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PubMed This is a summary of 26 peer-reviewed journal articles Updated
Ophthalmology

Testing & Finding the Answer

At a Glance

AAION is a vision-threatening emergency often linked to giant cell arteritis. Doctors combine symptoms with inflammation blood tests, temporal artery biopsy, and ultrasound; normal results do not always rule it out, and suspected cases need prompt steroids.

When doctors suspect Arteritic Anterior Ischemic Optic Neuropathy (AAION), they begin an urgent series of tests to confirm the diagnosis and protect your vision [1][2]. Because this is a medical emergency, the most important rule of the diagnostic workup is that treatment must never be delayed for testing [3][4]. If your doctor strongly suspects Giant Cell Arteritis (GCA), they will likely start high-dose steroids first and then perform the tests to confirm the diagnosis [5][6].

The “Big Three” Blood Tests

Blood work is often the first step in checking for the widespread inflammation associated with GCA [7]. Doctors look at three specific markers:

  • ESR (Erythrocyte Sedimentation Rate): Measures how quickly red blood cells sink to the bottom of a tube; faster sinking indicates more inflammation [8].
  • CRP (C-reactive Protein): A protein produced by the liver that rises sharply when there is inflammation in the body [8].
  • Platelet Count: Platelets are blood-clotting cells that often increase in number when the body is fighting significant inflammation [8][9].

While these tests are very helpful, they are not perfect. In about 3% of patients with biopsy-proven GCA, all three of these tests will come back completely normal [10][8]. Therefore, a normal blood test cannot “rule out” the condition if your symptoms strongly suggest it [11][12].

Temporal Artery Biopsy (TAB): An Important Test

A temporal artery biopsy is currently an important established way to confirm GCA [13]. In this minor surgical procedure, typically done under local anesthesia, a surgeon makes a small incision in the skin near your temple and removes a short segment of the temporal artery to be examined under a microscope [14]. You may experience some local bruising or mild tenderness afterward.

To ensure the test is accurate, doctors follow two critical guidelines:

  1. Specimen Length: The surgeon should remove a piece of the artery that is often 1 to 2 centimeters long, depending on local protocols [15]. This is because the inflammation in GCA is often patchy, with healthy sections of the artery alternating with diseased ones (known as skip lesions) [16][13]. A longer sample reduces the chance of accidentally taking only a healthy section [15].
  2. Timing: The biopsy should ideally be performed within 1 to 2 weeks of starting steroid treatment [3][5]. While steroids can eventually “clear” the signs of inflammation from the artery, the evidence of GCA usually remains visible for several weeks [17][18].

Temporal Artery Ultrasound and the “Halo Sign”

Many medical centers now use specialized Color Doppler Ultrasound as an initial test [19]. This non-invasive scan looks for the halo sign—a dark, ring-like swelling around the wall of the artery caused by inflammation [20][21].

If an experienced specialist finds a clear halo sign, it strongly supports a GCA diagnosis [20]. However, if the ultrasound is normal but the doctor still suspects GCA, neither a negative biopsy nor a negative scan automatically excludes GCA when clinical suspicion remains high, as the ultrasound can sometimes miss the inflammation [22][12].

Distinguishing AAION from NAION

Your doctors must also determine if your vision loss is “Arteritic” (AAION) or “Non-Arteritic” (NAION). While both involve a lack of blood flow to the optic nerve, they have very different causes and treatments [1].

Feature Usual Pattern in AAION Usual Pattern in NAION
Cause Inflammation of the arteries (GCA) [23] Factors like high blood pressure or sleep apnea [24]
Vision Loss Often profound and severe [25] Usually less severe; often affects half the field of vision [26]
Optic Disc Often appears “chalky white” or very pale [25] Usually appears swollen and pink/red [26]
Other Symptoms Headache, jaw pain, fever, or fatigue [7] Usually no other body-wide symptoms [1]

In some tricky cases, AAION can “mimic” the appearance of NAION, so sudden vision loss always requires urgent attention [22][12].

Common questions in this guide

What tests are used to diagnose AAION?
Doctors usually check ESR and CRP blood tests, along with the platelet count, to look for inflammation linked to giant cell arteritis. They may also use a temporal artery ultrasound and a temporal artery biopsy while considering the pattern and severity of vision loss.
Can normal blood tests rule out giant cell arteritis in AAION?
No. A small percentage of people with biopsy-confirmed giant cell arteritis have normal ESR, CRP, and platelet results, so doctors must weigh the laboratory findings alongside symptoms and eye findings.
How soon after starting steroids should a temporal artery biopsy be done?
Ideally, the biopsy is performed within one to two weeks after steroids begin. Steroids can eventually reduce visible inflammation, but signs often remain in the artery for several weeks, so testing should not delay urgent treatment.
What does the halo sign on a temporal artery ultrasound mean?
The halo sign is a dark, ring-like swelling around the artery wall that suggests inflammation from giant cell arteritis. A clear sign supports the diagnosis, but a normal ultrasound does not always exclude it when symptoms keep suspicion high.
How do doctors tell AAION from NAION?
AAION often causes more profound vision loss, a very pale or chalky-white optic disc, and symptoms such as headache, jaw pain, fever, or fatigue. NAION is often less severe, with a swollen pink or red optic disc and no body-wide symptoms, although the patterns can overlap.
What happens during a temporal artery biopsy?
A surgeon usually uses local anesthesia, makes a small incision near the temple, and removes a short segment of the temporal artery for microscopic examination. Mild bruising or tenderness can occur afterward, and a longer sample may reduce the chance of missing patchy inflammation.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Were my blood samples for ESR and CRP taken before or after I started steroids?
  2. 2.Given that inflammatory markers can sometimes be normal in people with GCA, how are you weighing my lab results against my symptoms?
  3. 3.When is my temporal artery biopsy scheduled, and will the surgeon be taking a sample large enough to reduce false negatives?
  4. 4.If my initial ultrasound or biopsy is negative but my symptoms persist, what is the 'Plan B' for confirming my diagnosis?
  5. 5.Are you also checking my axillary (armpit) arteries during the ultrasound to increase the accuracy of the test?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (26)
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    Arteritic anterior ischaemic optic neuropathy: An update.

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    European journal of ophthalmology 2021; (31(6)):2818-2827 doi:10.1177/11206721211009447.

    PMID: 33892603
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    Orbital magnetic resonance imaging of giant cell arteritis with ocular manifestations: a systematic review and individual participant data meta-analysis.

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    European radiology 2023; (33(11)):7913-7922 doi:10.1007/s00330-023-09770-2.

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    Biopsy vs imaging in the diagnosis of giant cell arteritis. Viewpoint 1: in favour of imaging.

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    Orbital MRI Findings in a Patient With Giant Cell Arteritis (GCA): A Case Report.

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    Biopsy vs imaging for the diagnosis of giant cell arteritis. Viewpoint 2: in favour of biopsy.

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This page explains AAION and giant cell arteritis testing for informational purposes only and does not constitute medical advice. Sudden vision loss requires urgent medical evaluation.

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