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. Pupils in eyes affected by optic neuritis don't constrict as much as those in healthy eyes do when stimulated by light.
Other tests to diagnose optic neuritis might include:
Magnetic resonance imaging (MRI) scan. 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 antibodies for neuromyelitis optica. People with severe optic neuritis may undergo this test to determine whether they're likely to develop neuromyelitis optica.
- Optical coherence tomography (OCT). This measures the thickness of the retinal nerve fiber layer, which is often thinner from optic neuritis.
- 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 the visual stimuli. This type of test detects the slowing of electrical conduction resulting from damage to the optic nerve.
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.