Lens shape
The outline of the lenses in a frame: round, oval, rectangular, square, cat-eye, aviator and more.
Also: frame shape
Lens shape is the first thing people notice in a frame. Common shapes are round, oval, rectangular, square, P3 (a rounded-off triangle), cat-eye, aviator teardrop and geometric hexagons. Opticians often use the balance-and-contrast rule: rounded lenses on angular faces, angular lenses on round ones. Lens height also matters for varifocals, which need enough depth for the reading zone. Very small lenses can leave the edge of vision uncorrected, so most people choose a shape a little larger than the eye.