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Nonarteritic anterior ischemic optic neuropathy: Clinical features and diagnosis

Nonarteritic anterior ischemic optic neuropathy: Clinical features and diagnosis
Literature review current through: Jan 2024.
This topic last updated: Feb 11, 2020.

INTRODUCTION — Ischemic optic neuropathy is the most common optic nerve disorder in patients over age 50 years. A recent population-based study from Korea found an incidence of 11.3 amongst 100,000 individuals of nonarteritic anterior ischemic optic neuropathy (NAION) [1]. Ischemic optic neuropathy is generally categorized as anterior (affecting the optic disc) versus posterior (retrobulbar) and as arteritic versus nonarteritic. Anterior involvement is common with both arteritic and nonarteritic ischemic optic neuropathy.

NAION is the most common form of ischemic optic neuropathy. It is an idiopathic, ischemic insult of the optic nerve head characterized by acute, monocular, painless visual loss with optic disc swelling.

This topic will discuss the clinical features and diagnosis of NAION. The epidemiology, pathogenesis, etiologies, prognosis, and treatment of NAION are discussed separately. Other forms of ischemic optic neuropathy and other optic neuropathies are discussed separately. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies" and "Nonarteritic anterior ischemic optic neuropathy: Prognosis and treatment" and "Clinical manifestations of giant cell arteritis" and "Optic neuropathies".)

CLINICAL FEATURES

Presenting symptoms — Patients describe monocular loss of vision occurring over hours to days. Symptoms were present upon awakening in as many as 73 percent of patients according to some reports; however, in the Ischemic Optic Neuropathy Decompression Trial (IONDT), symptoms first present on awakening were reported in just 42 percent [2,3]. Some patients report altitudinal (often inferior) vision loss or a scotoma. It is common for visual loss to progress over the first few days; in one study the average time to peak vision loss was approximately five days [4]. Most patients stabilize in one to two weeks [2,5].

It is rare for the symptoms to occur in both eyes at the same time. In one series, 11 percent had a bilateral presentation, but most of these cases occurred in the setting of severe blood pressure fluctuations (eg, surgery, dialysis) [6]. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Etiology and risk factors'.)

Prodromal ocular or systemic symptoms are atypical for NAION and suggest an alternative etiology such as giant cell arteritis. However, in the IONDT, 5 percent reported that their symptoms were intermittent at onset [2].

Pain is not typical, but some ocular discomfort has been reported in 8 to 12 percent of individuals [2,4,7]. If pain is a prominent complaint, NAION is less likely to be the diagnosis than optic neuritis or giant cell arteritis (arteritic ischemic optic neuropathy).

Examination findings — Examination of patients with NAION typically reveals:

Reduced visual acuity

Dyschromatopsia (diminished color vision)

Afferent pupillary defect

Optic disc edema (picture 1)

Peripapillary splinter hemorrhage

Small optic cup, nerve fiber crowding in the unaffected eye (picture 2)

An entity of so-called incipient NAION has been described in patients who are found on examination to have unilateral optic disc edema [8-10]. Such patients are typically seen in follow-up after a previous episode of NAION in the other eye or for unrelated conditions (eg, diabetic retinopathy). In one series, 25 percent of such patients progressed to symptomatic NAION over a few to several weeks, and a subsequent episode of NAION in that eye occurred in an additional 20 percent [8]. Fluorescein angiography has confirmed filling defects consistent with impaired perfusion in a patient with presymptomatic phase of NAION [11].

A relative afferent pupillary defect is an invariable manifestation of NAION, as with other optic neuropathies. However, the finding may be subtle if the injury is not severe or if there was previous NAION in the other eye [12].

Optic disc appearance — In contrast to giant cell arteritis, the optic disc edema in NAION tends to be hyperemic (picture 1) rather than pallid (picture 3). In the IONDT, optic nerve head swelling was diffuse in 75 percent and segmental in 25 percent of patients [2]. Segmental disc edema usually involves the superior portion of the disc; this anatomic distribution has been attributed to the anatomic division of the circle of Zinn-Haller (see "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Vascular anatomy'). Segmental disc edema may not correspond to distribution of vision loss.

Disc hyperemia with peripapillary splinter or flame hemorrhages and dilated telangiectatic capillaries is common and was seen in 72 percent of patients in IONDT (picture 4) [2]. These features may represent microvascular shunting from ischemic to nonischemic regions of the optic nerve head. The retinal arterioles are typically narrowed focally in the peripapillary region in up to 68 percent of affected patients [13].

The fellow eye will often reveal a crowded optic nerve head with small or absent physiologic cup (picture 2) [14-17]. This disk appearance has been denoted the "disk at risk" (see "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Ocular risk factors'). In one case series, this finding was noted in 82 percent of cases [6]. Alternatively, the fellow eye may demonstrate optic disc pallor that suggests a prior episode of NAION; in the IONDT, 94 of 420 patients (23 percent) had this finding; 61 of these patients reported a known history of NAION in that eye [2].

Vision loss — Visual acuity loss in NAION is on average less severe than in arteritic ischemic optic neuropathy, but can range from 20/20 to no light perception. Visual acuity is better than 20/60 in 31 to 52 percent of patients, and is better than 20/200 in one-half to two-thirds of patients [2,4,5,12,18,19]. Some patients with NAION may have normal visual acuity (20/20 or better) [20].

Color vision is diminished in almost all patients in the affected eye. The color vision loss seems to correlate with the degree of vision loss. By contrast, patients with optic neuritis may have profound color vision loss with relatively good visual recovery.

An inferior altitudinal visual field defect is the classically described field defect seen in NAION, but among reported case series, its prevalence varies from 25 to 79 percent [18,21,22]. In one series of perimetry studies in 312 eyes, a variety of visual field defects were observed, with an absolute inferior altitudinal defect observed in only 8 percent [21]. The single most commonly observed defect was an inferior nasal defect, found in 22 percent. Other common defects included central, centrocecal, and arcuate scotomas, as well as generalized depression.

DIFFERENTIAL DIAGNOSIS — NAION must be differentiated from other entities such as idiopathic, demyelinating, other inflammatory, compressive, and infiltrative optic neuropathies; most of these entities can be differentiated from NAION based on history and ophthalmoscopic disc appearance.

The major diagnostic consideration is giant cell arteritis or arteritic anterior ischemic optic neuropathy. This also primarily affects older adults, usually over the age of 70 years, and the clinical presentation can be similar. One distinguishing feature of giant cell arteritis is a prodrome of systemic symptoms known as polymyalgia rheumatica, which include jaw claudication, proximal myalgias and arthralgias, scalp tenderness, headache, and fatigue. Disc edema tends to be pallid rather than hyperemic (picture 1 and picture 3), and transient prodromal vision loss is more common in giant cell arteritis than in NAION. The diagnosis of giant cell arteritis typically requires a temporal artery biopsy. (See "Clinical manifestations of giant cell arteritis".)

Optic neuritis can also present with acute monocular vision loss with disc edema. In comparison with NAION, patients tend to be younger (usually 18 to 40 years) and pain is usually a prominent feature.

There are numerous other causes of optic nerve disease (table 1). Some of the clinical features of the more common disorders are contrasted in the table (table 2); these are discussed in more detail separately. (See "Optic neuropathies".)

DIAGNOSIS — The diagnosis of NAION in the majority of patients is clinical, based upon age, presence of vasculopathic risk factors, the pattern of visual loss, and the appearance of the swollen disc. A medical history of conditions associated with NAION, (eg, obstructive sleep apnea, use of erectile dysfunction drugs) should be sought. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies".)

Arteritic (eg, giant cell arteritis) ischemic optic neuropathy should be considered and ruled out. Older adult patients with anterior ischemic optic neuropathy should be questioned regarding headache, scalp tenderness, and jaw claudication for giant cell arteritis. In patients older than 55 years, an erythrocyte sedimentation rate (ESR) and C-reactive protein levels are obtained. Temporal artery biopsy should be considered if these are abnormal or if there is a high clinical suspicion for giant cell arteritis because of suggestive symptoms such as headache or jaw claudication (table 2). (See "Diagnosis of giant cell arteritis".)

Otherwise, no other testing is required for patients with typical features of NAION. The following features are atypical and suggest the need for further testing [23]:

Age less than 50 years

Absence of vasculopathic risk factors

Large cup-to-disc ratio in the unaffected eye

Hemianopic visual field loss

Bilateral simultaneous or rapidly sequential anterior ischemic optic neuropathy

Transient visual loss preceding visual loss

No optic disc edema in acute phase

Progression after two to four weeks

Recurrence in same eye

Inflammation in anterior or posterior segment

Optic atrophy at presentation

If atypical features exist, neuroimaging should be performed to rule out other orbital or intracranial causes. In particular, contrast-enhanced magnetic resonance imaging (MRI) may be useful in younger patients to differentiate NAION and optic neuritis [12,24,25]. While 95 percent of patients with optic neuritis will demonstrate gadolinium contrast enhancement of the optic nerve, this is relatively unusual (<10 percent) in NAION. MRI is also useful to evaluate for compressive and infiltrative optic neuropathies. (See "Optic neuropathies".)

ADDITIONAL EVALUATION — Further evaluation in patients with NAION focuses on identifying potential underlying causes and risks factors, particularly those that are modifiable (table 3). (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Etiology and risk factors'.)

Generally, carotid Doppler studies and cardiac echocardiography are not indicated for NAION, since embolism is not causative in the vast majority of cases [26]. Magnetic resonance imaging (MRI) and magnetic resonance angiography of the cervical carotid artery may be considered to rule out carotid dissection if there is neck pain, antecedent trauma, or other suggestive features of this diagnosis. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Pathogenesis'.)

Fluorescein angiography often reveals delayed filling of the prelaminar layers of the edematous optic disc in acute NAION [27,28]. Poor or absent filling of the choroid is not typical of NAION and suggests giant cell arteritis [28].

In acute stages of NAION, optical coherence tomography (OCT) will show thickness of the inner and outer layers of the peripapillary retina, while in chronic cases, atrophy of the ganglion cell layer and its axons is seen as inner retinal thinning [29]. OCT angiography (OCT-A) has shown a decreased circum papillary vessel density in acute and old NAION cases [30-34]. The blood flow impairment seen on OCT-A corresponds to structural OCT deficits of the retinal nerve fiber layer (RNFL) and ganglion cell layer complex (GCC), as well as to automated visual field deficits in 90 percent of eyes in one study [30]. Another observational study of 10 patients, however, did not find any correlation of radial capillary network changes to visual field defects [35].

Measurement of 24-hour blood pressure may identify individuals with nocturnal hypotension (believed to be a risk factor for NAION), but limited treatment options are available for patients at risk [36]. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Nocturnal hypotension'.)

Hypercoagulable studies are generally recommended only if there is a past medical or family history suggesting a thrombogenic tendency, but they should also be considered in young patients (<55 years) without vascular risk factors [6,37-40]. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Prothrombotic risk factors'.)

We typically order polysomnography to evaluate for sleep apnea in patients with NAION who endorse symptoms of daytime sleepiness, have nighttime snoring, and/or are obese. Some studies suggest an association between NAION and obstructive sleep apnea. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Sleep apnea syndrome'.)

Orbital ultrasound may identify optic disc drusen in patients without other risk factors for ischemic optic neuropathy. (See "Nonarteritic anterior ischemic optic neuropathy: Epidemiology, pathogenesis, and etiologies", section on 'Ocular risk factors'.)

SUMMARY AND RECOMMENDATIONS — Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common cause of optic neuropathy in older adults.

The typical presentation is sudden onset of painless monocular vision loss, often upon awakening. (See 'Presenting symptoms' above.)

Examination findings include optic disc edema, reduced visual acuity (which is often mildly better than 20/60), and an afferent pupillary defect. (See 'Examination findings' above.)

A small optic cup is usually seen in the fellow eye and has been termed the "disc at risk." (See 'Optic disc appearance' above.)

In individuals older than 70 years, the major alternative diagnostic consideration is giant cell arteritis. Unlike NAION, arteritic ischemic optic neuropathy usually occurs in the setting of polymyalgia rheumatica. All patients over 70 years with ischemic optic neuropathy should have screening blood tests for giant cell arteritis, and further testing if these are abnormal or if the clinical setting is suspicious. (See 'Differential diagnosis' above and 'Diagnosis' above.)

In an older individual (>50 years) with typical clinical features of NAION, further testing beyond screening blood tests for giant cell arteritis is not required. (See 'Diagnosis' above.)

In young patients (<50 years), optic neuritis should be considered as an alternate diagnosis. Contrast-enhanced brain magnetic resonance imaging (MRI) study demonstrates optic nerve enhancement in most cases of optic neuritis, but very few patients with NAION. (See 'Differential diagnosis' above and 'Diagnosis' above.)

Patients with other atypical features of NAION should also undergo further testing. (See 'Diagnosis' above and "Optic neuropathies".)

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