/ matterhorn sunglasses needed?
could snow blindness or strong sunlight higher up be an issue?
I think people overestimate the need for higher cat lenses. I did the Haute Route in very sunny conditions and felt fine using Cat 3's. I think just having good UV properties is the main thing. If you get a modern well fitted pair that sit close to your face i think you can dispense with the glacier style side flaps.
Dude, take a spare pair too. If you loose them you can get really stuffed.