An interior rearview mirror assembly for a vehicle includes a mirror casing and a prismatic reflective element, with the mirror casing adjustably supported at a mirror mount at an interior surface of the vehicle. The mirror casing includes a principal mirror casing portion and a pivotable mirror casing portion that is pivotable relative to the principal mirror casing portion. A toggle assembly includes a toggle lever and a spring element disposed between and coupled to the toggle lever and the pivotable mirror casing portion of the mirror casing. Pivotal movement of the toggle lever flexes the spring element and adjusts the angle of the principal mirror casing portion and the prismatic reflective element relative to the pivotable mirror casing portion of the mirror casing.