What are some of the eye's natural defenses that help to prevent infections?

Blinking: Blinking, watering and eye lashes are three natural defenses.

Several: The first line of defense is the skin on the eye's surface, which acts as a barrier to infection. The tears contain antibacterial compounds, and when blinked away, carry infectious organisms with them off of the eye's surface. Eyelashes can catch larger particles that contain germs before they land on the eye.