When I'm thinking of the most crucial discoverys of science than I think of the lens invented in the 16e century. By using a lens man could make microscopes and telescopes. When I think about that than I can't imagine that people had gone to the moon, had a mobile telephone, can listen to the radio watch tv, use GPS. But is through that the invention of the lens was crucial for futher technological inventions or could man invent those things via an other way and was it not really necessary?
First of all, the lens was discovered much earlier than 16s century. The properties of the convex lens were described by Alhazen in his Book of Optics in 1021. The eyeglasses were invented in Italy in 13s century. This is by far the most important use of lens.
Notice that most humans after the age of 40 need eyeglasses just to be able read and write (and do many other jobs). And many people need them before 40. So this invention substantially prolonged the active life of people of many professions, including scientists and inventors. So certainly many discoveries in all areas would not be made without this invention.
Another invention based on the lens, which affected the life of most humans is photography, with all its subsequent derivatives including cinema, video and TV. All this would be impossible without lens.