Visually Evoked Response Tests For Optic Nerve Issues.

The Visually Evoked Response test, also known as the Visually Evoked Potential test, is a test used to determine if there is a disease that is removing the myelin sheath along the optic nerve.  Because damage to the sheath is often overlooked by the patient due to lack of symptoms, the visually evoked response test is credited with clarifying a number of diagnoses well in advance of symptoms that would have been noticed. 

There are a number of reasons that the myelin sheath along the nerve can be damaged.  Optic Neuritis or other demyelinating events like multiple sclerosis can cause trouble in the sheath without discernable symptoms.  Because of the Visually Evoked Response test can detect silent lesions and even episodes that have removed the sheath in the past, they are very useful diagnostic tools. A definite diagnosis of multiple sclerosis requires at least two distinct times that the myelin was removed or damaged in two different central nervous system sites which are separated by at least one month.  Even when other tests like MRI’s cannot, visually evoked potential tests can often provide evidence of such episodes.

The test is painless and basically consists of the patient being fitted with EEG sensors at separate spots on their head.  One eye is tested while the other has an eye patch on it. The patient then watches a lack and white checkered pattern on a TV screen in a darkened room. The black and white squares alternate on a regular cycle which generates electrical pulses along the optic nerve and into the brain.

Each time the pattern on the TV screen is reversed there is a transmission along the optic nerve all the way through the optic areas of the brain.  When the signal gets all the way to the end of the optic pathway, the time the signal took to get to the end is noted.  If the time is slower than normal (normal being about 100 milliseconds) then there is an issue along the optic pathway. 
The cause for a slowed time on the Visually Evoked Response test can be many things.  White matter lesions along the pathway, optic neuritis, MS or even a vitamin B12 deficiency can result in a slow time.  Finding out this information painlessly and quickly makes the visually evoked response test one of the most useful and accurate diagnostic tools available for optic path issues.