A head-mounted device may have a display that displays computer-generated content for a user. The head-mounted device may have an optical system that directs the computer-generated image towards eye boxes for viewing by a user. The optical system may be a see-through optical system that allows the user to view a real-world object through the optical system while receiving the computer-generated image or the optical system may include a non-removable lens and a removable vision correction lens through which an opaque display is viewable. The optical system may include a removable lens. The removable lens may serve as a custom vision correction lens to correct for a user's vision defects. The optical system may have a projection bias lens that places computer-generated content at one or more desired virtual image distances and a corresponding compensation bias lens.