Actually, in the years before lasers (an even occasionally nowadays), obsidian was used in scalpels for eye surgery, since it holds a better edge than steel. Of course, lasers don't even have edges, so they have mostly replaced scalpels of any material.
One also has to remember the scene from Snow Crash where YT's skateboard's sonic wave hits the guy with the glass swords: it's the same idea. Glass and obsidian are easily among the sharpest things the average person can ge their hands on.