It would appear this is to do with the reflector as opposed to the lense. The following is copied from Wikipedia which of course is not always correct but who knows.
"Starting in the 1980s, headlamp reflectors began to evolve beyond the simple stamped steel parabola. The 1983 Austin Maestro was the first vehicle equipped with Lucas-Carello's homofocal reflectors, which comprised parabolic sections of different focal length to improve the efficiency of light collection and distribution. CAD technology allowed the development of reflector headlamps with nonparabolic, complex-shape reflectors. First commercialised by Valeo under their Cibié brand, these headlamps would revolutionise automobile design." Cheers David