In article
<10ac0ca2-dd31-44f1-83f5-e5aff55f81f7@b1g2000hsg.googlegroups.com>,

Glass usually is denser than plastic although the difference in weight
is often exaggerated. As a rule of thumb, high density glass has higher
refractive index than low density glass. This leads to thinner lenses.

One time when I was more involved with selecting glass, many of the
higher density glass lenses could weigh less than the equivalent in low
index. This is especially true of large diameter lenses for myopia.
Negative lenses are thicker at the edge. If you neglect the thickness of
the lens in the center, the weight will go up approximately as the
fourth power of the diameter.

In my case, I have had cataract surgery on both eyes. The implants
reduced the (negative) power required from external lenses. Thus, The
weight of my spectacle lenses are muchlower than what they would be
without surgery.

Bill

Considerably.  They used to be cheaper than plastic, too.  Hard to find
and expensive now.