Arteritic Anterior Ischemic Optic Neuropathy (AAION)

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Arteritic Anterior Ischemic Optic Neuropathy (AAION)

Introduction

Acute and painless optic neuropathy that occurs predominantly in patients over 70 years old. Ischemia occurs at the head of the optic nerve in relation with structural crowding of the nerve fibers and reduction of the vascular supply impairing perfusion and producing optic disc edema.

Epidemiology and Pathogenesis

It accounts for 5-10% of anterior ischemic optic neuropathies (AION) and it’s caused by inflammatory and thrombotic involvement of the short posterior ciliary arteries (SPCA’s) with resultant optic nerve head infarction. Postmortem studies of acute AAION cases show optic disc edema with necrosis of the prelaminar, laminar and retrolaminar portions of the nerve and chronic inflammatory cells infiltration. Fluorescein angiographic data support the histopathological evidence of involvement of the SPCAs in AAION. extremely poor or absent filling of the choroid has been depicted as a characteristic of AAION.

Ocular Manifestations

Rapid onset of painless, unilateral visual loss manifested by decreased visual acuity that is tipically severe (<20/200 in over 60% of the patients), visual field (altitudinal field defect is the most common) or both. A relative afferente pupillary defect is common in unilateral neuropathies. Pallor of the optic disc, which may be severe, chalky-white is the hallmark of AAION, but it’s not uncommon to see hyperemic swelling. The disc most often is swollen diffusely, but a segment of more prominent involvement may be present with flame hemorrhages located adjacent to the disc, and the peripapillary retinal arterioles frequently are narrowed.

It may occur as an ocular manifestation of the vasculitis related to giant cell arteritis (GCA) in 5-10% of the cases. Systemic symptoms of GCA are usually present: headache (most common) and tenderness of the temporal arteries or scalp, jaw claudication (symptom most specific for the disorder), malaise, anorexia and weight loss, fever, joint and muscle pain, and ear pain. Choroidal ischemia may be associated with the optic neuropathy and produces peripapillary pallor and edema deep to the retina. The disc of the fellow eye is of normal diameter in AAION, as is the physiologic cup. Occult GCA without overt systemic symptoms may occur in up to 20% of patients with AAlON.

Diagnosis

Measuremente of the erythrocyte sedimentation rate (ESR) remains the standard of care, which usually elevates up too 70-120mm/min in GCA suggesting the diagnosis. Measurement of serum C reactive protein (CRP) may aid in diagnosis. It has been reported a 97% specificity for temporal arteritis in cases of AION in which both ESR and CRP were elevated. Confirmation of the diagnosis of temporal arteritis by superficial temporal artery biopsy is recommended in cases of AION with clinical suspicion of arteritis. Positive biopsy findings (intimal thickening, internal limiting lamina fragmentation, and chronic inflammatory infiltrate with giant cells) is confirmatory for GCA. A negative biopsy doesn’t rule out arteritis (both discontinuous arterial involvement (‘skip lesions’) and solely contralateral temporal artery inflammation may result in false-negative results) with recent reports showing a 3-5% false-negative error rate. Optic Coherence Tomography is useful in assesing sectoral disc edema, retinal nerve fiber layer thickness, as well as documenting the resolution to a normal or an atrophic optic disc.

Differential Diagnosis

The differential diagnosis o AION include: idiopathic optic neuritis, optic nerve inflammation related to syphilis or sarcoidosis, infiltrative optic neuropathies, anterior orbital lesions with optic nerve compression, and diabetic papillopathy.

Treatment

Early treatment is essential. High dose systemic corticosteroid are standard. Intravenous methylprednisolone at 1g/day for the first 3 days has been recommended for severe cases. Oral prednisone in the range of 60-100mg/day may be used initially and for follow up to intravenous pulse therapy. Treatment is usually continued at a high dose for a several months before beginning taper.

Course and Outcome

Without treatment, visual loss occurs in 54-95% of the patients typically within 4 months. With corticosteroid therapy, the rate of such loss is reduced to an estimated 13%. Visual recovery of the affected eye that has treatment is poor with a 15-34% improvement rate, which is higher with intravenous therapy. Worst visual acuity has been reported in 9-17% in spite of therapy.

Additional Resources

References

1. Arnold AC: Ischemic optic neuropathies. Ophthalmol Clin North Am 2001; 14: pp. 83-98

2. Johnson LN, and Arnold AC: Incidence of nonarteritic and arteritic anterior ischemic optic neuropathy: population-based study in the state of Missouri and Los Angeles County, California. J Neuroophthalmol 1994; 14: pp. 38-44

3. MacMichael IM, and Cullen JF: Pathology of ischaemic optic neuropathy. In Cant JS (eds): The optic nerve. Proceedings of the Second William MacKenzie Memorial Symposium. London: Henry Kimpton, 1972. pp. 108-116

4. Hayreh SS: Anterior ischemic optic neuropathy. V. Optic disc edema an early sign. Arch Ophthalmol 1981; 99: pp. 1030-1040

5. Hayreh SS, Podhajsky PA, and Zimmerman P: Ocular manifestations of giant cell arteritis. Am J Ophthalmol 1998; 125: pp. 509-520

6. Beck RW, Servais GE, and Hayreh SS: Anterior ischemic optic neuropathy. IX. Cup-to-disc ratio and its role in pathogenesis. Ophthalmology 1987; 94: pp. 1503-1508