Conventional hard resin lenses are half
the weight of glass lenses and can be tinted to almost any color and
intensity. Hard resin lenses are more easily scratched than glass but
can have an optional scratch protection applied. More impact
resistant than glass, hard resin lenses do not require tempering.
Lighter, thinner lenses
Modern technology has created lenses that
bend light differently so that stronger prescriptions are thinner than
when made in conventional materials. Such lenses are called
"high index" and stronger prescriptions are more attractive
because they are slimmer. Glass lenses are also available with the
slimming advantages of high index but are considerably heavier. High
index plastic uses less material, so the lenses are often lighter in
weight. High index lenses absorb all harmful UV light and can be
tinted to any shade of color.
Lenses that darken in the sun
These are photochromic lenses that darken as you go
from indoors to outdoors. They are available in glass, hard resin
and polycarbonate. Originally made to darken to a moderate shade,
new versions are available that darken to true sunglasses. Ask for a
demonstration of these lenses.
Polycarbonate lenses are the most impact
resistant lenses available and are always the lens of choice for
young people and active patients. Polycarbonate lenses are high
index and usually provide the lightest, most comfortable lenses.
They absorb all harmful UV light and can be made ultra thin because
of their unique strength.
For years glass was the only lens material
available, and glass still offers superior optics. The most
scratch-resistant material, the primary disadvantage of glass is its
weight, generally twice that of hard resin. Glass lenses are tempered by heat or
chemicals to increase impact resistance.