CBSE Class 10 Answered

The eyelids are folds of skin controlled by muscles that can expand and contract very rapidly. Between our eyelashes, just inside the rims of the eyelids are 20-30 sebaceous glands as well as tear glands. When we blink, these glands secrete lubricants that prevent the eyes from drying out. Each time the eyelids close, salty secretions from the tear glands sweep over the surface of the eye, flushing away small dust particles and lubricating the eyeball. Our eyelashes serve as dust catchers, because the reflex action of blinking automatically causes them to lower when exposed to some kind of foreign particles.
If you are in irritating conditions such as a smoke-filled room, you blink more frequently to keep the eyes clean and moist. You should also blink more often, even consciously, if you wear contact lens or sit before the computer screen for long periods of time.