Many people use a pair of sunglasses for many years. In fact, sunglasses also have a shelf life, which is related to wearing time, lens material, wearing habits, and regional sunshine. Generally speaking, the optimal service life of sunglasses is approximately two years. So it is best to replace them with a new pair after exceeding this limit.

First of all, the main wear and aging areas of sunglasses are the joints between the lens and the frame. Currently, there are three main types of lenses: resin polarized lenses, resin PC lenses (AC, CR39, and nylon are temporarily included in this category), and glass lenses. Resin polarized lenses and resin PC lenses that are lightweight and comfortable are not wear-resistant, and can cause scratches over time. Many people do not know that the lens is worn out, and relying on eye adjustment to try to see clearly can increase fatigue in the long run, leading to decreased vision. Therefore, usually, the lens should be placed upward to avoid  scratches on the lens surface.

Secondly, prolonged exposure to sunlight on lenses can reduce their UV resistance and easily cause corneal damage. Through simulation experiments, researchers placed sunglasses under a solar simulator at a distance of 30 centimeters from the light emitting point, and continued to "expose" them for 50 hours. They found that the UV resistance of the lenses would deteriorate. The highest UV levels in tropical countries and regions mean that the UV protection function of sunglasses degrades faster in these areas. Even if special materials are used for the lens material of high-quality sunglasses, they will still age over time. If the UV protection function of sunglasses decreases, it can damage the cornea and retina, leading to diseases such as solar keratitis and corneal endothelial damage.

High quality sunglasses can absorb or reflect ultraviolet rays to block exposure to the eyes. There are several explicit ways to do so: 1. Mark "UV400" to indicate that the lens has a UV isolation wavelength of 400 nanometers, which means that the maximum spectral transmittance below the wavelength of 400 nanometers cannot be greater than 2%. 2. Mark "UV" and "Anti UV": indicating that the UV blocking wavelength of the lens is 380 nm. "100% UV absorption" indicates that the lens has a 100% UV absorption function, and the average transmittance in the UV range is not greater than 0.5%. Only those with the above markings can be considered as sunglasses that have a real protective function against ultraviolet rays.

In addition, sunglasses belong to the flat lens series, and can only have a diopter of plus or minus 8 degrees at most. Exceeding this error range is considered an unqualified product. According to market testing, nearly 30% of sunglasses have diopters that exceed the error range, and some even reach as high as over 20 degrees. Consumers with normal vision who wear these sunglasses are like wearing a pair of nearsightedness glasses or hyperopia glasses. After a summer, they will be "cultivated" by inferior glasses as nearsightedness or hyperopia patients. Therefore, if symptoms such as dizziness, nausea, and eye shaking occur after wearing sunglasses, they should be immediately removed.

You should go to a regular store to buy sunglasses. Some cheap sunglasses not only cannot filter out ultraviolet rays, but also can block out visible light, making the ultraviolet radiation more noticeable. Be careful not to wear sunglasses for a long time, otherwise your eyes will be tired. Sunglasses should be removed when entering indoors from outside. Don't choose sunglasses with large frames, as they can increase the burden of eye adjustment and damage vision.