How long does a VEP take?

I've already had a MRI, MRA and a Lumbar Puncture (spinal tap). I am having a VEP on the 18th. I understand they are basically non-invasive. What exactly do they do and what are they looking for? Thankfully I don't have an visual problems yet. How long do VEPs usually take?

Thanks!

[COBOB]

About an hour.  You sit in front of a monitor with electrodes attached to your scslp and you watch the checkerboard switch back and forth.  They test one eye ate a time several times on a few different sets of patterns.  They are looking of the time between the change in pattern and the response on the visual cortex of the brain.  The pisutive peal (P100) should be less than about 115 miliseconds.  More than that indicated latency (decreased conduction velocity) of the optic nerve and is typical in Optic Neuritis.  

Bob

[COBOB]

That should have been "Positive Peak."  Tired eyes and unreliable fingers/typing skills.

[MomofTwo83]

Are VEPs the same as visual field tests?

[twopack]

No, that one has you focusing on a center point (with one eye covered and then the other) while small points of light flash in 'random' areas all around your peripheral vision.  You press a jeopardy type button every time you see a flash.  This is a super mega deluxe version of the mini test used to screen applicants for a driver's license.

The visual field looks for areas you are not seeing or are not aware of seeing, blind spots.

The VEP (or VER) measures how long it takes your brain to get the message that the image your eye is looking at has changed (and it doesn't matter if you think you saw it or not).

By the way Ojibajo, the electrodes are "glued" on.  NO NEEDLES stuck in you.  It can leave you with eyeballs that feel strained and tired but it's not invasive in the breaking through skin manner we dread and no prep necessary.

Mary

[Ojibajo]

Thanks for your answers. Like many on the forum I don't have an understanding boss and I work in a very dysfunctional office. So anytime I miss work for a doctors they all assume I must be at the mall or at Disney Land. so I am expected to be back to work afterward.

It really ***** because most days for the past six months I have felt like complete crap, but what can you do? I just pray I find a better, more manageable job soon.

Thanks again.