How is optic neuritis (ON) diagnosed?
The diagnosis of ON is based on the patient's medical history, as well as the absence of other diseases which can cause visual loss. The ophthalmologic exam may help in showing abnormalities at the back of the eye in the optic disc, which is the part of the optic nerve visible using an instrument called an ophthalmoscope. There may be abnormalities of visual field testing, color vision, testing, and visual acuity testing that aid in the diagnosis.
Occasionally, other diseases have to be considered in diagnosing ON, but these are usually apparent during the history and examination. For example, some people who are older than 50 experience a sudden loss of vision in one eye which is due to a problem with blood flow to the eye, and not due to inflammation.
Is there any testing for optic neuritis?
Testing helps to exclude other diagnoses and evaluates the likelihood of other diseases. A magnetic resonance imaging (MRI) study of the brain and orbits (the eye sockets) with gadolinium contrast may confirm the diagnosis of acute demyelinating optic neuritis. In addition, patients whose MRI scans show two or more areas of demyelination in the brain are now known to have a higher risk of going on to develop MS than patients with few or no such areas.
MRI scans let doctors look at the brain and spinal cord by way of a very powerful magnet that shows inner tissues. Gadolinium helps to indicate inflammation in the brain and optic nerve. Gadolinium should not be used in patients with significant kidney disease or known allergic reactions to dyes used in contrast material.
Lumbar puncture is usually not necessary for isolated optic neuritis, but is sometimes used in assisting with the diagnosis of multiple sclerosis. If there are unusual features of the ON-for example, patient age of less than 15 years, bilateral ON, or symptoms suggesting infection-lumbar puncture may be needed to check for other diseases.
Blood tests may be necessary in some people with optic neuritis depending on the situation. Diseases which can be checked with a blood test include, but are not limited to, lupus erythematosus, temporal arteritis, sarcoidosis, syphilis, and Lyme disease.
The visual evoked potentials test is non-invasive and measures how electricity is conducted along visual pathways. The test calls for the patient to watch a checkerboard pattern on a screen while electrodes monitor brain activity. With ON, there may be slowing in one or both optic nerves.
Ocular coherence tomography is a new non-invasive technique to evaluate the back of the eye. The test can measure the nerve fiber layer at the back of the eye. Ocular coherence tomography's role in diagnosis ON is still unclear.