I am currently in need of corrective glasses.
What are my options as I would like to "combine" my corrective glasses with sunglasses. Is a clip on sunglasses the only option?
Photochromatic is out, as suggested from an ealier post...
Any special cylindrical aberration and at which dioptric power - so, how expensive would custom built be? Keep in mind, if you are in need for corrective lenses, you have to have two sets!
Photochromatics are out, oh yes, same as polarized glasses are an absolute NoGo, especially since glasscockpits become more and more common, but also because many instruments now use electronic screens with polarization.
I would go for custom made plus a clip-on. The clip-on to your ordinary lenses are backup, so you comply the second pair requirement. When I had to go corrective lenses for reading only, I took the nice lady of the shop to my plane to let measure in the exact onset position for the reading lens insert: I sat in the plane at the usual flying position and she measured the position of the line of sight of the glareshield. This was recommended by the lady, who is a pilot by herself, because the reading lens inserts in common corrective glasses are too far up for use in the cockpit (making a stiff neck from unusual positioning of the head). When I received my sunglasses I was amazed how good they are adapted to flying needs and yes, if I put them next to my standard "ground-use" glasses, there is noticable difference. So, if you go custom and I would advice to, let it done to fit to your usual plane.