Sunglasses with detailing or width concentrated at the top of the frame (browline styles, or frames with a bold upper rim) draw the eye upward, away from an already-wide jaw.
The Styling Principle
Add width and volume at the forehead and temples while keeping the jaw area closer to the head, which brings the upper and lower face into better visual balance without hiding the jawline entirely. Sunglasses with detailing or width concentrated at the top of the frame (browline styles, or frames with a bold upper rim) draw the eye upward, away from an already-wide jaw.
Sizing
As with prescription frames, sunglasses width should roughly match your face's widest measurement — for a triangle face that means sizing relative to cheekbones.