It is true that sophisticated optical systems were routinely designed before the advent of lens-design software: exquisitely capable microscopes, telescopes, camera lenses, and other optics designed by hand calculation served their purpose well. But fast computer calculation now allows the lens designer to find optimized solutions for very complex optical systems to take into account, to a highly precise degree, the effects of glass, fabrication, and mechanical imperfections; to easily add aspheric surfaces that reduce the number of elements, widen the field, and/or add other benefits; and so on.
As a result, skilled lens designers working closely with skilled optics fabricators now produce precision optics for purposes ranging from smartphone cameras to military infrared (IR) imaging, computer chipmaking, augmented/virtual reality (AR/VR), and many others.
A typical optical design software package can model an optical system via ray-tracing (with spot diagrams as the visual) or via wave-based physical optics calculations (with diffraction patterns as the visual), with the latter requiring more calculation. Imaging lens-design software has numerous offshoots, including non-imaging optical-design software, integrated CAD/CAM programs, and other derivatives, some or all of which may be incorporated into the original software package.