Digital Lenses: A Deep Dive

Below, we share with you how free-form lenses (also called digital high-definition lenses) are made, how the fabrication process begins starting with a eyeglasses prescription to how it is optimized to create crisper vision.  The key component to digital lenses is the precision of the software-controlled equipment that is used to surface the lenses compared to conventional tools.  For example, the free-form instruments used today can surface lenses in power increments of 0.01 diopter (D), compared with 0.125 to 0.25 D increments of conventional eyeglass lens tooling.  The fabrication of digital, free-form lenses takes into account how the lenses are positioned in front of the wearer's eyes to provide the most accurate lens power and the sharpest vision possible.

Step 1:  Prepare the Digital Lens for Surfacing. 

As mentioned prior, digital lenses are different from standard lenses by the way they are processed.  Standard lenses are prepared by attaching a device, called a block, to the back of the lens.  Digital lenses are different, they are blocked from the front of the lens.  Why are they blocked from the front? It is because the lens is already semi-finished with the optical power on the front of the lens. This is the exact opposite for standard lenses, the optical power is on the back of the lens. See below for why this is important. 

Step 2:  The Digital Lens is Surfaced.

Surfacing is the key difference between digital and standard lenses. The process of digital lenses being surfaced on the backside of the lens is called a free-formlens.  Free form surfacing is the process of using a diamond edge grinding tool that can take into account over 10,000 different surfacing processes during production.  Why is this important?    If the Optometrist was using digital equipment, then the glasses prescription they provide you will be written for digital lenses.  Free form technology used during surfacing is extremely advanced and is one reason why the costs are increased for digital lenses.  The free form process uses a very precise computer controlled diamond cutting tool that can move in 5 different vectors, called a 5-Axis instrument.  This is important because it enables the machine to cut your exact prescription, which takes into account all the factors your Optometrist prescribed.  Standard lenses can not take all of those factors into account due to the machines they are processed on. 

Step 3:  The Digital Lens is Polished. 

The process of polishing is to smooth out the diamond cutting marks that were left during surfacing.  The polishing process removes 10's of thousands of an inch, or 0.0001 of an inch, to create an extremely smooth surface.  This is where things get interesting.  Even though the lens has been surfaced on the back, the optical properties on the front of the lens have not changed.  The surfacing and polishing have removed lens material in a very specific way so you do not see any aberrations.  We talk more about aberrations below. 

Step 4:  The Digital Lens is Cleaned.

While cleaning sounds like a simple step, it is not.  First, the block on the back has to be removed from the lens carefully not to scratch the lens, remember at this point, there are no coatings to prevent scratches.  This is performed by using hot water to melt off the block.  Keep in mind the water being used in this process is ultra-pure, known as deionized water.  After the lens is gently rinsed with soap, it is again rinsed with deionized water and dried in preparation for the next step. 

Step 5:  The Digital Lens is Tinted.

Not all digital lenses are tinted, but if you requested tint from your Optometrist, like a silver flash mirror or a dark brown tint for your sunglasses, this is the step where the lens is dipped into the appropriate bath using proprietary metal-oxides to achieve the desired color and tint. 

Step 6:  The Digital Lens is Coated!

For us a consumers, this is a very important step and other than the prescription, one we notice the most.  At this point during the production of the digital lens, the anti-scratch and anti-glare (AR) coatings are going to be placed on the lens.  It may not be what you think and it is also why you have to wait longer for your glasses.  The anti-glare and anti-scratch coatings are placed on the lens using a process called vapor deposition.  A vapor deposition coating, VCD, uses a proprietary liquid that evaporates under high vacuum and intense pressure and morphs into a gaseous phase.  This gaseous phase is then transported over to the 80+ lenses and is deposited onto the lens which turns into a solid phase and bonds to the plastic substrate.  Some manufactures actually match the digital lens, by fuctionalizing it with another chemical, and matching the coating to that chemical to ensure exceptional stability.  Have you ever seen a coating come off lens...it was not substrate matched. Vapor deposition technology provides good impact strength, excellent abrasion resistance and are so durable that protective topcoats are almost never necessary.  This is the reason that top of the line anti-glare coatings are over $100.  You truly get what you pay for in this department. 

Step 7:  The Digital Lens is Inspected.

At this point in the process, the digital lens is inspected for any imperfections such as dust or was it damaged during surfacing process.  Damage or a quality control failure can happen, although rare, it does cause a delay in the customers glasses. The digital lens is then checked to ensure to correct diopters, axis, cylinder, thickness, design and diameter.  Lastly, before it is stamped with a seal of approval, a mechanical safety test is performed to ensure it passes safety standards.  This process is the same for standard lenses as well. 

Step 8:  Frame Measurements.

We are getting close to the end of making the digital lens.  The next step is to cut the lenses so they will fit snuggly into your frame that you picked out.  Your frame is now placed into a machine that traces the inside of the bezel, which is what holds your lens in place.  The computer traces your bezel and sends that information over to the machine that cuts the lens. 

Step 9:  Last step! Cut Your Digital Lenses.

The last step in the lens making process is to grind down the edges so they fit into your frame that you picked out.  Think about how many millions of different frames are out in the world.  A computer can not remember all those shapes and minor variations that happen during the frame manufacturing processes, which is why tracing is so important.  Every lab traces your frame so it can ensure the lens is custom cut for that frame, and that frame only.  Can this lens be placed in two of the same frame, of course, but one may be more loose than another.  After the lens is cut, a technician inserts the lens into your frame and you now have a complete pair of glasses!

To recap, the Optometrist acquired digital readings factoring in frame fitting position, prescription, vertex distance, pantoscopic tilt, pupillary distance, and eye movement patterns and many more during your eye exam.  All part of your prescription that was sent with your frame to lens laboratory, who then translated those measurements into a digital free form lens that was placed in a frame of your choice.  It has arrived and your try them on for the first time.  What should you expect from a digital lens?

The result is that high-definition free form lenses provide the widest fields of view and in many cases edge to edge clarity.  They provide much sharper image quality and superior peripheral vision as well as improve your ability to distinguish subtle differences in light vs dark situations.  When one has the need for a progressive lens and a digital lens is chosen, it becomes an astounding difference.  We here this everyday, the customer says "WOW!" I have never seen so clearly in my life.  How is this possible you ask?  Other than the advanced plastics, superior coatings, and 5-axis back-side surfacing, the answer is aberrations.  Aberrations are in simple terms are imperfections in the visual system that cause light rays to be improperly focused.  At night, is when it can be at its worst.  Especially, when it is dark and rainy it will be most prominent. 

Above, you are seeing actual aberrations, or imperfections, in a patients eye.  Think of the pictures as topologcgial maps of the eye, like mountain ranges, just on a small scale.  We all have small imperfections and we now have the tools to analyze and correct for these small perfections.  This is why digital lenses are becoming so popular.  As you can see, it is important to have the right technology in order to be able to measure these small imperfections.  

Below are the instruments that Tradewinds uses to detect and determine what kind of aberrations someone has.  There are over 100+ different aberration variations! 

Virtually anyone who wears eyeglasses is a good candidate for free form (high definition) digital lenses.  Individuals with higher prescriptions will notice greater benefits than people with only mild prescriptions because higher the prescription, the more severe the aberration.  Again, one of the best indicators that high-definition lenses might be a good choice for you is if your Optometrists says you have healthy eyes and 20/20 vision, but you are bothered by glare or your vision seems indistinct.  If you are dissatisfied with the clarity of your eyesight with your current glasses, ask your eye care professional if high-definition eyeglass lenses might provide sharper vision.

Below, you will learn the differences between progressive lenses.  Above details how computer technology is involved in manufacturing a pair of lenses.  We are lucky today that computers and advanced technology have made adjusting to PAL technology easier than ever and for existing PAL wearers, technology has made major break-thoughts in how to grind and polish lenses for a much better experience. 

They’re are two important factors that have to happen prior to having a pair of PAL lenses made.  First, the Optometrist needs to provide and accurate prescription for visual lifestyle.  Lets say that again, your visual lifestyle.  If you are an outdoors man and never tend to look at a computer then your PAL will reflect that lifestyle.  If you are a truck driver and spend a lot of time on the road looking at the dash of your rig and looking into the distance, the PAL lens will reflect that as well.  If you spend a majority of your day looking at the computer, again, your PAL will reflect that need too.   Lets think about that for a moment.  The distances for all of those are different and require a different power to be cut into the lens.  Those different distances are represented in a PAL in 3 separate areas of the lens.  Distance, Intermediate and Near.  This is one important reason the Optometrist asks about your lifestyle and how you use your glasses on a daily basis. 

The next important factor is taking accurate measurements with a specific frame that reflects your current lifestyle.  Okay, we have reviewed distance, where PALs can help from a few inches to hundreds of yards away.  But remember, glasses lenses are a three-dimensional product and many various measurements can affect the way you actually see out of a pair of lenses.  See the list of measurements below that are factored into making sure you can see out of your pair of glasses when you put them on. 

-   Back Vertex Distance

-   A & B measurements

-   Pantoscopic Tilt/Angle

-   Segment Height

-   Frame Wrap 

-   Cylinder in Prescription (Rx)

-   Astigmatism

-   Thickness of the Lenses

-   Digital or Standard Lenses

-   Patients pPosture

If any one of these measurements are off even by a little, your adjustment into a PAL lenses is going to much harder than it would be if they were correct.  It is mostly science, but the human factor also plays an important part, as computers and measuring tools cannot know if you do not like the way your frame feels on your face or that you are having eye pain or headaches because your pantoscopic tilt is not enough.  No matter where you purchase your PAL lenses, remember there is an adjustment period and here are our 10 tips to adjust to your new PAL lenses.  It takes time and practice and it is not an instant adjustment.  Keep practicing, you will get it!  If not, go back and see your Optometrist, one of the measurements above may need to be adjusted. 

It is important to realize that it takes a talented team of Opticians and Optometrists to get a PAL prescription (Rx), measurements, frame adjustment, and lens selection correct for a patient to be able to adapt quickly to their new lifestyle lens.  What do we mean when we say adapt?  The way you move your eyes, neck and body will begin to adjust from wearing a single vision lens.  These muscles are not use to moving this way and can cause soreness and may be uncomfortable.  This will take place with all PAL lenses not matter where you make your purchase.  This is called the adjustment period and can take up to 5-10 days.  We have described what goes into making the lens properly, but we still have to choose which lens works best for your lifestyle.  There are hundreds of different PAL lenses. It is actually overwhelming when one starts to list out every single lens from every single lens manufacture. This brings us to our next segment...

Today, we have more PAL options than ever, PAL lenses are like golf clubs.  There is a lens for every specific person and their particular lifestyle.  So as you can imagine, depending on the measurements that are taken and submitted to the lab greatly affect the results of the PAL lens, which greatly affect how much you will have to move your neck, back, eyes and body.  The three top manufactures of PAL lenses are Zeiss, Essilor and Hoya.  A newcomer to the pack is Shamir which also makes excellent lenses.  As a matter of fact every. single. one of these companies makes an excellent product.  They are all working on a PAL that works for everything!  And Yes!  These companies are getting closer to creating a lens that works for patients in all situations only requiring a single pair of glasses.  Wouldn’t that be nice!  No need for your golfing PALs, driving PALs, working space PALs, boating PALs, etc.  While they are close, these companies have not quite figured it out yet.  So in the meantime, they all offer a good, better, best PAL product for patients needs.  When combined with very specific measurements, the PAL becomes a very custom product.  What does Good, Better Best look like in the world of PALs?

As you can see above, the Good PAL lens in on the left and moves to the Better lens and finally the Best lens is shown on the right.  At first glance, the difference does not appear to be that great, however, lets take a look at the distance part of the lens (top).  Each of the top 3 manufactures above will flatten out the visual space in the distance area as the lens moves toward the right to the Best.  Seems minor, but your neck will thank you in the long run as it will keep you from having to turn your neck further to the left or right to have a particular object in focus.  The intermediate (middle) part of the lens is the next most important feature of the lens and one that affects most patients.  The intermediate space in the lens is where you will look at your computer, dash board, and any other times in that distance range.  Take note of the how the area opens up as you move to a more premium lens.  The standard, or Good, lens is so frustrating when coming from a single vision lens and trying to learn a PAL because of the constant neck turning required to achieve what you were use to in a single vision lens.  And finally is the reading portion, or bottom space, of the lens.  This is where you will read your cell phone, newspaper (is that still a thing?), type on on iPad, etc.  The same issue with the intermediate space occurs on the economical lens, there is just limited space to visually see what you are doing so it requires a lot of neck, head and eye movements, which get very old after day one.

What we are discussing is the corridor of the PAL lens.  When all the technology, measurement and calculations are taken into account, it is the corridor that is created and is ultimately the PAL lens.  The corridor does not have the same thickness as it moves from top to the bottom of the lenes, it changes.  There is a calculated gradient that is ground into the lens and then polished (as shown above).  What creates a perfect corridor and why is that important?  Three important factors are needed to have a perfect corridor.  First, is the right technology, the lens absolutely has to be digital lens, which means it is surfaced from the back of the lens and not the front.  Next, all of the digital measurements need to be taken mentioned above plus a few others. Last, the lens itself needs to be a high quality polymer that is clear and passes internal quality controls of a company that has good manufacturing processes (GMP).  The top three companies have made the investments for the latest in technology for speed and precision.  All of these factors have led us to the most important part of a PAL lens: Asmooth corridor.  Creating a smooth corridor is not an easy task and requires heavy investment in technology and understanding the science of polymers and optics.  A smooth corridor allows for the patient to seamlessly transition from distance to their intermediate to their near distance without ever seeing a line or having a wavy effect.

Photo Credits: Zeiss, Review of Optometry, Springer Link, Phsy.org, and Marco Ophthalmic.