Sunglasses aren't just a fashion statement or another prop for celebrities to mask their identity - they also protect the eyes.

"Sunglasses are more than just an accessory," says Lu Yanyun, director of the Optometry and Glasses Center at Beijing Tongren Hospital.

"They can provide our eyes very powerful protection against bright sunlight."

Excessive exposure to sunlight, including both visible and invisible sunlight, can cause more than just discomfort, and the most common form of damage comes from ultraviolet and blue light, Lu explains.

Ultraviolet light, mostly ultraviolet A and ultraviolet B, can cause short-term and long-term eye problems, such as cataracts, snow blindness, and eye cancers.

High-energy light, which includes blue light, is thought to be a cause of age-related macular degeneration.

Macula is an oval-shaped, highly pigmented yellow spot near the center of the retina, and acts as a natural sunblocker that absorbs excess blue and ultraviolet light. It is also responsible for central, high-resolution vision.

"A pair of sunglasses can efficiently cancel out the blue and ultraviolet light, thus protecting the optic nerve and macula," Lu says.

"But the prerequisite is that the sunglasses are of good quality and well-chosen."

When choosing sunglasses, the first thing to make sure is that the product has a quality certificate.

Sunglasses from a hawker may look like those in a reputable glass store, but the quality gap is wider than the price difference, Lu notes.

"Pay attention to certified manufacturer labels on the glasses that reflect the ability of the glasses to shield ultraviolet light," Lu says.

Another thing to consider is the color of the lens.

The color can vary depending on style and purpose, but for daily use, gray, green, brown and other comfortable colors are recommended, as they can maintain true vision and increase color contrast.

On the other hand, candy colors and bright colors should be avoided because their ability to cancel out light is limited, and they can distort vision, Lu suggests.

The shape of the glass frame is a personal choice, but bear in mind the curve of the frame should be not too dramatic, or, the lenses will practically become a prism and distort the vision.

Last but not least, people with eye problems, such as abnormal intraocular pressure and glaucoma, need to consult an optician on whether to wear sunglasses.

"A pair of ill-chosen sunglasses will harm the eyes. Always buy them from a qualified store," Lu says.

China Daily