Diagnosis

You're likely to see an ophthalmologist for a diagnosis, which is generally based on your medical history and an exam. The ophthalmologist likely will perform the following eye tests:

• A routine eye exam. Your eye doctor will check your vision and your ability to perceive colors and measure your side (peripheral) vision.
• Ophthalmoscopy. During this examination, your doctor shines a bright light into your eye and examines the structures at the back of your eye. This eye test evaluates the optic disk, where the optic nerve enters the retina in your eye. The optic disk becomes swollen in about one-third of people with optic neuritis.
• Pupillary light reaction test. Your doctor may move a flashlight in front of your eyes to see how your pupils respond when they're exposed to bright light. If you have optic neuritis, your pupils won't constrict as much as pupils in healthy eyes would when exposed to light.

Other tests to diagnose optic neuritis might include:

• Magnetic resonance imaging (MRI). An MRI scan uses a magnetic field and pulses of radio wave energy to make pictures of your body. During an MRI to check for optic neuritis, you might receive an injection of a contrast solution to make the optic nerve and other parts of your brain more visible on the images.

  An MRI is important to determine whether there are damaged areas (lesions) in your brain. Such lesions indicate a high risk of developing multiple sclerosis. An MRI can also rule out other causes of visual loss, such as a tumor.

• Blood tests. A blood test is available to check for infections or specific antibodies. Neuromyelitis optica is linked to an antibody that causes severe optic neuritis. People with severe optic neuritis may undergo this test to determine whether they're likely to develop neuromyelitis optica. For atypical cases of optic neuritis, blood may also be tested for MOG antibodies.
• Optical coherence tomography (OCT). This test measures the thickness of the eye's retinal nerve fiber layer, which is often thinner from optic neuritis.
• Visual field test. This test measures the peripheral vision of each eye to determine if there is any vision loss. Optic neuritis can cause any pattern of visual field loss.
• Visual evoked response. During this test, you sit before a screen on which an alternating checkerboard pattern is displayed. Attached to your head are wires with small patches to record your brain's responses to what you see on the screen. This type of test tells your doctor if the electrical signals to your brain are slower than normal as a result of optic nerve damage.

Your doctor is likely to ask you to return for follow-up exams two to four weeks after your symptoms begin to confirm the diagnosis of optic neuritis.