An interior rearview mirror assembly for a vehicle includes a mirror casing and a prismatic interior reflective element. The reflective element comprises a wedge-shaped glass substrate having a perimeter edge about a periphery of the glass substrate and extending between first and second surfaces thereof. The glass substrate has a mirror reflector established at the second surface. A front surface of the perimeter edge provides a smooth curved transition at the perimeter edge between a perimeter region of the first surface and the mirror casing. The front surface of the perimeter edge is rounded with a radius of curvature of at least about 2.5 mm. No portion of the mirror casing encompasses the first surface of the glass substrate.