In all my years of wearing glasses, I have never heard about super thin lenses or the term 'high index lenses' as it is also called.
In my last blog post, Do lightweight glasses exist, I weighed all my glasses to compare my old, heavier plastic frames to my new lightweight TR90 plastic frames. But modern prescription lenses also contributes to making eye glasses lighter. Lets explore further.
Optics and lens technology are very complex fields so I'm going to try to explain in simple terms and not go too deep into the technical details.
What are lenses made of?
CR-39 plastic is the most widely used lens material as it's easy to clean, scratch resistant, and offer 100% UV protection. An even more high quality material used to make super thin lenses is Polycarbonate Plastic (PC) which makes the lenses more lightweight and impact resistant than CR-39 lenses. Because of this, polycarbonate plastic is used to make sports goggles and safety glasses. Since polycarbonate lenses are more prone to scratches, Digby Duke's lenses always comes with anti-scratch treatment on them.
Artistic photo of our Kaiser Steel frames.
So what does high index mean?
Lenses for correcting nearsightedness (myopia) or farsightedness (hyperopia) do this by bending light as it passes through the lens. In technical terms this is called refracting the light. Your eye prescription will tell how much lens strength you need to correct your vision and it is measured in Diopters (D). Mild nearsightedness is below -3 Diopters and more than -6 Diopters is considered very nearsighted.
The higher the refractive index of the material, the less curvature is needed to be ground on the inside of the lens to create an eye prescription. Meaning simply that a high index lens can bend light more efficiently without being as thick.
1.6 or above is considered high index.
So if a normal thickness lens has a refractive index of 1.5, then a high index lens of 1.60 will be about 25% thinner. A 1.67 index lens is 40% thinner than a 1.5 index lens and a 1.70 index lens is 50% thinner. The thinnest you can get is a 1.90 index lens which is 75% thinner and is classified as a very high index lens.
If you'd like to dig deeper, you can read more about corrective lenses here: http://en.wikipedia.org/wiki/Corrective_lens
Does your eye sight decide how thin the lenses can or can't be?
If you are strongly nearsighted, farsighted or have astigmatism, super thin high index lenses are definitely recommended. For example, when you are nearsighted, the lens has to be thin in the middle and thicker towards the edge of the lens. Therefore, the more nearsighted you are, the thicker the edges of the lens are. This can make glasses heavier and have an unwanted cosmetic effect, if you'd like to wear thin rimmed glasses and the rim is thinner than the edge of the lenses.
Farsighted lenses are thicker in the middle and thinner at the edge.
Kera Darling frames
On a personal note:
I have astigmatism and have always been told by optometrists that I therefore can not wear rimless or half-rimmed glasses because the lenses are too thick. What a lie! They just couldn't offer me thinner high index lenses because of the ridiculous prices they charge! It would make my glasses even MORE expensive.
Here in Norway they charge about USD $350 per lens for high quality progressive lenses. And we're talking for ONE lens alone! No wonder prices for a pair of progressive glasses quickly reaches $1500!
Thank GOD I started Digby Duke before I got to the age where I need progressive glasses. Which could be any day now that I'm 43. But I definitely know where I'm going to get my future glasses from (Can you guess?) and I'm certainly NOT paying $1500 or even $200 for them.
So what is the index and lens material of Digby Duke's super thin lenses?
Our standard lenses are super thin 1.67 CR-39 plastic lenses. You can also upgrade to REALLY super thin 1.74 lenses but this is not necessary unless your eye prescription is higher than - 6 in the distance part of the lens.
We make glasses for eye prescriptions between -10/ +6 SPH. If you also have astigmatism, we can make glasses for CYL values up to +/ -6.
The reason we use CR-39 plastic for lenses that are thinner than the 1.6 index ones is that it is difficult to manufacture polycarbonate lenses with indexes higher than this. So one has to resort back to using the plastic called CR-39. But that said, our lenses are still of the highest quality both in terms of vision and thinness. They sit well in the frame and contributes to making Digby Duke glasses comfortable and attractive to wear.
Kaiser Jet Shiny and Kaiser Jet Matte
Anything else you should know when choosing lenses?
Many other online prescription glasses stores have complicated ordering menus where you have to pick what type of lenses you want, lens material, index etc. Without an optometrist or optician at your side to guide you, this could make it both confusing and difficult to buy your glasses online.
This is why we here at Digby Duke only offer the very best super thin lenses for everyone no matter which frame you choose or what your eye prescription is. You don't have to pay extra for thinner lenses or lens treatments which means you don't have to spend time and energy picking from a confusing menu.
With us you are guaranteed that your glasses will come with the absolute best and thinnest lenses possible with all the special lens treatments included such as 100% UV protection, anti-scratch, anti-fog, and anti-reflective treatments.
All you need to decide on in terms of lenses is whether you want clear, tinted or transition lenses. In case you don't know what transition lenses are, they are clear when you are inside and turn brown like sunglasses when they come into contact with UV light.
Buying new glasses should be an enjoyable experience. We hope that by making the order process as simple as possible and offering all the best in a single, affordable price and free worldwide shipping, you can spend your time having fun looking at different frames and trying them on with our virtual try on tool instead of worrying about technical lens details.
And should you still find it difficult, email us at email@example.com and we'll help you out any way we can.