Andrew G. Lee, MD

Clinical Features

Anterior ischemic optic neuropathy is a common cause of acute unilateral vision loss with optic disc edema. Unlike optic neuritis, anterior ischemic optic neuropathy is typically painless. Anterior ischemic optic neuropathy affects patients who are middle-aged to older adults (usually older than age 50) with underlying vasculopathic risk factors (e.g., hypertension, diabetes, high cholesterol, and smoking) (Table 1). Optic disc edema (anterior ischemic optic neuropathy) in the acute phase is required for the diagnosis of anterior ischemic optic neuropathy. Patients with ischemic optic neuropathy, however, may present without optic disc edema (posterior ischemic optic neuropathy). Elderly patients with posterior ischemic optic neuropathy should be evaluated for giant cell arteritis. Patients with postsurgical, posthypotensive ischemic optic neuropathy may have anterior ischemic optic neuropathy or posterior ischemic optic neuropathy.

Table 1. Typical Features of Non-arteritic Anterior Ischemic Optic Neuropathy

Age usually over 40 years
Vasculopathic risk factors (e.g., hypertension, diabetes, elevated cholesterol)
Unilateral loss of visual acuity and/or visual field
Ipsilateral relative afferent papillary defect
Visual field defects consistent with an optic neuropathy (e.g., central, cecocentral, arcuate, or altitudinal)
Optic disc edema (usually pallid edema) in the acute phase followed by optic atrophy that may be sector or diffuse
Small cup and cup to disc ratio

Evaluation

The major diagnostic consideration in anterior ischemic optic neuropathy is differentiating arteritic (e.g., giant cell arteritis) from non-arteritic ischemic optic neuropathy. Elderly patients with anterior ischemic optic neuropathy should be questioned regarding headache, scalp tenderness, and jaw claudication for giant cell arteritis. A serum erythryocyte sedimentation rate and/or C-reactive protein should be performed in patients suspected of having giant cell arteritis. Table 2 lists some of the conditions associated with ischemic optic neuropathy.

Table 2. Conditions Associated with Ischemic Optic Neuropathy

Vasculopathic (e.g., atherosclerosis, diabetes, elevated cholesterol, smoking)
Hypotension (e.g., post-surgical) or hypertension
Acute blood loss
Inflammatory (e.g., collagen vascular disorders, giant cell arteritis)
Hematologic disorders (e.g., anemia)
Infection (e.g., aspergillus, herpes zoster)
Internal carotid artery occlusion or dissection
Migraine
Radiation therapy
Optic disc drusen
Obstructive sleep apnea

Patients with non-arteritic ischemic optic neuropathy do not have other ocular or neurologic symptoms or signs. Transient visual loss does not typically occur in the non-arteritic form of anterior ischemic optic neuropathy and should prompt consideration for temporal arteritis. Neuroimaging is not indicated for typical non-arteritic ischemic optic neuropathy. Patients with atypical features may require further evaluation including neuroimaging for other etiologies for an optic neuropathy. Although vascular disease, hypercoaguable state, inflammatory disease, and emboli are rare causes of anterior ischemic optic neuropathy, typical cases do not require additional laboratory or radiographic evaluation.

Generally, carotid doppler studies and cardiac echocardiography are not indicated for non-arteritic ischemic optic neuropathy. Measurement of 24-hour blood pressure may identify individuals with nocturnal hypotension but limited treatment options are available for patients at risk. Orbital ultrasound may identify optic disc drusen in patients without other risk factors for ischemic optic neuropathy. Table 3 lists some atypical features for non-arteritic ischemic optic neuropathy that might prompt consideration for further work up.

Table 3. Atypical Features of Anterior Ischemic Optic Neuropathy

Age less than 40 years old
No vasculopathic risk factor
Large rather than small cup:disc ratio
Lack of optic disc edema at presentation (posterior ischemic optic neuropathy)
Hemianopic visual field loss
Bilateral simultaneous or rapidly sequential anterior ischemic optic neuropathy
Transient visual loss precedes visual loss (may be seen in the arteritic form)

Although the visual loss typically occurs at the same time as the optic disc edema, patients may present with asymptomatic or presymptomatic optic disc edema. Macular exudates or macular edema may occur in anterior ischemic optic neuropathy but are less common findings. After the resolution of the optic disc edema, sector or diffuse optic atrophy usually develops (Slide 1 and Slide 2).

Treatment

Slide 1

There is no proven effective therapy for non-arteritic ischemic optic neuropathy. Corticosteroid treatment should be instituted for patients suspected of having giant cell arteritis. Medical control of underlying vasculopathic risk factors (e.g., hypertension, diabetes, and smoking) is reasonable and some patients have occult disease. Over-aggressive control of systemic arterial hypertension may produce nocturnal hypotension and consideration should be given for taking blood pressure medications in the morning. Patients with acutely elevated hypertension should not have their blood pressure lowered too rapidly as this may precipitate non-arteritic ischemic optic neuropathy. Aspirin therapy may reduce the risk of non-arteritic ischemic optic neuropathy in the fellow eye but the evidence is limited and conflicting.

Johnson and colleagues reported a prospective, randomized, double-masked, placebo-controlled clinical trial. Twenty subjects with non-arteritic ischemic optic neuropathy of 30-months mean duration were randomized to low-dose levodopa and carbidopa or placebo for 3 weeks. At 12 weeks, the levodopa group was provided a higher, conventional dose of levodopa and carbidopa for 3 additional weeks. At 12 weeks, the levodopa group experienced a significant (P=.16) mean difference in improvement of visual acuity of 5.9 letters from the placebo group, and at 24 weeks the treatment effect remained (P=.36). There was a mean gain of 7.5 letters in the levodopa group compared to the placebo group, and three subjects experienced a doubling of the visual angle as denoted by a gain of at least 15 letters. No significant improvement was noted for visual field, which calls into question the reliability of the visual acuity improvement.

In a second follow-up study, Johnson and colleagues further studied the effect of levodopa on visual function in patients treated within 45 days of onset of non-arteritic ischemic optic neuropathy. In this non-randomized, retrospective study involving 37 patients, the researchers concluded that patients treated with levodopa within 45 days of onset of non-arteritic ischemic optic neuropathy were more likely to experience improvement and less likely to have worsened visual acuity than untreated patients.

Slide 2

Despite the above reports, there are no proven medical or surgical options in non-arteritic ischemic optic neuropathy. In a prospective, randomized trial, patients with non-arteritic ischemic optic neuropathy were randomly assigned to either surgery with optic nerve sheath fenestration in 119 patients or a control group of 125 patients. The primary outcome measure was a 3 or more line improvement of visual acuity after 6 months, and visual field mean deviation was a secondary outcome measure. After 6 months, 32.6% of the optic nerve sheath fenestration (surgery) group had improved 3 or more lines of visual acuity compared with 42.7% of the control group; but 23.9% of the optic nerve sheath fenestration group had lost 3 or more lines of visual acuity compared with only 12.4% of the control group. Likewise, visual field data confirmed a lack of benefit for surgery. The 3-month, 12-month, and 24-month data confirmed the findings of the 6-month data (Ischemic Optic Neuropathy Decompression Trial Research Group, 2000). In addition, no indication of benefit from optic nerve sheath fenestration was present in the subgroup of patients with progressive visual loss. The authors concluded that optic nerve sheath fenestration is not effective and may be harmful in non-arteritic ischemic optic neuropathy.

Prognosis

Most patients with non-arteritic ischemic optic neuropathy gain 1 or 2 lines of vision or remain unchanged after the acute loss of vision. Progressive visual loss occurs in a smaller percentage (15% to 20%) of patients with non-arteritic ischemic optic neuropathy. Recurrence of non-arteritic ischemic optic neuropathy in the same eye is uncommon but may involve the fellow eye in 12% of cases.

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