TYPES OF LENSES
Single Vision Lenses
Single vision lenses are used to correct myopia (short-sightedness), hyperopia (long-sightedness) and astigmatism. These lenses have the same power throughout the entire lens and are used to correct the vision at one distance only, whether it be distance, near, or intermediate (i.e. computer screen distance) vision. They are available in numerous materials; plastic, polycarbonate, glass, photochromic (or light reactive), trivex, and are capable of having many coatings or tints that you may require.
Progressive lenses, sometimes referred to as Varifocals, no line bifocals or invisible bifocals, not only provide visual correction for the distances that traditional bifocals can't, but they also hide the fact that you are even wearing bifocal lenses because there is no visible line or segment on the lens. They provide a smooth transition from distance, through intermediate, to near with all the in between corrections included as well.
Progressive lenses tend to give the most natural vision correction compared to bifocals or trifocals. There is usually a short adaptation period when you are first fitted with your progressive lenses, where you may need to get accustomed to using them. This adaption may range from a few hours to a few weeks depending on the individual.
Nowadays progressive lenses can be fit into shallower, smaller, more fashionable frames by using progressive lens designs that are more compact. They are available in numerous materials; plastic, polycarbonate, glass, photochromic (or light reactive), trivex, and are capable of having many coatings or tints that you may require.
Bifocals are used to correct for presbyopia. The lens is divided into two segments. Normally, the upper most part is used for seeing in the distance and the lower part is for near vision.
They are usually prescribed for people over the age of 40 whose focusing ability has declined due to presbyopia. The segment for near vision correction can be shaped like a half moon, also called a flat top or a straight top, or like a round segment. Similarly to single vision and progressive lenses they are available in numerous materials.
Trifocals are similar to bifocals except that the lenses have three segments instead of two. The third segment is located between the bifocal and the distance segments and is used for viewing things in the intermediate zone, which is farther away than the near zone or about arms length away. Computer screens are an excellent example of something that is in a person's intermediate zone. Today, due to advanced progressive lens designs, trifocals are much less frequently used and are available in only a limited number of materials.
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Conventional plastic lenses, first introduced in the 1960s, have many advantages over glass lenses and are now commonly used. CR 39 plastic is used for all types of lenses. It is more lightweight and lenses made with this material don't shatter like glass lenses and are therefore much safer for the wearer. Plastic lenses can be tinted to any color and can be used to make prescription sunglasses.
Polycarbonate lenses are thinner, lighter and more impact resistant than
traditional plastic lenses.
The polycarbonate material is
manufactured differently from the way that other lens materials are
fabricated. An enormous amount of pressure is used to compress the raw
material. The resulting product holds up very well under impact, not
because it is hard and unyielding, but rather because it is flexible and
gives slightly under pressure without breaking. This extra toughness
makes them the lens of choice for children's spectacles, sports eyewear
and safety glasses.
people who require strong prescriptions, these lenses are lighter and
thinner than the standard thick 'coke bottle' lenses that may otherwise
be needed. High index lenses are 10-25% lighter and 15-30% thinner that
regular plastic, which provides a more attractive lens. They are
available in single vision, bifocal and progressive lenses.
Trivex lenses have been slowly increasing in
both popularity and availability. Trivex is the lightest of any lens
material available today. Like polycarbonate, Trivex also offers
inherent UV protection and is extremely impact resistant. Trivex is
ideal for drill mounting into the now fashionable rimless frames, the
tensile strength of Trivex makes it highly resistant to cracking around
the drill holes.Trivex is also highly recommended as the lens of choice
for childrens spectacles because of saftey.
The original type of material used for
spectacle lenses has now been almost superseded by other more beneficial
Glass lenses are usually heavy and not very safe as
they will break if dropped or impacted by flying object and they offer
no protection to the wearer. For this reason glass lenses are not often
used and are now only available at Harcourt Carter Optical as
LENS ENHANCEMENTS AND TINTS
To improve both the vision through
the lenses and the whole appearance of the glasses, an anti-reflective
coating (also called AR coating) can be applied to the lenses. AR
coatings make the lenses clearer to look at and through.
They consist of several layers of metal oxides
applied to the front or back lens surfaces. Because of the layering
effect, AR coatings sometimes have a hint of green or purplee colourr,
depending on the individual manufacturer's formula. Each layer is
scientifically calculated to block reflected light. The result is that
you'll see a reduction in glare, annoying reflections and halos around
lights while wearing the lenses. This is a great safety benefit when
you're driving at night.
The results in a reduction in glare, annoying reflections and halos around
lights while wearing the lenses. This is a great safety benefit when
you're driving at night.
Anti-reflective coating reduces both
internal and external reflections on the lenses themselves, creating a
nicer cosmetic appearance. Internal reflections appear, as rings that
make lenses look thick. External reflections mask your eyes from a
clear, complete view when someone is looking at you. So with an
anti-reflective coating, lenses appear thin or non-existent, and your
eyes look more natural.
Anyone on TV or whose photo is taken
often benefits tremendously from the better appearance of AR coated
lenses, but really, all eyeglass wearers would benefit from an
anti-reflective coating from a cosmetic point of view. If you have a
strong prescription, you can use the AR coating in conjunction with
high-index or thinner lenses to make your glasses look and feel as thin
lenses are used for prescription sunglasses. Polarised filters are made
of a chemical film applied to a transparent plastic or glass surface.
The chemical compound used will be composed of molecules that naturally
align in parallel relation to one another. When applied uniformly to the
lens, the molecules create a microscopic filter that absorbs any light
matching their alignment.
Most of the glare that causes you to
wear sunglasses comes from reflection off of horizontal surfaces, such
as water or a highway. When light strikes a surface, the reflected light
waves are polarized to match the angle of that surface. So, a highly
reflective horizontal surface, such as a lake or the sea, will produce a
lot of horizontally polarized light. The polarized lenses in sunglasses
are fixed at an angle that only allows vertically polarized light to
enter the eye hence reducing the glare.
Photochromic lenses are lenses that change from clear to dark when you go into the sun. The brighter the sun, the darker they get; getting as dark as sunglasses in bright glaring light. Photochromic lenses are suitable for indoor and outdoor use as well as for use at night. They are available in a variety of colours including Grey, Brown, Green, Blue and Extra Grey/XTRActive. Most importantly, photochromic lenses block 100% UVA & UVB radiation. At Harcourt Carter Optical we retail only the best photochromic lenses available on the market in Zeiss PhotoFusion and Transitions lenses.
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Ultraviolet (UV) exposure is damaging to the eye and eyelids and can contribute to the formation of cataract, pterygium, macular degeneration and other eye problems. For this reason blocking UV with your lenses is very important. UV treatment of lenses provides protection from both UVA and UVB and does not change the appearance of your lenses. At Harcourt Carter Optical, we use mainly Zeiss lenses to protect your eyes. All Zeiss lenses, even the clear ones, have 100% UV protection as standard. Additionally, all photochromic and polarized lenses provide 100% UV protection. In lenses where UV protection is not a standard feature, UV protection can be added in a simple process to provide that extra peace of mind that you are protecting your eye health.
Tints are available for plastic lenses and can be had in a variety of colours. Lighter fashion tints are used
primarily for cosmetic purposes to enhance the wearer's looks. Darker
tints allow the wearer to use the lenses as sunglasses. A tint can be
solid, where the entire lens is tinted the same color, or gradient,
which is a graded fade from dark to lighter usually fading from top
down. We can also provide a mirror coating on any prescription