There's an interesting Australian report regarding pilot lookout:
www.atsb.gov.au/media/32918/limit_see_
avoid.pdf
On page 9 there are theoretical reasons given why sea-and-avoid should only work a small percentage of the time. Arguably they're a bit pessimistic (e.g. in the circuit, you can to some extent predict where aircraft will come from, look in those spots, and improve your chances substantially; in the cruise, most conflicting aircraft are likely to be at your level, so you could see most but not all of them with a much narrower scan than the 180x30 degree scan specified).
Peripheral vision is good at motion detection, but it's the stationary, small aircraft that you're likely to collide with that you have to look out for, and you will see them best with your central vision that has good acuity. By the time they're large enough to be picked out in your peripheral vision, it's probably too late. So personally I'm sceptical that small-framed glasses would be that detrimental to lookout. Also, you can turn your head as well as your eyes, so the frames shouldn't cause 'blind-spots' to the same extent as pillars in the canopy may.
That said, there may be other times when peripheral vision is important - e.g. landing.
I used to wear contacts with wraparound glasses for hang-gliding, because it was much simpler and cheaper to update my prescription than to get prescription sports glasses made regularly. I found that the wind got in my eyes when I used regular spectacles. As someone with a real phobia of putting things in my eyes, it took me a lot of practice before I managed to get them in consistently, but I eventually got on well with them. I haven't felt a need for them recently though.
I've also asked opthalmologists (a profession that, like piloting requires both eyes) whether they would personally consider having laser treatment or using contacts... The answer has generally been 'no'.