why do i get nauseated when i change from contact lens to glasses or vice versa?

Question

i wear contact lenses when i am at work or play, but about two hours to bed i change to my glasses, and am immediately hit by a bout of nausea that lasts till i fall asleep. Would someone please tell me why? am short sighted

Answer 1

Essentially it boils down to mismatch between what your eyes are telling your brain about your position and what your inner ear is telling you about your position.

You brain has an incredibly precise mechanism for keeping your eyes fixed on an object when your head moves (the occulomotor reflex). Essentially it figures out how much your head moved, and moves your eyes the oppose it.

However, the mechanism has the ability to learn. When your wear glasses, or contacts, you slightly warp the image of the world (if you look at the edge of your glasses, you should see that the through the glass image doesn't quite line up with the real image).

Your brain deals with this constant bias in your vision so that your occulomotor reflex works again. However, when you swap to your glasses, this modulation of the relfex no longer works, and you get a mismatch again.

This mismatch makes you sick because a lot of poisons (think ethanol) can make you dizzy (i.e. a bad mismatch). A good response to eating a poison is to vomit. When the effect isn't so strong as to make you vomit, you just get nausea.

Answer 2

You must be very near-sighted or very sensitive. When you take out your contacts and put the equivalent power in front of the eye by several millimeters to an inch you will get a swing in your vision. The items that you are looking at will move or sway in the opposite direction that you move your eyes. It is like a motion sickness.
If your glasses are older than your contact lens prescription try having your eyeglass lenses updated. If they are the same prescription as your contact lenses try wearing an older pair of glasses. Each person is different in the way that they respond to the switch from glasses to contacts, you just have to find which way is most comfortable for you.