Anterior ischemic optic neuropathy
Encyclopedia
Anterior ischemic optic neuropathy (AION) is a medical condition involving loss of vision due to damage to the optic nerve
from insufficient blood supply. AION is generally divided into two types: arteritic AION (or AAION) and non-arteritic AION (NAION or simply AION). This article will focus primarily on non-arteritic AION.
(also called giant cell arteritis
), an inflammatory disease of medium-sized blood vessels (Chapel-Hill-Conference) that occurs especially with advancing age. In contrast, NAION results from the coincidence of cardiovascular risk factors in a patient with "crowded" optic discs. Non-arteritic AION is more common than AAION and usually occurs in a slightly younger group than AAION. While only a few cases of NAION result in near total loss of vision, most cases of AAION involve nearly complete vision loss.
Beyond this introduction, this article will focus on non-arteritic AION. For a discussion on arteritic AION see the separate article arteritic anterior ischemic optic neuropathy
. Though the term "AION" can be used to describe either anterior ischemic optic neuropathy in general or non-arteritic AION specifically, in this article "NAION" henceforth will be used to refer to non-arteritic anterior ischemic optic neuropathy. Nonarteritic anterior ischemic optic neuropathy (NAION) is an isolated white-matter stroke of the optic nerve (ON). NAION is the most common cause of sudden optic nerve-related vision loss, affecting more than 10,000 Americans every year, often bilaterally. No clinically effective treatments exist, largely because little is known about its pathophysiology, and there are few histopathological studies of the acute condition.
An exhaustive review article published in March 2009 described the latest information on arteritic and non-arteritic ischemic optic neuropathy, both anterior (A-AION and NA-AION) and posterior (A-PION, NA-PION, and surgical).
Since arteritic AION is similar in presentation to non-arteritic AION, patients over the age of 50 diagnosed with NAION must be evaluated to exclude AAION (symptoms: painful jaw muscle spasms, scalp tenderness, unintentional weight loss, fatigue, myalgias and loss of appetite). Furthermore, NAION patients over the age of 75 should often be blood tested regardless.
shape. The optic disc is where the axons from the retinal ganglion cells collect into the optic nerve. The optic nerve is the bundle of axons that carry the visual signals from the eye to the brain. This optic nerve must penetrate through the wall of the eye, and the hole to accommodate this is usually 20-30% larger than the nerve diameter. In some patients the optic nerve is nearly as large as the opening in the back of the eye, and the optic disc appears "crowded" when seen by ophthalmoscopy
. A crowded disc is also referred to as a "disc at risk". While a risk factor, the vast majority of individuals with crowded discs do not experience NAION.
The second major risk factor involves more general cardiovascular risk factors. The most common are diabetes
, hypertension
and high cholesterol
levels. While these factors predispose a patient to develop NAION, the most common precipitating factor is marked fall of blood pressure during sleep (nocturnal arterial hypotension)- that is why at least 75% of the patients first discover visual loss first on waking from sleep. These vascular risk factors lead to ischemia (poor blood supply) to a portion of the optic disc. The disc then swells, and in a crowded optic disc, this leads to to compression and more ischemia.
Since both eyes tend to have a similar shape, the optometrist or ophthalmologist will look at the good eye to assess the anatomical predisposition. The unaffected eye has a 14.7% risk of NAION within five years.
A number of studies have linked Viagra use with NAION.
There is much research currently underway looking at ways to protect the nerve (neuroprotection) or even regenerate new fibers within the optic nerve. There are no current clinical trials for the treatment of NAION. So far we have no evidence that the so-called neuroprotectors have any beneficial effect in NAION.
In addition to such research, patents have been applied for by Pfizer, The University of Southern California, Otsuka Pharmaceutical and other individual inventors for innovations related to the treatment of anterior ischemic optic neuropathy.
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
from insufficient blood supply. AION is generally divided into two types: arteritic AION (or AAION) and non-arteritic AION (NAION or simply AION). This article will focus primarily on non-arteritic AION.
Introduction
The distinction between AAION and NAION was made to highlight the different etiologies of anterior ischemic optic neuropathy. AAION is due to temporal arteritisTemporal arteritis
Giant-cell arteritis or Horton disease is an inflammatory disease of blood vessels most commonly involving large and medium arteries of the head...
(also called giant cell arteritis
Arteritis
Arteritis is inflammation of the walls of arteries, usually as a result of infection or auto-immune response.-Types:Some disorders have arteritis as their main feature...
), an inflammatory disease of medium-sized blood vessels (Chapel-Hill-Conference) that occurs especially with advancing age. In contrast, NAION results from the coincidence of cardiovascular risk factors in a patient with "crowded" optic discs. Non-arteritic AION is more common than AAION and usually occurs in a slightly younger group than AAION. While only a few cases of NAION result in near total loss of vision, most cases of AAION involve nearly complete vision loss.
Beyond this introduction, this article will focus on non-arteritic AION. For a discussion on arteritic AION see the separate article arteritic anterior ischemic optic neuropathy
Arteritic anterior ischemic optic neuropathy
Arteritic anterior ischemic optic neuropathy is the cause of vision loss that occurs in temporal arteritis . Temporal arteritis is an inflammatory disease of medium-sized blood vessels that happens especially with advancing age. AAION occurs in about 15-20 percent of patients with temporal arteritis...
. Though the term "AION" can be used to describe either anterior ischemic optic neuropathy in general or non-arteritic AION specifically, in this article "NAION" henceforth will be used to refer to non-arteritic anterior ischemic optic neuropathy. Nonarteritic anterior ischemic optic neuropathy (NAION) is an isolated white-matter stroke of the optic nerve (ON). NAION is the most common cause of sudden optic nerve-related vision loss, affecting more than 10,000 Americans every year, often bilaterally. No clinically effective treatments exist, largely because little is known about its pathophysiology, and there are few histopathological studies of the acute condition.
An exhaustive review article published in March 2009 described the latest information on arteritic and non-arteritic ischemic optic neuropathy, both anterior (A-AION and NA-AION) and posterior (A-PION, NA-PION, and surgical).
Symptoms and diagnosis
NAION typically presents suddenly and upon awakening. The patient notes seeing poorly in one eye. Vision in that eye is obscured by a dark shadow, often involving just the upper or lower half of vision, usually the area towards the nose. There is no pain. In approximately 6 months following the infarct visual acuity improves by 3 or more lines of vision on the Snellen Chart(the chart with smaller letters on each lower line) in 42.7% of patients.In addition, vision had worsened by 3 lines or more in 12.4% of patients. Second eye involvement occurs in approximately 15% to 20% of patients with NAION within 5 years. Fortunately, it may not be terribly devastating as the visual acuity may remain only moderately impaired. Furthermore, most cases of NAION involve the loss of a hemifield (either the upper or lower half of the visual field, but not both). A few cases of NAION involve almost total loss of vision.Since arteritic AION is similar in presentation to non-arteritic AION, patients over the age of 50 diagnosed with NAION must be evaluated to exclude AAION (symptoms: painful jaw muscle spasms, scalp tenderness, unintentional weight loss, fatigue, myalgias and loss of appetite). Furthermore, NAION patients over the age of 75 should often be blood tested regardless.
Causes and risk factors
The mechanism of injury for NAION used to be quite controversial. However, the experts in the field (neuro-ophthalmologists) have come to a consensus that most cases involve two main risk factors. The first is a predisposition in the form of a type of optic discOptic disc
The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive rods or cones to respond to a light stimulus at this point. This causes a break in the visual field called "the blind spot" or the "physiological blind spot"...
shape. The optic disc is where the axons from the retinal ganglion cells collect into the optic nerve. The optic nerve is the bundle of axons that carry the visual signals from the eye to the brain. This optic nerve must penetrate through the wall of the eye, and the hole to accommodate this is usually 20-30% larger than the nerve diameter. In some patients the optic nerve is nearly as large as the opening in the back of the eye, and the optic disc appears "crowded" when seen by ophthalmoscopy
Ophthalmoscopy
Ophthalmoscopy is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope . It is done as part of an eye examination and may be done as part of a routine physical examination...
. A crowded disc is also referred to as a "disc at risk". While a risk factor, the vast majority of individuals with crowded discs do not experience NAION.
The second major risk factor involves more general cardiovascular risk factors. The most common are diabetes
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
, hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
and high cholesterol
Cholesterol
Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
levels. While these factors predispose a patient to develop NAION, the most common precipitating factor is marked fall of blood pressure during sleep (nocturnal arterial hypotension)- that is why at least 75% of the patients first discover visual loss first on waking from sleep. These vascular risk factors lead to ischemia (poor blood supply) to a portion of the optic disc. The disc then swells, and in a crowded optic disc, this leads to to compression and more ischemia.
Since both eyes tend to have a similar shape, the optometrist or ophthalmologist will look at the good eye to assess the anatomical predisposition. The unaffected eye has a 14.7% risk of NAION within five years.
A number of studies have linked Viagra use with NAION.
Treatment
Once NAION happens, it was thought that there was no accepted treatment to reverse the damage. However, a recent large study has shown that if patients are treated with large doses of corticosteroid therapy during the early stages of NAION, in eyes with initial visual acuity of 20/70 or worse, seen within 2 weeks of onset, there was visual acuity improvement in 70% in the treated group compared to 41% in the untreated group (odds ratio of improvement: 3.39; 95% CI:1.62, 7.11; p ¼ 0.001) (Graefes Arch. Clin. Exp. Ophthalmol 2008;246,:1029–1046.). That study and a natural history study on NAION (Ophthalmology 2008;115: 298–305.) showed that visual acuity can improve up to 6 months and not after that. To minimize the risk of further visual loss in the fellow eye or the same eye, it is essential to reduce the risk factors. Common sense dictates trying to control the cardiovascular risk factors for many reasons, including protection from this happening to the second eye. Sudden vision loss should lead to an ophthalmological consultation. If NAION is suspected, then ideally a neuro-ophthalmologist's consultation should be obtained.There is much research currently underway looking at ways to protect the nerve (neuroprotection) or even regenerate new fibers within the optic nerve. There are no current clinical trials for the treatment of NAION. So far we have no evidence that the so-called neuroprotectors have any beneficial effect in NAION.
In addition to such research, patents have been applied for by Pfizer, The University of Southern California, Otsuka Pharmaceutical and other individual inventors for innovations related to the treatment of anterior ischemic optic neuropathy.
External links
- Online handbook of Ocular Disease Management at revoptom.com
- Department of Ophthalmology & Visual Sciences at University of IowaUniversity of IowaThe University of Iowa is a public state-supported research university located in Iowa City, Iowa, United States. It is the oldest public university in the state. The university is organized into eleven colleges granting undergraduate, graduate, and professional degrees...
- Polymyalgia rheumatica article from National Institute of Arthritis and Musculoskeletal and Skin DiseasesNational Institute of Arthritis and Musculoskeletal and Skin DiseasesThe National Institute of Arthritis and Musculoskeletal and Skin Diseases, or NIAMS, is an institute of the National Institutes of Health, an agency of the United States Department of Health and Human Services...