Glass was the first lens material used to make modern-day eyeglasses. Its earliest use is documented back to the 13th century in Venice, Italy. It remained the only lens material choice for almost 600 years until the introduction of plastic lens materials in the mid 1900's.

Glass lenses have excellent optical qualities and can have a refractive index as high as 1.90. But safety standards require a lens center thickness of 2.0 mm for glass as compared to half that thickness or 1.0 mm center thickness for 1.60 or 1.66 high index plastic. This requirement is why glass lenses need to be thicker than newer lens materials like high index plastic. Glass lenses are heavy and uncomfortable to wear. Stronger lens prescriptions give the unsightly "coke bottle" or "bug eye" look to the lens wearer.

PROS OF GLASS

• doesn't scratch as easily as plastic
• has excellent optical qualities

CONS OF GLASS

• heavy to wear
• uncomfortable, constantly slides down one's nose
• strong minus prescriptions have unsightly edges giving the notorious "coke bottle" effect or the "bug eye" look of high plus prescriptions
• poor impact resistance as compared to high index plastic and polycarbonate