A head-mounted device may have optical modules that present images to the user's left and right eyes. The optical modules may move with respect to each other to accommodate different user interpupillary distances. Each optical module may have a lens barrel, a display coupled to the lens barrel that generates an image, and a lens mounted to the lens barrel through which the image is viewable from an eye box. The lens may be a multi-element lens formed from molded lens elements such as molded polymer lens elements. A lens element may be provided with protrusions that form lens tabs. The lens tabs may have coplanar lens tab surfaces that mate with corresponding coplanar mounting surfaces in the lens barrel. Alignment marks may be formed on the protrusions and/or other portions of the lens.