You probably have a pretty good idea of what kind of
frames you want. But the most important part of the eyewear, the
lenses, is largely a mystery for most of us. Your professional
optician will guide you expertly through the many choices
available, so you get the lenses best suited for you
prescription and lifestyle. This list is a brief overview of the
major types of lens options you will want to discuss with your
Hard Resin (plastic)
Conventional hard resin lenses are half the weight
of glass lenses and can be tinted to almost any color and
density. 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 heat treating.
Modern technology has created lenses that bend light differently so
that stronger corrections are thinner than when made in conventional
materials. Such lenses are called "high index" and stronger
corrections are more attractive because they are thinner. 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 or color.
Lenses that Darken in the Sun
These photochromic lenses darken as you go from indoors to outdoors. They are available in
both glass and lightweight hard resin. They darken to a moderate
shade of grey. A demonstration of these lenses is the best way to
learn about their properties.
This is the most impact resistant lens material available and are
always the lens of choice for young people and other active clients.
Polycarbonate lenses are high index and are usually the lightest,
most comfortable lenses. They absorb all harmful UV light and can be
made with ultra thin edges 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 heat or chemically treated to increase
Single vision lenses
Single vision lenses function as all purpose glasses for persons who have normal
accommodation. Persons who normally wear bifocals or trifocals can
use single vision for distance or near lenses. Single vision lenses
can also function as occupational glasses for certain types of work.
Single vision lenses are available in all lens materials.
These lenses provide special visual and cosmetic benefits for stronger corrections and
increase edge to edge clarity. Flatter than conventional lenses,
aspherics eliminate the "bulgy" appearance of strong plus lenses and
greatly enhance the appearance of finished eyewear. Persons with
strong nearsighted corrections also benefit from thinner, lighter
weight glasses when their lenses are aspheric. Because aspheric
lenses are positioned closer to the face, there is less eye
magnification with farsighted corrections and less of the "small
eyes" look with nearsighted corrections. Aspheric lenses are often
made of high index materials for the ultimate in thin lenses.
This is the most popular
bifocal format and is available with the bifocal portion made in a
variety of widths to help with various close-up occupations.
Flat-top bifocals are made in every type of lens material.
Franklin Style Bifocals:
Sometimes used for those
who need a wide field of vision for near work (accountants, for
example), Franklin style bifocals have a distinctive appearance and
are thicker because of their design. They are generally only
available in glass, hard resin and photochromic glass. They are
being replaced by wide flat-top bifocals.
Trifocals come in a variety of designs. Flat-top trifocals are the most widely
used form. The added segment provides clear vision at arm's
length distance, the area that is usually blurred for
bifocal wearers. Trifocals are available in all lens
Progressives (no line bifocals)
These lenses provide all the benefits of bifocals but add the feature of
continuous clear vision at all distances, including
mid-range distance (arm's length). Progressives have the
cosmetic advantage of appearing to be single vision lenses
so they never reveal that the wearer is using bifocals.
Progressives are available in all lens materials and also
made in aspheric form. Because of their many benefits, they
are becoming the lens of choice for bifocal and trifocal
Many occupations impose demanding visual requirements on those who wear
bifocals or trifocals. In addition to safety concerns, be
sure to discuss the wearer's job tasks so the lenses can be
designed for specific requirements.
All sorts of special lens designs are available for the needs of sports
enthusiasts. Polycarbonate is the material of choice for
active sports. (See the August 1996 Opticianry Today for an
overview of visual requirements for selected sports
activities.) Polarized sun lenses that eliminate reflected
glare are especially appropriate for drivers, fishermen,
hunters and all types of outdoors activities.
There are a variety of options for those who use computers. These include special filters
and anti-reflection coatings.
Optional Lens Treatments
Scratch Protection Coating
Light weight hard resin lenses can be more easily scratched than glass lenses. Special
coatings have been developed to help protect lenses from normal
scratching. The modest additional cost for such scratch coating is
a prudent investment.
It is generally accepted that the ultraviolet rays in sunlight pose
potential harm to the eyes. Special treatment for hard resin
lenses completely blocks hazardous UV light. Lenses like
Polycarbonate and high index include built-in UV protection.
Special anti-reflective coatings, much like those used for fine
camera lenses, are available for spectacle lenses. These
coatings are particularly effective for reducing eye fatigue
for computer operators and anyone driving at night. And, of
course, AR lenses enhance appearance by removing all
distracting reflections. After you have discussed the ways
in which you will be using the new glasses, you can choose
the exact combination to effect the "magical" result of
better vision and eye protection.