NAION include the antiarrhythmic amiodarone and phosphodiesterase type-5 inhibitors (PDE-5i) used in the treatment of erectile dysfunction.5 The natural course of NAION may include variable visual improvement in up to 43% of patients without pharmaceutical intervention.6

Diagnostic Workup

The diagnosis of NAION is clinical with no specific laboratory testing or imaging recommended. However, patients with accompanying symptoms atypical for NAION or with risk factors for other comorbid conditions may warrant brain CT imaging to rule out other neurovascular pathology.4 Clinicians should refer these patients to an ophthalmologist as soon as possible for further work-up and management.

Treatment

Multiple medical and surgical treatment options for NAION have been tested but none have been definitively proven effective. However, intravitreal injections of short interfering ribonucleic acid (siRNA) are being investigated in ongoing clinical trials with limited data published to date.7,8 Retinal specialists have used systemic corticosteroid therapy to help reduce disc swelling and improve blood flow.6 Studies have demonstrated improvement in visual function with corticosteroid therapy compared with the natural course of NAION.6 However, these results are dependent upon initiating treatment as soon as possible at the onset of symptoms. Because the pathogenesis of NAION differs from cerebrovascular stroke, anticoagulation, thrombolytic therapy, and antiplatelet treatments are not recommended for NAION.6

Conclusion

Clinicians who encounter patients with possible NAION must first rule out AAION and other neurovascular pathologies. Management should be directed at evaluation and treatment of underlying risk factors that may have led to NAION development. Prompt referral to an ophthalmologist is warranted as well as consideration of the safety of continual use of PDE-5i medications in these patients. Although no clinical therapeutics have proven efficacious, oral corticosteroids may shorten the duration of optic disc edema, thereby leading to possible visual improvement. The prognosis of NAION is variable among patients. Fortunately, reoccurrence and contralateral eye involvement are rare.

Louise Lee, EdD, MHA, PA-C, is an associate professor and director of PA studies at St. John’s University in Queens, NY. Alison Ip, PharmD, is a pharmacist at Walgreens Pharmacy in Hicksville, NY.

References

1. Rucker JC, Biousse V, Newman NJ. Ischemic optic neuropathies. Curr Opin Neurol. 2004;17(1):27-35. doi:10.1097/00019052-200402000-00006

2. Biousse V, Newman NJ. Ischemic optic neuropathies. N Engl J Med. 2015;372(25):2428-2436. doi:10.1056/NEJMra1413352

3. Morrow MJ. Ischemic optic neuropathy. Continuum (Minneap Minn). 2019;25(5):1215-1235. doi:10.1212/CON.0000000000000767

4. Hayreh SS, Zimmerman B. Visual field abnormalities in nonarteritic anterior ischemic optic neuropathy: their pattern and prevalence at initial examination. Arch Ophthalmol. 2005;123(11):1554-62. doi:10.1001/archopht.123.11.1554

5. Campbell UB, Walker AM, Gaffney M, et al. Acute nonarteritic anterior ischemic optic neuropathy and exposure to phosphodiesterase type 5 inhibitors. J Sex Med. 2015;12(1):139-151. doi:10.1111/jsm.12726.

6. Nazari H, Berry S, Sadaka A, Lee AG, et al. The challenge of managing NAION. Retina Specialist. 2017;7(2):15-19.

7. Ahmed Z, Kalinski H, Berry M, et al. Ocular neuroprotection by siRNA targeting caspase-2. Cell Death Dis. 2011;2(6):e173.

8. Kupersmith MJ, Miller NR. A nonarteritic anterior ischemic optic neuropathy clinical trial: an industry and NORDIC Collaboration. J Neuroophthalmol. 2016;36(3):235-237. doi:10.1097/WNO.0000000000000409