I am pretty sure, diamonds would make awful eyeglasses. While their index of refraction is high, which makes glasses thin, their chromatic dispersion is high. That is the very thing which makes their glitter so colorful. For good optical systems you want to try to reduce the dispersion, to 0, if possible.
Another story is the scratch-resistance. For that it would be sufficient to coat the surface of the lens with a thin layer of diamond. Which is done in several applications.
Another story is the scratch-resistance. For that it would be sufficient to coat the surface of the lens with a thin layer of diamond. Which is done in several applications.