Jeez!,five pages of replies and nobody has mentioned the CAA/JAA/BALP/IFALPA etc approved scientific "Sunglass aquisition method"
Enter terminal sunnie shop in full uniform and preferibly in view of Swedish ladies beach volleyball team in lounge.Try on a few pairs while gazing in mirror.Convince yourself you look the mutts nuts.Justify huge expense with some of the bollox from earlier replies to this post.
Don't worry about those headaches,wavy lines on the screen,catteracts etc-You're a steely eyed jet jocky/ sky god fer chrissakes!!