What causes my eyeball to occasionally twitch?

Here is a great article:

http://www.mayoclinic.com/health/eye-twitch/AN0088...

Do you mean eyelid or eyeball ?? If it's your eyeball, it should not twitch. There could be an underlying physical or neurological ailment. With some people, the muscles that surround the eye can become weak and therefore,the eye itself cannot be maintained in a stationary position. The eyeball can then move involuntarily, without purpose. My best advice would be to contact your Doc so she/he can determine the cause. How long has this been happening?? I hope that this helps.

usually it's from eye strain, too much reading or looking at a computer screen. Sometimes it can be a nervous reaction. Rarely is it anything to worry about.

I have that.. Honestly its from lack of sleep. Or if you are getting enough adequate sleep it can also be cause by not drinking enough water or it is a nervous tick or twitch