We use digital, or surfaced, lenses instead of standard stock lenses. Digital lenses are cut for each prescription. They cost more, but provide better clarity and minimal edge-to-edge distortion.
We use aspheric instead of spherical lenses. Aspheric lenses reduce magnification, so you don't get a fishbowl effect. They are thinner and lighter. And they provide better optical quality with less blur.
Product Description for Leader xRx Eyeglasses Custom Rx-able Swim Goggle Junior w/Rx Yellow