Even with contacts, having sunglasses that allow you to see when you move from sun to shade remains an issue. My best bike purchase this summer was a pair of Tifosi sunglasses that not only are photosensitive, but go almost clear in low light situations.
For the record, I'm blind as a bat and wear gas permeable sunglasses. I've never tried riding with my glasses on and I imagine I'd have peripheral vision issues. I just see much better with my contacts. I lost one on a ride last year, but I've otherwise had few issues with them. I absolutely must have sunglasses on when I ride though. Dirt, debris and the like are a no no with the gas perms.
To be honest, I don't know if taking your sunglasses off when you come into a shady area is the easiest solution. At least in my neck of the woods, shade is synonymous with bad drainage and potholes. Both hands have to be on the handlebars.....
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher