I think Optics and glass in general (a transparent yet solid material).
Without Optics, any discovery that was aided by a magnification either by a microscope or telescope wouldn't exist.
Even without standard, non-magnifiying glass the world would be a vastly different place.
There would be no light bulbs, every source of illumination would have to be natural light or a naked flame.
Transport would be drastically reduced. Cars would be limited to speeds that are tolerable with an open cockpit and with no goggles or visors, also travelling at night would be very difficult without proper illumination.
While powered flight may exist, speeds, distances and altitudes would be restricted to how much the pilot's bare face and eyes could tolerate.
Ocean travel would be severely limited without telescopes and a covered navigating position. While you could build a covered ship that is protected from the elements, without glass some crew are going to have to be outside at all times so you can see where you're going. Submarines wouldn't exist at all (you'd be completely blind underwater).
While electronics and computers wouldn't be reliant on glass as such, without optics we'd only be able to miniaturise things that were visible to the naked eye, so no Microchips or tiny components.
Anyone with sight problems would just have to put up with them and without corrective lenses, society would be drastically different, because anyone with 20/20 vision would be literally superior and highly valued.
I probably haven't even scratched the surface of how important glass and Optics are to Human history and development. It's easy to take it for granted because it's so commonplace, but without something as simple as a material that is solid yet transparent, the world would be unrecognisable.