What sort of lenses are best for me?
There are many things to consider when choosing lenses.
Should they be Plastic or Glass?
Should they be Thin or Standard?
Should they have a tint or coating or be Light-Sensitive?
Do I need Varifocals or Bifocals or Single Vision lenses?
Let’s consider each of these in more detail.
Spectacle lenses always used to be Glass. Glass is optically clear and scratch resistant. It is also heavy and can shatter.
Plastics lenses are significantly lighter than Glass. They are also shatter-resistant which means they are safer, e.g. for children or sporting activities. Some types of Plastic lens are especially strong e.g. Polycarbonate or the new PNX lens from Hoya. These, and some of the High Index materials are most suitable for rimless frames. Plastics lenses are softer than Glass and will scratch more readily. For this reason they are often supplied with a scratch-resistant coating which helps to protect the lens surface. Back to top
The thickness of a spectacle lens is dependent on the strength of the prescription and on the REFRACTIVE INDEX of the material. The stronger the lens power, the thicker it will be. Similarly the frame size plays a part. A bigger frame will result in thicker lenses and if your eyes are close together this will have a similar effect. If we increase the refractive index then a lens of the same power and size will be thinner and often lighter.
Lenses for Short-sight are thicker at the edge and thin in the middle. Lenses for Long-sight are thin at the edge and thicker in the middle.
Another way of making the lens thinner is to use an ASPHERIC lens design. This is a way of making the lens thinner by varying the curve on the lens towards the edge.
To keep your spectacle lenses as thin as possible,
- Don’t choose a frame which is too big for your face.
- Consider Hi-index lenses.
- If your lens power is positive (for long-sight) consider having your lenses specially made for the size of your frame. This sometimes costs a little extra but can make a big difference. Back to top
Tints and Coatings and Light-Sensitive lenses.
Coatings which can be applied to lenses include Scratch resistant coatings and Anti-reflection coatings. The purpose of an Anti-reflection coating is to make the lens more transparent. This has the effect of:
- Reducing the ‘glassy’ look of your lenses especially in photos
- Reducing the glare from oncoming headlights at night.
- Allowing others to see your eyes rather than your lenses.
- Helping to stop you seeing things behind you reflected in the back of your lenses.
- Improves contrast making the picture seem clearer
- Cuts reflections from the back of the lens of objects behind you which can cause distraction or glare.
Tints are often used to enhance the cosmetic appearance of spectacles but also can sometimes be clinically advisable. Ask your Optician for details.
Light-sensitive or Photochromic lenses change according to the light. They go darker in bright conditions and clearer in dull conditions (clear enough to be acceptable for night driving). Both Glass and Plastic versions are available. Back to top
Varifocals, Bifocals, Enhanced Near Vision lenses or Single Vision?
As an independent practice we are able to access the full range of lenses now available from a vast number of suppliers in order that our patients benefit from the right lens to suit their visual requirements and life style.
Varifocals, bifocals and enhanced near vision lenses are a way of having more than one lens power in the same pair of spectacles. They are normally only appropriate for people of 40 and over.
A varifocal has variable lens power to give clear vision from distant to near objects. It is good cosmetically because it looks like a single vision lens with no dividing lines, which can look ageing, and good visually because it offers a continuous range of clear focus.
It is a common misconception that varifocals can only be fitted into deep frames. With the trend towards narrower frames, manufacturers have developed a wide range of shallow varifocals to suit modern visual requirements. Not all varifocals are the same however; some are more suited to an active lifestyle, some have wider intermediate areas and are more suitable for computer users, whilst others offer wider reading areas for those who mainly require their spectacles for near vision tasks.
Freeform individualised designs are also now available; these take into account the wearer’s head and eye movements, the prescription and eye position so that the lens is tailored to the wearer, rather than the wearer having to adjust their posture to suit the lens. Such designs are available from Essilor (Ipseo), Hoya (Id), Zeiss and many other manufacturers. Our varifocals are also supplied with a non-tolerance warranty to guarantee complete satisfaction.
A bifocal also offers clear focus for distance and near but has only two distinct powers, separated by a line. The line is sometimes a nuisance either visually or cosmetically, or both. As there are only two powers in the lens, whilst distance and near vision are clear, objects in the mid-range are not clear with either power, eg computer screens, music, prices in shop windows or on the back of freezer cabinets.
Enhanced Near Vision
These lenses have been developed to take account of the visual requirements of people needing clear intermediate and near vision for the same task. Computer users need to see both a screen at arm’s length, a keyboard and reading material on the desk, which would be impossible with a single vision lens for the majority of over 40’s without altering posture or picking things up. Bank cashiers, checkout operators and numerous other occupations would benefit from enhanced near vision lenses.
Younger spectacle wearers who spend a reasonable amount of time on concentrated near vision tasks such as computer use and find their eyes are tired and aching at the end of the day may benefit from these lenses to relieve these symptoms. Back to top