eMedicine Specialties > Ophthalmology > Optic Nerve

Optic Neuropathy, Anterior Ischemic

Author: Brian R Younge, MD, Professor of Ophthalmology, Mayo Clinic School of Medicine
Contributor Information and Disclosures

Updated: Nov 26, 2007

Introduction

Background

Field defects typical of ischemic optic neuropathy were probably first described by Knapp in 1875. Miller and Smith first used the term ischemic optic neuropathy in 1966, and Hayreh later added the term anterior. In 1924, Uhthoff first described severe visual loss, with field defects and swollen optic discs.¹

Anterior ischemic optic neuropathy (AION) is the most common cause of acute optic neuropathy in older age groups. It can be nonarteritic (nonarteritic anterior ischemic optic neuropathy [NAION]) or arteritic, the latter being associated with giant cell arteritis. It is characterized by visual loss associated with optic disc swelling of a pallid nature, sometimes with flame hemorrhages on the swollen disc or nearby neuroretinal layer, and sometimes with nearby cotton-wool exudates. Visual loss is usually sudden, or over a few days at most, and it is usually permanent, with some recovery possibly occurring within the first weeks or months. Optic atrophy of varying degrees ensues within the next few weeks, and it is usually generalized but may be sectorial (NAION).

Although the pathophysiology differs in the arteritic form of AION, ischemia is the end result, as the results on vision are the same. According to Rucker, temporal arteritis probably was first described very early by Ali Ibn Isa (AD 940-1010).² In modern times (1890), Hutchinson described a disease of this nature, and, in 1932, Horton and colleagues at the Mayo Clinic used the term temporal arteritis.^3,4 To better describe the histologic features, Gilmour suggested the term giant cell arteritis in 1941. Treatment with steroids was started at the Mayo Clinic in 1949.

Pathophysiology

AION is thought to be an ischemic process affecting the posterior circulation of the globe, principally vessels (ie, short posterior ciliary arteries) supplying the optic nerve at its exit from the eye. Only glial cells support the optic disc at this site, and it is the only site in which swelling can occur. More posterior ischemia results in a similar condition, without visible swelling, and is termed posterior ischemic optic neuropathy. Early observations of optic disc photographs suggested that patients with small discs having smaller or nonexistent cups have an anatomical predisposition for NAION. As an ischemic episode evolves, the swelling compromises circulation, with a spiral of ischemia resulting in further neuronal damage. The ischemic spiral is less implicated in the arteritic type of AION, in which the entire ophthalmic arterial circulation to the eye and orbit may be compromised.

Frequency

United States

Patients with both arteritic and nonarteritic forms of AION are usually older than 50 years, with females predominating in the arteritic group. The incidence of the nonarteritic type is 2.3-10.3 per 100,000 in the United States, and, for the arteritic type, it is 0.36 per 100,000. In the arteritic group, incidence, like that of giant cell arteritis, increases almost exponentially with advanced age. The literature seems to support the notion that whites are affected more commonly than blacks in the nonarteritic group, and people of Scandinavian or European ancestry are the most commonly affected ethnic group in the arteritic type.

International

In the nonarteritic group, incidence is higher in whites and uncommon in other races.

The countries with the highest incidence of arteritic AION are the Scandinavian countries (ie, Norway, Denmark, Sweden), followed by Germany. The arteritic form is not as well recognized in non-whites. Recent genetic evidence may help to explain this incidence.

Mortality/Morbidity

NAION is not commonly associated with life-threatening conditions, although the presence of other vascular conditions is frequent (eg, hypertension, 46.9%; diabetes, 23.9%; myocardial infarction, 11%). The role of smoking in this disease is unclear. By contrast, the arteritic form of AION is associated with a more morbid condition, giant cell (cranial) arteritis. This condition affects many organs of the body, and the incidence of death associated with it is higher than that of the general population. Late-onset abdominal aortic aneurysms contribute to the morbidity and mortality of giant cell arteritis.

Bilateral visual loss is more common in the arteritic form of the disease, especially if treatment is delayed, and approximates 50% in some earlier series. By contrast, bilateral visual loss may be seen in 12-19% of NAION, and it usually occurs sequentially instead of simultaneously.

Progressive visual loss in the contralateral eye can occur in either form of AION, despite steroids, anticoagulation, or hyperbaric oxygen. Progressive visual loss is less common and usually stabilizes in a few days.

Race

NAION is most common in whites (95%); it is less common in African Americans (2%), Asians (3%), and Hispanics (1%). The arteritic form of the disease is predominantly described among whites of European descent, particularly Scandinavian and German.

It was a past misconception that African American patients did not succumb to giant cell arteritis. However, numerous documented cases of giant cell arteritis in blacks exist; giant cell arteritis in African American patients is not uncommon.

Sex

Females dominate the incidence in both forms of AION, but only slightly in the nonarteritic form (1.2:1), as compared to the arteritic type (2:1).

Age

Both disorders are found in older age groups. In the nonarteritic group, age ranges from the late 40s and older. The arteritic group almost always is older than 50 years, with an exponential increase with advanced age (90% of patients are >60 y). Rare cases of AION occur before 40 years, and the differentiation from optic neuritis associated with demyelinating disease is important in this crossover age group.

Clinical

History

• Visual loss is painless in at least 90% of patients with NAION. The vision loss is noticed upon awakening, perhaps due to nocturnal hypotension.
• Patients with arteritic AION often have symptoms other than visual loss, such as malaise, headache, scalp tenderness and tender temporal arteries, jaw pain on mastication (jaw claudication), generalized muscle aches, and swelling.
• The earlier manifestations of the disease include malaise, weight loss, fever, vague abdominal or GI pains, and anorexia.
• Late manifestations, often years later, include a much higher incidence of abdominal aortic aneurysm.

Physical

• Nonarteritic anterior ischemic optic neuropathy
  • NAION has typical findings of visual loss and field loss in an otherwise asymptomatic individual.
  • A small cup disc ratio is usually noted. Initially, the optic disc is swollen and pale, often in a generalized or diffuse manner.
  • Sectorial disc edema, especially of the superior disc, is classic.
  • Visual loss with NAION usually is not as severe as with arteritic AION, but vision loss as severe as no light perception has been described.
• Arteritic anterior ischemic optic neuropathy
  • In patients with arteritic AION, the disc is classically described as chalky white, pale, and swollen.
  • Ischemia in multiple vascular territories is not uncommon (eg, central retinal artery occlusion, choroidal infarction, anterior segment ischemia, extraocular muscle ischemia causing diplopia).
  • The temporal arteries may be quite prominent, ropey, and tender.
  • Oral, tongue, or even scalp ulcers rarely may be seen.

Causes

AION is an ischemic disease, but the cause is yet to be found definitively. In the nonarteritic form, atherosclerosis is assumed to be the basis, with its effect on the circulation of the optic nerve head. The posterior ciliary arteries feed the optic nerve head, and, despite variable results in animal primate models with ligation of the posterior ciliary arteries, their susceptibility to atherosclerosis and arteriosclerosis in a widespread manner seems to be the underlying cause. In the arteritic form, the basis for the ischemia is identical in pattern, with a giant cell arteritis involving most of the orbital vessels, including the central retinal artery, and the posterior ciliary arteries. Involvement of the branch retinal arterioles is rare presumably because of the lack of internal elastic lamina.

• Elucidating the genetic predisposition to giant cell arteritis has yet to be completed, but it has promise. Incidence in families of Scandinavian origin is high, and it may be possible to genetically determine those persons who are predisposed to this disorder. Human leukocyte antigen (HLA) haplotypes also may provide some interesting relationships, as there are very rare instances of giant cell arteritis in patients with true rheumatoid arthritis. The proximity of the gene locus in these 2 diseases seems to preclude the expression of both diseases in the same individual.
• According to Miller's edition of Walsh and Hoyt's Clinical Neuro-ophthalmology, the causes and associated conditions of AION are as follows⁵ :
  • Vasculitides
    • Giant cell arteritis
    • Polyarteritis nodosum
    • Systemic lupus
    • Buerger disease
    • Allergic vasculitis
    • Postviral vasculitis
    • Postimmunization
    • Syphilis
    • Radiation necrosis
  • Systemic vasculopathies
    • Hypertension
    • Atherosclerosis
    • Diabetes mellitus
    • Migraine
    • Takayasu disease
    • Carotid occlusive disease
  • Hematologic
    • Polycythemia vera
    • Sickle cell disease (trait)
    • Acute hypotension (shock)
    • Glucose-6-phosphate dehydrogenase deficiency (G-6-PD)
  • Ocular
    • Postcataract (possibly)
    • Low-tension glaucoma

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