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 by at least one of grinding and polishing to provide a generally rounded curved surface between the first surface of the glass substrate and the mirror casing. The radius of curvature of the front surface is at least about 2.5 mm. No portion of the mirror casing encompasses the first surface of the glass substrate.