In general, the invention is directed to an implantable medical device assembly having a more space-efficient housing and components, as well as processes for assembling the implantable medical device with reduced assembly cost and less complexity. The mounting base mechanism defines a first clamp surface having clamping engagement with one of the angulated clamp surfaces. The cartridge includes a longitudinal lumen from a loading chamber to an open distal mouth that gradually narrows in dimension so as to fold the IOL into a tube for insertion through an incision in the eye.