Thin & Light Lenses
Lenses needn’t be thick and heavy. This is a wide range of thinner
materials, which can reduce thickness and weight by up to 45%. These
thinner lenses are often referred to as ‘high index’.
Lens Index
Every lens material has what is referred to as a ‘refractive
index’. The index is a numerical figure and for lenses ranges
from1.5 to 1.9.
The higher the index, the thinner the lens is.
Lenses are classified as being either ‘Standard, Mid, High or
Super High Index’. Both Glass and Plastic lenses are available
in all four types. |
| |
| LENS TYPE |
LENS INDEX |
% THINNER THAN STANDARD 1.5
LENSES |
| Standard Index |
1.5 |
This is normal thickness |
| Mid Index |
1.6 |
Approx
30 % thinner |
| High Index |
Varies
from 1.67 to 1.7 |
Up
to 40 % thinner |
| Super High Index |
Varies
from 1.74 to 1.9
|
Up
to 50 % thinner |
|
| |
Glass or Plastic?
Plastic lenses are not currently available in
as high an index as glass. The highest index plastic is a 1.74, whereas
Glass indices go up to 1.9. Very strong prescriptions will therefore
be thinner in glass. For most prescriptions however, plastic is usually
the first choice as it is much lighter and is safer
Other Ways of Reducing Thickness
As well as choosing a Higher Index material, there are other things
that will help to reduce the thickness:
Aspheric (Flatter) Lenses
These are not as curved as regular lenses.
In general the flatter the curvature of the lens, the thinner it is,
both in long and shortsighted prescriptions.
Custom Surfaced Lenses
These are lenses that are custom made
to the minimum thickness possible for the selected frame and individual
facial dimensions. They make a big difference on longsighted prescriptions.
Thin & Light Lenses are available in clear, tinted & photochromic.
|
| |
|
|
