Part Six: Choosing The Right Lenses For You!

With literally thousands of products on the market, from thousands of manufacturers and suppliers worldwide, you might be forgiven for being a little confused when it comes to selecting lenses. But don't worry, here at Glasses4Less we have sourced and 'filtered' the products for you from the world's top suppliers and manufacturers in the optical industry. Whether you spend £20 or £200 you can be sure that you are getting the finest quality and value for money pound per pound spent.

To help our customers with their decision making we have grouped our lens products into three simple categories.

STANDARD

PREMIUM

ELITE

The first thing to understand is that ALL lenses are classed as medical devices and that the entire field of spectacle manufacturing, in particular spectacle lens production depends on consistent adherence to standards. The difference between standard, premium and elite lenses can be compared to the difference between motor vehicles. Take the new Mercedes-Benz SL55 AMG Roadster and the Ford Ka, both get you from A to B, both comply with all the relevant safety standards. However I think we all understand that the Mercedes-Benz SL55 AMG Roadster is an Elite product and just that little bit special. The same applies to lenses. They all do the same job, however some out perform others by design.

Lenses can be made in two basic materials Plastic (Organic) or Glass (Mineral).
The majority of the lenses sold today are made from Plastic, they are lighter and safer than glass and with new materials, coatings and emerging technologies they are getting thinner.

High Index Lenses

Each lens has a "Refractive index", the higher the refractive index the thinner the lens. Standard plastic stock starts at n=1.502 index, below is a list of some of the standard, mid and high indexes available, remember, the higher the number the thinner the lens:

n=1.50, n=1.56, n=1.59, n=1.6, n=1.61, n=1.69, n=1.74, n=1.8, n=1.9

Now for the science bit for those who are interested!
The refractive index of a lens is obtained by:

Refractive index n = Speed of light in Air / Speed of light in Medium

The way in which the refractive index is calculated is not important to you the customer. What is important is what it means to the thickness of the lens. The highest refractive index currently available in Plastic is n=1.74, however I predict that it will not to be long before we see n=1.8 or even n=1.9 index on the market. Currently super high index lenses of n=1.8, 1.9 are only available in glass. It is worth remembering that whilst plastic lenses may scratch easier than glass they rarely break and when they do crack they crack "safer" without shards or splints associated with glass lenses.

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Lens Extras - Other Lens Options - Thin Lens Calculation

Most people think that by simply throwing money at the highest index lens will get them the thinnest job possible. This is not always the case. Proper frame selection with regard to size, shape and fit can make a world of difference to lens thickness as can Thin Lens Calculation for + or positive prescriptions. Simply put, this just means that the lens is made no bigger than absolutely necessary to fit the frame with the optical centre of the lens correctly aligned with your own P.D. With + or positive prescriptions, inappropriate, over sized lenses can look excessively thick and unsightly. If you combine this service with a high index lens you can achieve the thinnest lens possible for your prescription/frame combination. All the prices on our website are for STOCK diameter, uncut lenses; however we do offer Thin Lens Calculation as a Lens Extra. Simply contact us for further details.


We have seen that the higher the refractive index number the thinner the lens will be. This is because of the type of lens materials used in the production of the lens. Materials that bend light more than others have a higher refractive index and hence a shorter or longer focal length. The result is that the same lens power and focal length can be achieved from less lens (material) making them thinner. Like most things in life they these gains come at a price (and not just ££'s). The down side is that high index lenses are usually slightly heavier, especially glass lenses. Also the materials used to produce high index lenses dramatically increase surface and internal reflections. Thankfully the recent technological advances in the development of anti-reflection, multi coatings have largely overcome this problem. Nearly all high index lenses these days come with reflection free multi coatings as standard. In fact, due to the softer nature of high index plastic, if it wasn't for these coatings, which now contain a hard coat layer as standard, many high index lenses wouldn't be available.

Lens Options.

Standard Plastic CR39 1.5
These are the type of lenses included with the frames on our website. They are Ideal for most prescriptions; however prescriptions with powers stronger than +/-3.00 would start to benefit from a higher index lens.

Mid Index Plastic 1.56
These lenses are up to 20 percent thinner than standard CR39 and 23 percent lighter. Hard coated as standard they give good resistance to scratching and abrasion, thinner, lighter and flatter than n=1.5 index.

Mid Index Polycarbonate 1.59
These lenses are up to 10 times stronger than standard plastic and are fitted as standard to all our rimless frames as they are an ideal choice. Up to 20 percent thinner and 30 percent lighter than standard plastic. One hundred percent UVA and UVB protection

High Index Plastic 1.6
These lenses are an ideal option for prescriptions of up to +/-5.00. They are supplied with a Hard Multi Anti-Reflective coating as standard (HMAR) which will reduce glare in situations such as night driving. 1.6 lenses are 23% thinner than standard plastic.

High Index Plastic 1.67
This is a very affordable high index lens, ideal for supra or rimless glazing if you are looking for something thinner than 1.59 index. These lenses 15 percent thinner than the1.6 index and 25 percent flatter. Ideal for prescriptions of +/ -7.00, beyond this range will start to look thick.

Very High Index Plastic 1.74
This is the thinnest and the most expensive plastic lens available on the market today. It is 50 percent thinner than the 1.56, 15 percent thinner and 25 percent flatter than 1.6 index lenses and 30 percent lighter than the glass equivalent. This is the ultimate plastic lens, great for mid to high prescriptions, provides full UVA and UVB protection.

Very High Index Glass 1.8 and 1.9
Prescriptions that may require such a very high index are beyond the scope of this internet site.

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Lens Types

Just to confuse you further, there are also hundreds of different styles of lenses available. Thankfully the industry tends to stick to a dozen or so standard forms and the majority are considered "specials". It makes sense to make your selection from standard designs when it comes to lens types as "one off" or occupational designs can be expensive. Anything is possible but inevitably it comes with a price tag!

Single Vision Lenses
As the name would suggest, these are lenses for single vision correction e.g., distance intermediate or reading correction. If you need a distance and reading correction you could potentially find yourself with up to three pairs of spectacles. A pair of spectacles for distance use, reading and an intermediate pair for the computer or office. Single vision lenses are usually the cheap option however; based on the amount of customers we get who lose or break their multiple pairs of spectacles I'm not so sure. Spectacles that are on your face rarely get lost of broken, (there are exceptions) but the poor reading glasses get a real hard time.
Single vision lenses are available in both plastic and glass and all refractive indexes.

Bifocals Lenses
Bifocals are basically distance glasses with a reading segment fused or molded into the bottom of the lens. Bifocals are simply distance lenses with a reading segment and un-like Varifocals have no intermediate correction. There are various types or "shapes" of the reading segment available.

The "D" Seg
The standard segment shape as offered on our website is called, for obvious reasons, the "D Seg" this looks like the letter D on its side with the flat edge at the top, hence the name D Seg. This segment comes in various sizes, D22, 25, 28, 30, 35, 40, 45 millimetre. The standard segment size on the website is D28 (28mm)

The "Round" Seg
Another standard segment shape is the round segment. This is simply a round button or segment, fused or molded into a distance lens during the manufacturing process. It comes in the following sizes R22, 24, 25, 28, 38, 40, 45 millimetre. The standard segment sizes are either R25 or R28.

Executive
Another type of bifocal called an executive or "E Type" bifocal is also available. With this lens the lens is basically divided into two halves with the whole bottom half of the lens dedicated to near vision. This lens is not as popular as it used to be, some people find that the reflections on the dividing line can be quite annoying, however it is a great occupational lens for people who read a lot.

Bifocals are available in standard plastic, 1.6 plastic, Transitions Brown & Grey, standard glass, Photo Brown and Photo Grey Extra.

Varifocals
Varifocals correct distance, intermediate and reading prescriptions all in one pair of glasses. Varifocals are more complicated than standard single vision or bifocal lenses, not only do they need fitting to your correct P.D but they also need to be set at the correct vertical height from the centre of your pupils to the lower rim of the frame.
If you require a simple re-glaze of your existing spectacle frame with new Varifocals then this is no problem. We simply set your new lenses to your existing measurements.

What is important is that you experienced no difficulties using the existing Varifocals that you send to us for re-glazing. This is because if the non-tolerance problem was due to a fitting error then we would be simply copying this error as we have no way of cross checking for the correct fit.

If you would like a new pair of frames fitted with Varifocal lenses then please contact us directly. We only accept these jobs subject to our approval. Whilst it is not impossible to achieve, it requires more work and effort from both parties to make sure we are both happy before we proceed. The Varifocals that we have supplied to customers have been a huge success, however it is a time consuming process that some customers would rather not get involved with. The upside is that you can save a fortune compared to high street prices. If you are considering Varifocals you may want to consider the following first.

1. The first step is for us to see your prescription and assess suitability.

2. Next we need to make sure we have a good fitting frame. This may take a while as various frames are posted back and forth on approval. Sending us an existing pair of spectacles can speed up the process and help us to advise you regarding your frame selection. It will also provide us with your P.D measurement.

3. Once you are happy with the frame we will mark it up for you with your P.D measurement. We will also, using our experience based on the information we have to hand about you, mark the lenses where we think the fitting cross position should be.

4. We will then post the marked up frame to you for you to cross check our measurements. Again, if this isn't right the first time, this may need posting back and forth until it is correct. Only once we are both happy will we proceed with the order.

5. If you have never worn Varifocals before we advise you to get them from your local optician. After reading the above, if you still wish to buy on-line then please give us a call. We Guarantee all our Varifocals and will exchange them for single vision lenses or bifocals if you find you cannot get on with them for some reason.

Lifestyle Lenses

Computer Lenses

Now there is a completely new lens that will come as a great relief to many computer users. This new development comes from Essilor ®, the people who invented varifocal lenses. This is an exciting new lens and has been a huge success for us. The lens is called Varilux® Computer and if you are one of the few people who can't adapt to varifocals let me assure you that these are occupational lenses specifically designed for the computer user. We have successfully supplied these lenses to customers who cannot adapt to varifocals, they are simply fantastic! They can not be worn for general use such as driving. Two lens types are available for two types of computer user. Computer 2 Visions (2V) and Computer 3 Visions (3V) which refers to the wearers viewing distances.

Computer 2V ~ is designed for people who work on the computer for long periods, often alone, sometimes concentrating very intensely. Their focus may shift between, computer screen, keyboard, notes, graphics and text. Computer 2V gives full coverage of keyboard and screen however once the task is completed the spectacles would need to be removed as distance vision will be blurred.

Computer 3V ~ is designed for people who work on reception, in open plan offices or in conference rooms where there is more interaction with people or objects. They are designed for repeated shifts between near to semi-distance vision, ideal for the computer user who interacts frequently with their surroundings.

Unlike varifocals, no vertical fitting height measurement is required. The lenses are centred at your near P.D on the horizontal centre line (HCL) of the frame. The frame needs to have a minimum overall depth of 30mm. Please contact us for further details.

InterView Lenses

Another Essilor ® product to help you rediscover your mid or intermediate vision. Reading glasses limit your visual focus to two or three feet or less and everything beyond that becomes blurred! InterView lenses combine your reading prescription with your mid vision or intermediate prescription in one single lens.

InterView is the ideal lens choice for office work, using a computer, having a meal, playing chess or cards for example. They do not offer a distance correction and are not suitable for driving.

Please contact us for further details.

Complex Prescription and the limitations of internet shopping.

Unfortunately there are limits to what is possible without seeing customers in person. Unless specially agreed with our supervising optician, Glasses4Less will only supply spectacles with lenses of a spherical power between +8.00 and -8.00 (dioptres) and a cylindrical power between +4.00 and -4.00 (dioptres). We reserve the right not to accept any order that we feel is going to be unsuitable. As prescriptions become more complex a greater degree of accuracy required. For example: A +10.00 lens set with 1mm of error would cause a one prism error. A +1.00 lens would need to be set with 1cm (10mm) of error to achieve the same degree of prismatic error. Just because your prescription is within our range doesn't necessarily mean we will supply it. If our supervising optician believes that it is in your best interest that you see an optician in person your order will not be accepted.

Orders for multifocals (bifocals or varifocals) will not be accepted where the reading addition exceeds +3.50 or is less than +0.75 dioptres.

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