VISUAL EVOKED POTENTIAL RANGE

[Waydwnsouth1]

This will be short and sweet. Does anyone happen to know what the normal range is for the VEP test is?

[jreagan70]

It's a short question, but it doesn't have a short answer.

The VEP actually consists of several different tests, each with its own set of measurements. The test that's of interest in MS is latency, or speed of signal transmission from the retina to the visual cortex at the base of the skull.

In the purest academic sense, the latency cutoff is 110 msec. Because of "reality" factors, the cutoff that appears frequently in medical literature as being frequently used is 112 msec. That may be because results depend somewhat on the equipment that was used. give faster results than Dimmer, slower CRT monitors give slower results than brighter, faster LED monitors, and that often isn't accounted for in test reports. There are variations in individual pieces of equipment, and the "norms" for individual equipment often isn't accounted for.

Another thing that's not usually accounted for are patients' individual variations. Bodies go through cycles of higher and lower temperature, higher and lower blood pressure, higher and lower eye pressure, higher and lower hydration, and more. Without a doubt, they all have small, various effects on body systems. There's even a study of VEPs done on women relative to their menstrual cycles that showed significantly abnormal signal slowing during their periods. So an absolute cutoff of 110 ms as proof of normal latency and a healthy visual pathway, and a slower latency always indicating pathology, isn't always considered to be realistic.

All of the nuances also allow for differences in doctors' skill level in interpreting VEP results, which can lead to opposite interpretations and different diagnoses.

A VEP is also nonspecific. It can provide supporting information, but it isn't diagnostic by itself.

[Waydwnsouth1]

jreagan70,
Thank you for your reply. 110 is what I thought it was but I wasn't sure. When I gave my old Neuro my VEP results and told him the Neuro that ordered the test said my results were normal he disagreed. My results were 111 in both eyes. My old Neuro said it showed I had ON in both eyes but I don't know. If I did it couldn't have been bad.

[Poppy7402]

I've had two normal VEPs so far and been told that I've never had ON. However, a couple of weeks ago I had OCT done. This has shown macular thinning in both eyes so even though they say no ON, my eyes have been affected.

If you're worried about your eyes, then perhaps OCT could be something to look at?

[Jaidesmom]

jreagan70,
Thank you for your reply. 110 is what I thought it was but I wasn't sure. When I gave my old Neuro my VEP results and told him the Neuro that ordered the test said my results were normal he disagreed. My results were 111 in both eyes. My old Neuro said it showed I had ON in both eyes but I don't know. If I did it couldn't have been bad.

Not ot sure if anyone knows the answer to this, but I have to wait a couple more weeks to see my neuro, and I'm curious. My VEP results are abnormal for my left eye. That eye also has amblyopia. Is it possible for them to differentiate if the latency is from the eye being lazy versus nerve damage?

[jreagan70]

My VEP results are abnormal for my left eye. That eye also has amblyopia. Is it possible for them to differentiate if the latency is from the eye being lazy versus nerve damage?

Depending some other aspects of your results, there might or might not be some difficulty telling what measurement is due to what. Neurologists aren't trained to know the difference, so it might be an interesting appointment for you.

One of the principles of diagnosing MS is that every other possible cause for signs and symptoms has to be ruled out first. The same applies to the test results. A VEP is nonspecific. So if there is another possible cause for the test results [in your case amblyopia, when (I'm assuming) the results for the other eye are normal], the test isn't as valuable in using it as supportive information.

If you really want to know what's going on with a VEP for an amblyopic eye and what it might mean for MS, see an ophthalmologist, or better yet, a neuro-ophthalmologist. Your neurologist isn't the right person for this one.