When a pilot flies at higher altitudes, his or her eyes may be exposed to higher levels of ultraviolet (UV) radiation. Exposure to UV radiation can lead to the development of cataracts and other serious eye problems. In addition, glare from the sun can make it difficult for an aviator to maintain positive situational awareness of his or her surroundings.
I suggest you choose some high-quality aviators sunglasses like Bolle, Oakley, Ray-Ban and Serengeti. And one pair of green lens sunglasses can protect the pilot's eyes both to prevent glare but also anti-ultraviolet