Angular sunglasses frames — square or rectangular shapes with defined corners — work against a round face's natural softness better than round or aviator styles, which echo the existing curve.
The Styling Principle
The objective is to introduce visual length and angularity — height at the crown, vertical lines near the face, and any structure with a defined corner (a squared frame, an angular jaw-grazing cut) reads as elongating against the face's natural softness. Angular sunglasses frames — square or rectangular shapes with defined corners — work against a round face's natural softness better than round or aviator styles, which echo the existing curve.
Sizing
As with prescription frames, sunglasses width should roughly match your face's widest measurement — for a round face that means sizing relative to cheekbones.