Glass, Lenses - What are the most commen lens manfucaturers?

I'm studying to be a dispensing optician soon and would like to know the most common lenses like nikon etc.more to do with glasses frame lenses.

Yes, some manufacturers for precission optical make camera lenses too. Or reverse. Carl Zeiss was one of the formers, Schneider Kreuznach, Leica make lenses and microscopes and telescopes, Nikon also makes lenses for its cameras, Hasselblad also, I think Mamiya too. Olympus too. And I think Canon and Pentax. Voigtländer made lenses since 1756 and I believe it's no longer making cameras. Well, probably there would be more