CLINICAL

  POSTERIOR

ASSESSING FOR AION

DIFFERENTIATING BETWEEN THE TWO FORMS CAN SAVE A PATIENT’S LIFE

A 75-YEAR-OLD Black male presented complaining of a painless acute decrease in vision OS. He denied any symptoms of scalp tenderness, jaw pain from chewing, or weight loss, which are specific for giant cell arteritis (GCA).

His medical history was significant for hypertension, Type 2 diabetes and hypercholesterolemia.

The patient’s BCVA was 20/25 OD and 20/50 OS. Examination revealed a relative afferent pupillary defect (RAPD) OS. Dilated exam showed optic nerve edema with a peripapillary hemorrhage OS. Humphrey visual field 24-2 testing revealed an inferior defect OS.

Medical testing showed normal inflammatory mediators, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).

Was this patient diagnosed with anterior arteritic ischemic optic neuropathy (AAION) or nonarteritic anterior ischemic optic neuropathy (NAION)?

Here, I discuss the etiology, symptoms, clinical signs and management options of both forms of AION, to help you figure it out.

ETIOLOGY

AION is believed to result from an ischemic process affecting the short posterior ciliary arteries, which supply the anterior portion of the optic nerve.

The condition is due to:

• Vasculitides (GCA or temporal arteritis, polyarteritis nodosa, systemic lupus erythematous, post-viral vasculitis and syphilis)

• Systemic vasculopathies (hypertension, atherosclerosis, diabetes mellitus, migraine and carotid occlusive disease)

• Hematologic conditions (polycythemia vera and sickle cell disease)

• Ocular conditions (cataract extraction, small/crowded optic nerve head with small physiological cup “disc at risk,” optic nerve head drusen, papilledema and glaucoma)

• Medications (erectile dysfunction drugs, interferon medications and amiodarone)

AION is a leading cause of acute profound vision loss in elderly patients, typically age 50 and older, and falls under two types: AAION, an autoimmune disorder, and NAION, a small vessel disease. AAION is more prevalent in white females, while NAION affects males and females nearly equally.

AAION is a life-threatening ocular emergency, most often due to GCA or temporal arteritis. Patients are at risk for not only blindness if immediate treatment is not rendered, but also systemic and neurological complications, such as myocardial infarction, stroke or seizures, all of which can potentially lead to death.

NAION is the most common form of AION and is not life threatening. A patient is susceptible to developing NAION if he or she has a vascular disease, such as hypertension, diabetes or hypercholesterolemia. Other predisposing factors are sleep apnea syndrome related to obesity, nocturnal arterial hypotension, elevated homocysteine or low vitamin B6 levels, smoking and glaucoma.

SYMPTOMS

AION patients may experience a number of prodromal signs and symptoms that occur one to two weeks prior to an acute attack. Several are “red flags” for AAION:

• Tenderness of the temporal arteries or scalp (red flag)

• Malaise (red flag)

• Loss of appetite (red flag)

• Loss of weight (red flag)

• Prominent, tender temporal arteries (red flag)

• Jaw claudication (red flag)

• Generalized muscle aches and swelling (red flag)

• Joint aches or pains

• Ear pain

• Sudden loss of vision (painless in NAION)

• Headaches

• Transient visual obscuration/amaurosis fugax

• Photopsia

AION is a leading cause of acute, profound vision loss in elderly patients, typically age 50 and older and falls under two types: AAION, an autoimmune disorder, and NAION, a small vessel disease. In these images of a patient diagnosed with NAION, note the optic nerve head edema and peripapillary flame-shaped hemorrhages.
Courtesy of Joseph Pizzimenti, O.D., F.A.A.O.

CLINICAL SIGNS

Clinical findings vary between the two AION presentations.

• Loss of visual acuity (more severe in AAION — <20/200 in more than 60% of patients vs. NAION — VA range from 20/20 to no light perception)

• Hemorrhages (more common in NAION vs. AAION)

• RAPD

• Loss of color vision

• Visual field defects (altitudinal hemianopsia, inferior visual field defect more common, arcuate and central scotomas)

• Optic nerve head edema

• Peripapillary flame-shaped hemorrhages

• Narrowed peripapillary retinal arterioles

• Cotton wool spots

• Diffuse or segmental disc pallor (severe pallor, chalky-white is the hallmark of AAION)

DIAGNOSIS/MANAGEMENT

To diagnose either form, use retinal photography to document, monitor and educate patients about their condition. In addition, employ visual field testing to look for altitudinal hemianopsia, arcuate and central scotomas. Also, use fluorescein angiography, which will reveal NAION’s normal choroidal filling or AAION’s poor choroidal circulation, the latter of which is due to posterior ciliary artery occlusion. Further, employ OCT to detect and monitor optic disc edema and retinal nerve fiber changes.

It is important to assess whether the patient is a current or former smoker, his or her medical history and what medications the patient takes, particularly when NAION is suspected. Also, take the patient’s blood pressure, and order laboratory testing for diabetes, hematological disorders and a lipid panel.

If you suspect AAION, order ESR and CRP testing to rule out GCA. Markedly elevated ESR and CRP are diagnostic of AAION. A temporal artery biopsy is the definitive diagnosis for GCA. Patients should have it performed immediately, however, therapy should be initiated while waiting for the results, as every minute counts in preventing irreversible vision loss. A temporal artery biopsy should also be performed once therapy has started (see below) to determine whether treatment is working. The American College of Rheumatologists recommends five criteria for the diagnosis of GCA: (1) 50 years of age or older at onset; (2) new onset of localized headache; (3) temporal artery pulse; (4) elevated ESR and (5) positive temporal artery biopsy.

Neuroimaging should be obtained in cases with significant pain, especially pain upon eye movement, to rule-out other causes, such as optic neuritis from multiple sclerosis. It is also recommended for those with an atypical course, including prolonged optic disc edema and/or recurrent visual loss, to exclude a mass lesion on the brain.

In patients with AAION, management is aimed at treating GCA. High-dose oral or intravenous steroids should be administered immediately to prevent further systemic, neurological and ocular complications and involvement of the other eye. Untreated, patients risk blindness in one or both eyes, with at least 50% of patients going blind in the other eye in 5 to 10 days, says the Indian Journal of Ophthalmology. Therapeutic intervention is also important, as GCA patients have a five-year risk of death from the condition, says The Journals of Gerontology Series “Biological Sciences and Medical Sciences.”

Management includes close monitoring and co-management with the treating physician. Treatment may be continued for several months with slow taper and in some cases, for years based on recurrence and severity of the disease.

The visual prognosis for AAION is poor, however, up to 15% of patients may experience improvement, according to Ophthalmology.

The visual prognosis is better for patients who have NAION, although some patients may experience decreased vision through the first few days or week of onset. There is no accepted therapy for NAION, and some patients, approximately 40%, may experience spontaneous recovery without treatment, says Ophthalmology. A number of medical options, including systemic steroids, aspirin therapy, intravitreal steroids and anti-vascular endothelial growth factor agents have been advocated. Surgical intervention for NAION is also not beneficial, according to the Ischemic Optic Neuropathy Decompression Trial. Systemic and intravitreal steroids have been found to improve visual outcome in the early phase of NAION, but studies have been inconclusive. Management of NAION is aimed at identifying and treating the underlying cause and, more importantly, ruling-out AAION.

THE ANSWER

So, what was the aforementioned patient diagnosed with? If you diagnosed him with NAION, you are correct! The patient was treated with steroids and closely monitored.

He later developed optic atrophy OS as a result of his condition. Although his vision loss and visual field defect is permanent, it remains stable. He is aware of the possibility of recurrence and continues to comply with his systemic disease management and follow-up care.

AION remains a diagnostic challenge for clinicians and a devastating condition for patients. As a result, it is crucial to distinguish AAION and NAION to prevent profound vision loss and life-threatening complications. Consequently, it is imperative to be aware of the clinical presentation and visual outcome of both conditions, so that timely and urgent treatment is administered. OM

SHERROL A. REYNOLDS, O.D., F.A.A.O., is an associate professor at the Nova Southeastern University College of Optometry and clinical preceptor/attending in the college’s diabetes and macular clinic. She is a fellow of the Optometric Retina Society and chairperson for the Florida Optometric Association Healthy Eyes Healthy People Committee. Comment at tinyurl.com/OMcomment.