How to buy sunglasses

Summer, on the road a lot of women are wearing the sunglasses, not only to add summer charming style, but also to prevent the scorching sun on the role of eye irritation, but many women choose to have only thought of sunglasses styles, to the neglect of color, lenses, anti-UV index and internal factors, not only due role sunglasses, will have a serious dizziness, swollen eyes and so are not suited acid symptoms, and sometimes have been insensitive, color vision illusion walk inequality symptoms, and may even lead to accidents, etc., so good to buy sunglasses. 
UV damage to human eyes, mainly on the wavelength of UV radiation time and radiation intensity as well as human eyes, strong or weak self-defense mechanism, and the cornea, lens, the retina is the most commonly damaged by ultraviolet rays of eye tissues. In an ultraviolet eyes 6-8 hours later, his eyes at the same time, foreign body tingling and gradually add to produce pain, photophobia, tears, eye spasm, conjunctival congestion, are eyes sunburn performance will appear serious large areas of corneal epithelial exfoliation, symptoms such as vision loss, and sunglasses have been able to block ultraviolet rays, is because the lens add a layer of a special coating, in blocking the absorption of ultraviolet, but also blocked part of visible light, so that the lens of the light transmission declined, so high-quality sunglasses block UV ability, transmittance will not decline a lot, and a certain degree of hardness of the coating difficult to wear. 
A pair of sunglasses to identify whether there are anti-ultraviolet function, can in some product labels or lenses to see, such as UV, UV400 obvious logo. UV index is to filter out the effects of ultraviolet radiation, which is very important to buy sunglasses in an indicator. Wavelength at 286nm-400nm, known as ultraviolet light, generally 100% of the UV index is impossible, the vast majority of sunglasses the UV index of 96% ~ 98%. 
In fact, marked as the UV400 sunglasses, have been able to reach more than 90% of defense ultraviolet function, the lens through special processing, can block the ultraviolet wavelengths less than 400nm, and may choose to wear contact lenses with anti-ultraviolet function of contact lenses, can filter out 90 percent of ultraviolet rays, and then wear sunglasses, security on the higher levels.