Anterior Ischemic Optic Neuropathy 

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 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 is usually generalized but may be sectorial (NAION).

Although the pathophysiology differs in the arteritic form of anterior ischemic optic neuropathy, 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.

Examples of anterior optic neuropathy are shown in the images below.

Anterior ischemic optic neuropathy 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 nonarteritic anterior ischemic optic neuropathy. 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 anterior ischemic optic neuropathy, 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 anterior ischemic optic neuropathy 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 anterior ischemic optic neuropathy are the Scandinavian countries (ie, Norway, Denmark, Sweden), followed by Germany. The arteritic form is not as well recognized in non-whites. 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 anterior ischemic optic neuropathy 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 nonarteritic anterior ischemic optic neuropathy, and it usually occurs sequentially instead of simultaneously.

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

Race

Nonarteritic anterior ischemic optic neuropathy is most common in whites (95%); it is less common in blacks (2%), Asians (3%), and Hispanics (1%). The arteritic form of the disease is predominantly described among whites of European descent, particularly Scandinavian and German.

A past misconception was that black patients did not succumb to giant cell arteritis. However, numerous documented cases of giant cell arteritis in blacks are noted; giant cell arteritis in black patients is not uncommon.

Sex

Females dominate the incidence in both forms of anterior ischemic optic neuropathy, but only slightly in the nonarteritic form (1.2:1) compared with 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 anterior ischemic optic neuropathy occur before 40 years, and the differentiation from optic neuritis associated with demyelinating disease is important in this crossover age group.