A Brief Tour of Lenses.
Spectacle lenses come in many shapes and forms; there are hundreds of types
and styles, from many different manufacturers. We at David Kears have access
to all lenses currently available in the UK. We are therefore not tied down to
any particular product. We give the lens that is best for you, our patient,
not us.
There are two main materials used in making spectacle lenses and they are
Glass and Plastic.
Lets look at the two types of materials used for spectacle lenses, and see
the advantages and disadvantages of both.
|
Glass |
|
|
|
Plastic |
|
|
|
|
Px |
Clear |
Photochromic
Grey/Brown |
Polarised |
Px |
Clear |
Photochromic/
Transitions
Grey/Brown |
Polarised |
|
Single Vision
Bifocals
Trifocals
Varifocals |
Yes
Yes
Yes
Yes |
Yes
Yes
Yes
Yes |
|
Single Vision
Bifocals
Trifocals
Varifocals |
Yes
Yes
Yes
Yes
|
Yes
Yes
Yes
Yes
|
Yes
Yes
Yes
|
|
Advantages
On certain prescriptions a thinner lens is possible.
More scratch resistant than plastic
|
|
Disadvantages
Could be dangerous if broken.
Heavier than plastic.
Not as much choice of lens type as with plastic |
|
Advantages
Lighter than glass.
More choice of lens types.
More impact resistant than glass.
Wider range of tints available.
Can be fitted in more frames styles. |
|
Disadvantages
Can scratch easier than glass. |
|
Lens Types
Single vision: - A lens with one power/prescription
Bifocal: - A lens with two powers/prescription (Distance and Near)
Trifocal: - A lens with three powers/prescription (Distance, Near and
Intermediate)
Varifocal: - A lens with distance power at the top and changing to reading
power at the bottom with an intermediate power between the two. There are no
visible segment lines where the powers change from one to the other, as there
is with bifocals and trifocals.
Within each group of lens type, glass and plastic, different material mixes
and lens design give the possibility of flatter, thinner and lighter lenses,
which is especially useful with high prescriptions.
Coating and Tints
Lenses can be tinted or coated for cosmetic or medical purposes. These come
as full tints, graduated tint and anti-reflection coating. Choice of tints on
glass is rather limited. On plastic lenses the choice is much greater.
Anti-reflection coatings can cut down glare and make lenses more cosmetically
attractive than uncoated as well as being useful for night driving (dazzle
from car headlights)and computer work (reflections from VDU screens). Plastic lenses can have a scratch resistant coating
applied, which can help in keeping scratches to a minimum.
Photochromic
Both glass and plastic lenses are available in many lens types in
Photochromic/transitions and generally come in a grey or brown colour. You can
also have polarised lenses available in plastic.
For further information see a member of our dispensing staff, who will only
be to happy to discuss your particular requirements.
