If any microorganism gets in your eye, it will usually be washed out of the eye by your tears and the sweep of the eyelid. If you're wearing contacts, it can g

If any microorganism gets in your eye, it will usually be washed out of the eye by your tears and the sweep of the eyelid. If you're wearing contacts, it can get trapped in the film of liquid between the contact lens and the cornea, or in the film around the edge, and the tears and eyelid sweep will not be able to eliminate it. It's then in an environment where it's free to multiply and cause problems.