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high
index
Keeping Your Grip on High Index
Materials
The many high index lens
materials available today enable ECPs to provide their patients with
thinner, flatter, lighter, and more comfortable
eyewear.
By Randall L. Smith, MEd,
ABOM
With all the lens materials available
today, it’s getting a little difficult to keep track of them all,
especially in the high index category. To help you keep your grip on
these products, here’s a quick overview of the advantages of high
index materials and what’s out there.
What’s High?
Although no formal classification of
refractive index has been established, most eyecare professionals
recognize the following delineation:
•Low index – <1.53
•Mid
index – 1.53–1.58
•High index – l.59–1.66
•Ultra-high
index – >1.67
Thinner Lenses
High index lens materials produce thinner lenses. The
higher the index, the greater the reduction in thickness. The
reduction can be dramatic for patients with high refraction
corrections. Some high index lens materials, such as polycarbonate,
can even be made with a 1mm center thickness.
Flatter Profile
High index lenses have a lens profile that is flatter
than lens materials producing the same power. A flatter profile
enables the lens to shed thickness. As the index goes higher, the
lens’ profile gets flatter. This is a welcome advantage, especially
for strong prescriptions. In today’s ultra-lightweight rimless
mountings, high index lenses look more attractive with strong Rx’s
because they look more like planos.
| High and Super-High Index Lens
Materials |
| Material |
Manufacturer |
Refractive Index |
Specific Gravity |
ABBE
Value |
| High Index |
|
|
|
|
| Polycarbonate |
Many |
1.59 |
1.21g/cm3 |
42 |
| Finalite 1.6® |
AO SOLA |
1.60 |
1.23g/cm3 |
42 |
| Thin&Lite® 1.6 |
Essilor |
1.60 |
1.34g/cm3 |
36 |
| EYAS® |
HOYA |
1.60 |
1.34g/cm3 |
42 |
UltraThin™ UV 1.60 and
UltraThin 1.60
AR |
Pentax |
1.60 |
1.34g/cm3 |
42 |
| Super 16 DC & AR |
Seiko |
1.60 |
1.22g/cm3 |
32 |
| 1.6 EvoClear™ |
Signet Armorlite |
1.60 |
1.34g/cm3 |
32 |
| Ultra High Index |
|
|
|
|
| High Index 1.66 |
AO SOLA |
1.66 |
1.36g/cm3 |
32 |
| Hyper 1.66® |
Optima |
1.66 |
1.36g/cm3 |
32 |
| High Index 1.67 |
Carl Zeiss Vision |
1.67 |
1.36g/cm3 |
42 |
| Thin&Lite 1.67 |
Essilor |
1.67 |
1.36g/cm3 |
32 |
Ultra Thin UV1.67® and
Ultra Thin
1.67 AR |
Pentax |
1.67 |
1.36g/cm3 |
32 |
| Super SV DC and AR |
Seiko |
1.67 |
1.36g/cm3 |
32 |
| 1.67 MR-10 |
Younger |
1.67 |
1.36g/cm3 |
32 |
| EYRY |
HOYA |
1.70 |
1.41g/cm3 |
36 |
| Thin&Lite 1.74 |
Essilor |
1.74 |
1.46g/cm3 |
33 |
| High Index (glass) |
Vision-Ease |
1.80 |
3.66g/cm3 |
25 |
Comfort Factor
All high index plastic lens materials are
lightweight—some more than others. Lens material weight is
determined by the material’s specific gravity (see “High and Super
High Index Lens Materials” at left). The lower the value, the
lighter it is. Polycarbonate; Finalite 1.6® from AO SOLA; and Super
16 DC from Seiko Optical Products of America, Inc. all weigh in
around the same low value making them excellent lightweight
choices.
Lens Design
Aspheric and atoric are the choices for high index
single vision lenses, especially when used with strong
prescriptions. With these designs, plus lenses lose center thickness
while minus lenses lose edge thickness. Atoric designs correct both
the sphere and cylinder parameters of the prescription giving the
best aberration control possible.
A Final Note
Remember, higher index lenses reflect light to a
greater degree. This means that they should have anti-reflective
(AR) treatment applied to them. Without it, reflections will be more
obvious and more annoying for the wearer. There are plenty of good
AR treatments on the market today, so don’t hesitate to use
one.
As more patients discover the
advantages of high index lenses, the demand for them will continue,
and manufacturers will continue to produce new, improved versions.
That’s really good news for patients and practitioners
alike.
Randall L. Smith is Director of the Opticianry
Program at Arkansas State University in Mountain Home,
AR.
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