Exposure to ultraviolet (UV) radiation from sunlight has been associated with the development of cataracts and age-related macular degeneration (AMD). Quality sunglasses protect your eyes by blocking 100 percent of the sun's harmful UV rays. UV rays can also cause wrinkles and premature aging in the delicate skin around the eyes.

Sunglasses are an effective wind barrier. Wearing them reduces the rate of tear evaporation and helps keep your eyes moist and comfortable. They help prevent contact lenses from drying out and windblown particles from causing a corneal abrasion. Close-fitting, "wrap" style sport sunglasses are particularly effective at reducing the potential for dry eyes and eye injuries.

The pupil controls how much light reaches the light-sensitive retina in the back of the eye. In dim light, the pupil increases in size (dilates) to allow more light in. In bright light, the pupil constricts to keep too much light from striking the retina. In very bright conditions, the pupil cannot constrict small enough to reduce light to a comfortable level. This causes a person to squint. Muscle fatigue associated with squinting and constant constriction of the pupil can lead to headaches and eyestrain. Sunglasses reduce the amount of light reaching the eyes to a more comfortable level, eliminating the need for squinting and severe pupil constriction. This increases comfort and reduces headaches and eyestrain.