Why are RX Sunglasses Lenses so BIG?

[NightFox]

Hi!

For my normal glasses, I have a pair of prescription varifocal Oakley TinCups, which are nice and light. I decided to also upgrade the lenses on my Flak Jacket/Flak 2.0s from non-RX to varifocal RX (the same fairly low prescription) but was really taken aback when the lenses arrived at how thick and heavy they are. Given that my TinCup lenses are no thicker than my non-RX sunglasses ones, I expected the RX ones to be similar, but to give an example of the Flak Jacket Lenses:

Original (Non-RX)
Weight: 3g (0.1oz)
Max thickness: 1.7mm (.07")

RX
Weight: 11g (0.4oz)
Max thickness: 4.7mm (.18")

I've attached a picture of both lenses side-by-side for comparison.

Can anyone explain why these lenses are so bulky, particularly when the same prescription on my TinCups is about the same thickness as the non-RX FJ lens? Although you can't see the difference face-on when wearing the glasses, it's quite obvious from the side and I'm really conscious of the weight of the glasses on my nose as they're no longer nicely balanced so the arms don't really spread the load. They're certainly still wearable, but they're no longer the 'forget you're even wearing them all day' feeling that I'm used to.

Thanks,

Neil

 

[O Bro]

base curvature. Those Flaks have a lot more base curvature than Tincups, which is an RX specific frame that is very flat. The more curvature you have, the thicker the lens is going to be. They have to accommodate for the increased optical distortion of curved lenses. If you would like them to be thinner, you would have to switch to a flatter frame (sylas, holbrook, etc.)

 

[NightFox]

Got it, thanks for the reply.