Eyelids and tears work together to protect the eye against damage. The eyelids act as shutters, closing to stop material from entering the eyes. Tears contain one of the most potent antiseptic substances known, called lysozyme. It keeps the surface of the eyes moist and helps prevent infection. Disorders of the eyelids or tear system can damage the eyes, but most are easily treated if detected early.

The upper and lower eyelids provide essential protection for the eyes. If anything approaches the eye or face rapidly, the eyelids close together almost instantaneously as a reflex action. Furthermore, each eyelid has two or three rows of eyelashes, which help prevent small particles from entering the eye.

Tears are another important part of the eye’s defences. They are made up of salty fluid produced by the lacrimal (tear) glands, which are located above the upper eyelids. Tears lubricate the exposed surface of the eye and wash away potentially harmful materials, such as dust and chemicals. The production of tears can lessen with age, which is why wearing contact lenses can become increasingly uncomfortable as we age. However, dry eyes per se can be part of a syndrome called Sjogren’s syndrome, with arthritis and a dry mouth as well as dry eyes.