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PostPosted: Tue Mar 21, 2017 3:41 pm 
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Herein is what I consider to be the seven deadly sins of shopping mall opticians. I ain't no doctor, so don't trust your eyes on what I have to say. Just bear in mind that the doctor who examines your eyes is an ophthalmologist. The bubble-headed blonde who sells you UV coatings is an optician. If you find any inaccuracies on this page, be sure to contact me and let me know.


I have no sympathy for opticians. Here is a collection of things you will never hear one say, "You only need to replace one lens, so you don't need a complete set of glasses," or "I see you have a broken frame. I can order you a replacement part for you if I don't have a spare for you," or "Here are some lens coating options which you do not really need, but it couldn't hurt," or "How can I give you a pair of quality eyeglasses while saving you the most amount of money?"

Here's the deal. An optometrist will strive to give you 20/20 vision. Just what the heck is "20/20" anyway? In 1862, a man named Snellen devised a testing system to determine people's eyesight. He asked people to stand at 20 feet and through experimentation discovered the smallest sized letter that most people with good eyesight could see. He called this a size 20 letter and the vision was recorded as 20/20 e.g. at 20 feet, you can read line 5. At 40 feet you can read line 2. If you are nearsighted, you might only be able to read line 2 at 20 feet, so your vision would be 20/40. This is far from good science.

We are all comparing our eyes to bunch of "normal" people tested by Snellen in 1862 in a rather dubious fashion. If we do not have as good eyesight as these "normal" people, we spackle some lenses in front of our eyes. I say, if 63% of the population need eyeglasses to make their vision "normal," then we need to change the definition of "normal eyesight!"

As I get older, I tend to be less likely to be pushed around. In Walmart, I hear rumored that opticians wear buttons which say, "If I do not ask you about AR (Anti-Reflective) coating then your eyeglasses are free!" Of course they will want to ask you about something which typically costs $80 for a thin film coating. AR coating removes most reflections by phasing light 180 degrees. The problem is that the coating has to be exactly 1/2 of the wavelength of white light, measured in billionths of a meter in thickness, prone to wear and scratches. After six months, AR coating anomalies may become more annoying than the reflections, prompting a never-ending cycle of buying a new pair of glasses.

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Scam #1 - Anti-reflective coating. AR coating is expensive, should be done by a reputable lab, and will require careful cleaning to prevent damage. Plastic and glass lenses do not need AR coating (in my opinion). Polycarbonate and high-index lenses are more prone to unwanted reflections. Labs make a lot of money on AR coating; ask them to knock 25% off, else you will pass on this option. Some labs "accidently" apply a crappy AR coating, which will begin to peel off in 1 or 2 years. This may be done on purpose to force you purchase new eyeglasses.


If you did not ask for AR coating, ask them to remake your eyeglasses without it. This is the new number 1 scam. Some labs (notably Lenscrafters) will apply a crappy AR coating which will peel off, crack, and become annoying enough to force you into buying new lenses. Of course, if you ask for new lenses, they will talk you into buying a complete set of eyeglasses. They will warranty the AR coating "for the life of the prescription." Prescription life is less than two years. These labs want a way to force you to buy new eyeglasses every two years. AR coating fits the bill. If you are seriously looking into AR coating, check out Crizal Technology. Crizal is an AR coating which is chemically bonded to the lens, no just coated on - or so they say. I tried to purchase eyeglasses with Crizal Technology, but the lab screwed up the coating twice. I gave up on AR coating.

There is UV (anti-Ultraviolet light) coating. Ordinary optical glass filters about 84% UV. Most premium eyeglass lenses filter over 90% of UV. CR-39 plastic filters about 95-98% of UV. Polycarbonate filters over 98% of UV. I concede that filtering UV light is a very good thing, but few people realize that nearly all automobile glass already filters it. Unless you spend a lot of time outdoors, (in my opinion) you don't need UV coating for anything other than glass lenses. If you think you need it, put the UV coating on your sunglasses, not your eyeglasses. UV coating turns perfectly water-white optical lenses into dingy yellow ugly things which you'll have to live with for a long time. The source of most unwanted UV radiation comes from the reflection of the inside of your eyeglasses, not from UV light passing through the lenses.

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Scam #2 - UV coating. This should only be considered for CR-39 and mid-index plastic lenses (in my opinion), and only if you spend a lot of time outdoors. Any chance we have to reduce UV exposure is good. Most glass and high-index material will block out 95-100% of UV light. The law may require a minimum amount of UV protection for anything called "sunglasses," but this coating is optional for eyeglasses worn primarily indoors - don't let anyone tell you otherwise. Don't argue with idiots. If buying sunglasses, get UV coating. If not, skip it.


Anti-scratch coating? I was talked into UV and anti-scratch coatings for plastic lenses many times. Why are you paying to fix up cheap plastic lenses when there is a better material, polycarbonate? It's thinner, harder (otherwise known as bullet-proof glass), less prone to scratching, and naturally filters out a lot of UV light - without coatings. Note - while polycarbonate material is used to make bullet-proof glass, wearing thin, polycarbonate lenses will not stop a bullet nor should they be considered "safety lenses." The trade-off is that polycarbonate material will produce slightly higher unwanted reflections. I have also noted a slight chromatic distortion, but I'm a photographer. The average person may not notice it. My last pair of polycarbonate lenses also produced stress cracks around outside after 5 years which I have never seen on CR39 lenses.

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Scam #3 - Scratch coating. Compare the difference between CR-39 with scratch coating vs. polycarbonate lenses, which are 10x harder - and, don't let 'em sell you anti-scratch coating for polycarbonate lenses - they'll laugh at you when you leave the store. ** Polycarbonate lenses are more reflective and may require optional AR coating.


I have been lured into a false sense of security by talking to a real eye doctor right before the optician. Most doctors I have spoken to are really concerned with your health and the longevity of your vision. They must hand you a written, signed prescription at the end of your examination - it's the law. Many people just take the slip of paper and hand it to the lab, conveniently located down the hall from the doctor. Few people ask for a signed copy for their records. Many people are intimidated when confronted about the request for a written prescription or do not insist to retain their copy.

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Scam #4 - Prescription slide of hand. By law, the eye doctor is required to hand you a written prescription at the end of your eye exam. You typically take this precious slip of paper and give it right back the lab in the same store, ten feet down the hall from the doctor's office. This little piece of paper is your bargaining chip. Do not give up your original copy because you'll never get it back. If they can't make a copy, tell them you'll leave the store to make a copy for them. Retain your original at all times and do not let them intimidate you. Know your prescription. Keep it in your wallet. Speak with your eye doctor and question him when he says he wants to change those numbers. Often, the doctor thinks he is doing you a "favor" by giving you sharper vision when he is really making your eyes more weak.


You should not feel pressured to buy your eyeglasses from the same place which examines your eyes. There are tens of thousands of frames available. Some store manager has decided to stock his shelves with a fraction of what's available. You often wind up buying frames from the first place you stop at. You make a compromise to accept a frame from store stock. Some people prefer to be led by the nose. I prefer a larger selection. Many places will charge you extra for using frames which are not their own. A few places will flat-out refuse to fit frames which you bring in, even if they are the same frames they sold you last year! I've usually paid an extra twenty bucks for the privilege of using last year's frames. Don't put up with it! Tell them, if you charge me extra for using my own frames, I'm going elsewhere (with your written, signed prescription in your hand).

Eyeglasses are difficult to purchase. Instead of breaking down collections by manufacturer and material, most places will scatter hundreds of frames all over their walls. It's maddening to zero in on exactly what you're looking for before being rushed by a sales person. I got tired of the high pressure sales and purchased my frames on-line. There are a few websites which can transpose the outline of eyeglasses over the photo of a person who has the same shape face as you. One website let me upload my own mugshot so I could see the outline of the frames on my own face. Now, this is technology at work! Thankfully, I knew the frame manufacturer, material, and color I wanted - as well as the size (more or less). Purchasing frames on-line took a lot of the mystery out of eyeglasses since it forced me to think for myself.

For example, did you ever question the guy behind the counter holding a ruler up to your eyes? He (or she) is simply measuring your PD (Pupil Distance). Mine is 61mm. Know this number. Measure it carefully - have a friend measure it for you and double-check it. That's your PD. Insist that every time you have eyeglasses fitted that they use the same PD (as an adult). Ever walk out with a new pair of glasses and feel a little dizzy while objects float around you in an unnatural fashion? This is often caused by that guy with a ruler incorrectly guessing your PD. Quit that! Tell them, "My PD is xx millimeters and if you don't use it then I'm going elsewhere. I don't want to be dizzy for a week getting used to new glasses again!"

There are two types of PD, mono/monocular PD and binocular PD. As an adult, unless the bridge of your nose is off-center, you probably want your lenses even spaced. Here is where I trust mail-order labs a bit more, as they feel less inclined to "tweak." Once you have comfortable eyeglasses, engrave your PD measurements in stone and make sure that every lab gives you those numbers. Those numbers will not change! But, after two weeks, your eyes will adjust to the PD set on the lenses. Don't make yourself go through two weeks of being dizzy and nauseous everytime you buy new eyeglasses. Do not blindly accept the numbers which the fitter gives you. Question him if he does not center your eyes in the frame and the nose in the middle of your face. If he gives you a hard time, say "no thank-you" and walk out! Make him earn his salary and your trust. It's your eyes he's mucking with. The PD of your eyeglasses is more important than your prescription, but nobody asks questions about their PD.

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Scam #5 - PD - Pupil Distance. What few people realize is that it takes a minimum of three numbers to obtain eyeglasses. Power of left lens, power of right lens, and your PD. The guy with the ruler quietly records your PD and never tells you what is. Your doctor will often not write it on your prescription As an adult, your PD is yours for life, no matter how bad your eyes get - it never changes. You can order glasses from any lab of your choice, including mail-order labs, if you know your own PD: Knowledge is power.


Mind you, if you have bi-focals, tri-focals, or progressive lenses, the fitter must take additional measurements to find the center of your eyes within the frame. Those of us with single-vision, nearsighted correction can usually toss on a stock spherical lens "off-the-shelf." More on that later.

Another annoying thing about optometrists is that they keep insisting on making my vision perfectly 20/20 (see above for the obscure definition of 20/20). I am not a commercial airline pilot, so the only people who really care how well I see is the DMV (Department of Motor Vehicles). They have an eyechart which insures you can see about 20/40 or better. If it's a little blurry, they don't care. I do not want my eyes "chasing" my prescription. Every time the optometrist makes my prescription a bit stronger, my eyes get a bit weaker. Next year, the cycle continues. And, of course, this leads to buying a new set of eyeglasses. If I have prescription sunglasses or scuba goggles, I have to change all of those as well.

So, I finally had enough. I went into Lenscrafters and asked them for a copy of my old prescription. As I entered, there was only one person who approached me to help. He referred me to the doctor in the back to get a copy. Mind you, I haven't been there in over ten years, so my prescription was not in the computer. I was handed off yet again to someone pretending to look "in the back" (I saw him snicker as he disappeared into the other room), who then returned empty-handed. I was referred to the computer in the front of the store. They told me that I had indeed purchased eyeglasses in the past, but they had simply read the prescription off my old pair - which they added they "don't do anymore."

I asked them for a copy of my current prescription, to which they protested. They would not read it off my glasses, nor would they give me a prescription which I could fill anywhere. They pressed me further, asking me why I needed those numbers, since I could not use them for getting eyeglasses (from them). I made up a story that I was shopping for scuba goggles, which satisfied one lab technician enough to scratch down the numbers on a piece of scrap paper. By this time, there were no less than five people surrounding me, all confronting me about obtaining a new prescription, getting an eye exam, and questioning my motivations for coming in. I took my precious information and ran out the door, less confident in my quest for simply changing my frames.

Later, after I purchased my eyeglasses mail-order, I went back to Lenscrafters and asked for a free adjustment. They did a wonderful job, but I never told them I didn't purchase the eyeglasses from them. There was nobody in the store except for the sales people. When the place first opened, there was a line out the door. There was a line for the cash register, a line for fittings, a line for the doctor, and a line for shopping for frames. It was a zoo. Today, it's a ghost town. Perhaps people got tired of paying for half a dozen hidden charges and getting cheap plastic lenses in return.

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Scam #6 - Old prescriptions. Obtain your written prescription, along with your PD, at the time of your examination and guard this piece of paper very well. If you walk out of the store without it, chances diminish greatly about obtaining it later. Without this paper, you will be required to take another eye exam to buy eyeglasses elsewhere. Without this paper, you cannot haggle with the shop for a better price or threaten to walk out. Some places will refuse to give you a copy of a prescription which is more than six months old. Demand your written prescription. It's the law.


Eyeglass chains will talk to you about the "Life of your prescription." As an adult, my personal experience has been that my eyes are not getting much worse. I have had the same prescription for over fifteen years. The life of an eyeglass prescription is two years. Some will try to sell you stronger and stronger prescriptions to make you keep spending money on new eyewear. They will refuse to give you a copy of your old prescription to force you into another eye exam. Or, they will apply an AR coating to your lenses which will wear out and force you to replace your lenses in less than a year or two. It is good to receive regular eye exams. But, if you feel that your old eyeglasses and your old prescription are fine then keep them. Do not allow anyone to make you spend money. It is you who came to them because you had a vision problem. If you do not have a vision problem, then do not fix what ain't broken.

I phoned around for a shop which would simply replace a scratched lens by reading my prescription off my current eyeglasses. Mind you, I have "single vision" lenses with no astigmatism. This makes all my efforts to duplicate my eyeglasses possible. Tip - while labs are required to get a prescription from a doctor to dispense eyeglasses, there is a loophole which allows some labs to duplicate your existing prescription by reading off the pair on your face. If you need a stronger prescription, then it really is time to bite the bullet and get an eye exam. What's wrong with my old eyeglasses, you ask?

Well, I've been dodging and avoiding doctors for about fifteen years now, ever since someone blew air into my eye and told me it was for a "test." Come on. I'm simply waiting for the technology to improve a bit before I get screened for glaucoma again. I have high quality frames and lenses which have lasted for over ten years. But, for as advanced as the materials are, they could not resist the march of new fashion eyewear. Wow - me, a guy in a short sleeve shirt, jeans, and hiking boots worried about eye fashion? Well...

This all started when I commented to a female friend on how many male suitors were trying to sleep with her. She simply has a look which drives some men wild - very sophisticated, always in fashion, well dressed but understated. I said it was probably her cool-looking sunglasses, which were small, delicate, rose colored glasses balanced on the bridge of her nose. I thought they were kind of cool. This started an "Oh, by the way" conversation, as she pummeled me senseless about the fashion sense of my eyewear. She said that huge, aviator style glasses fell out of fashion years ago. Watching the movie, Hunt For Red October, which was filmed fifteen years ago, I discovered that many of the male actors had indeed worn huge, aviator style eyeglasses in 1990. I was amazed. Nobody was wearing them now. I had purchased these frames around the same time as the movie, probably trying to imitate Hollywood fashion on a subconscious level.

It was indeed time for a change. Why not get smaller, lighter, thinner glasses which weigh a fraction of that of the old clunkers? I mean, if one female commented on my "Geeky-looking eyeglasses," then other female types were thinking the same thing. This theory was proven correct when I later sent a photograph of myself wearing my new glasses to another female friend of mine, who said she wanted to kiss those lips of mine. Hey - sex is good! I love my new glasses!

Out of thousands of frames, I narrowed it down to Flexon #409. My female friend concurred. Mind you, my old frames were also made by Flexon model #11 - about 400 frame styles had come and gone since then. I was really behind the times. Three websites offered these frames for sale. The cheapest place told me I had an "invalid email address" and had a 20% restocking fee. The next two websites were only six bucks apart, but one had an unconditional money back guarantee and very sophisticated software - so, I went with them.

Onto lenses. Glass lenses are heavy, expensive, and very difficult to find. Just about all new lenses fall into three categories: plastic, polycarbonate, and ultra hi-index. Polycarbonate Transitions brand lenses is what I settled on, to the tune of a cool $300. That's a new record in expense for me, but they threw in a cleaning kit and eyeglass case for free. I have been lied to on more than one occasion by someone at Lenscrafters. Back in the 90's, when I inquired about sun-sensitive lenses for the first time, they lied and said that sun-sensitive lenses were only available in glass (Photogrey). They talked me out of them. In fact, Transitions was making a coating for plastic, but Lenscrafters was not selling them. So, they lied to me, rather than sending me to another eyeglass place. A few years later, I wanted Polycarbonate lenses. They told me that their sun-sensitive coating, Flextint, was only for mid-index (plastic) lenses, not hi-index. So, I settled for less. A third time, I asked them just how their Flextint coating compared to the Transitions name brand coating.

They responded to my query about their "Flextint" coating a mere two weeks later. They corrected me that 1) Transitions "lenses" was nothing more than a coating which is applied to other another manufacturer's lenses. This is half true. While Transitions is indeed a lens coating, it is conventionally applied to polycarbonate lenses made by Essilor. Some places offer lenses by Pentax and Zeiss Claret for an extra fee. Lenscrafters offers their own cheap, plastic lenses which are thick and prone to scratching. They continue in the email, 2) We apply the "Transitions" coating to our plastic lenses, along with anti-scratch and UV coatings and call it "Flextint." This is where I find myself hip deep in the bullshit.

There are several competitors of sun sensitive lenses / coatings. Photogrey is a coating for glass lenses - glass lenses aren't around much anymore. Many labs have tossed their glass grinding machines in favor of other materials. Kodak sells SunSensors which have a td of 1.56 - which is a mid-index plastic with a density of only 1.17. It is not a coating, so the entire lens gets dark - not just the surface. It's low density makes it lighter than polycarbonate. It looks like a hot technology, inexpensive, but may require an anti-scratch coating. Rodenstock ColorMatic is akin to Kodak and will turn up to 50% dark while inside of a car. Other technologies do not work while driving in car, since most automobile glass filters the UV light to which they are sensitive. ColorMatic Extra can take an AR coating. But, hands down, the most popular coating is Transitions. In 2002, Transitions III was replaced by Transitions "Next Generation." It is darker and responds much more rapidly than Transitions III but, apparently, costs a small fortune. I take it as a "wash" since they include anti-scratch and UV protection as part of the package. Just about all the major chains carry Transitions brand lenses (coating). So, why is Lenscrafters calling it "Flextint?" Somehow, I have to believe that Flextint is a cheap imitation of the more popular coating. If Joe has a coffee shop and purchases all of his coffee from Starbucks, would Joe sell his coffee under the name "Joe's Coffee" or under the name of "Starbucks Coffee?" Dumb question - there's a reason why he is buying coffee from Starbucks (it ain't the quality) - he is buying the name. Pearle, Sterling, Sears, Cosco, and BJOptical all carry Transitions brand lenses (coating). If Lenscrafters is reselling the same coating, they would sell it as Transitions - the hottest lens coating to come out this century and not "Flextint," a name which they simply made up. Lenscrafters also sells "FeatherWates" instead of a more descriptive name, like "CR-39" or "Polycarbonate." I've been lied to.

I joined Consumer Reports website to compare the big eyeglass chains. Sears rated high in service while low in price. Since I was purchasing my frames mail-order, I wanted to visit a local expert eyeglass fitter. I doubt I paid a "good" price for what I have, which was a total of $460, but I found the quality of Sears Optical to be first rate - not much of a line in frames there, tho. The wholesale clubs offer glasses as well, but I have not braved a route to buying eyeglasses from the same place which sells 50lb bags of frozen chicken wings.

Lenscrafters promises eyeglasses "in about an hour." From my experience, not once did they give me eyeglasses in one hour. And, they have never gotten my glasses right the first time either. Once, they tinted the wrong pair. Another time, they tried to sell me a badly scratched lens after they "buffed it out." The scratch was noticeable the first time I cleaned them; I saw the remains of a huge gash along the inside of one lens. But, the service has always been pleasant (while they ripped me off). They charged me extra for unnecessary coatings, extra for using my old frames, and extra for requiring one lens stronger than -2! (most lenses are available to -8) Do you believe this?

Pearle gave me the worst customer service while charging me the most amount of money. When I bought a pair of Rx sunglasses at Pearle, the optician kept adding on options and coatings until a simple pair of sunglasses priced out at over $500 with plastic lenses. I made her go back and itemize everything, removing anything which was over the top. I think their lens grinding was sloppy as well. When I had them fitted, the optician became impatient with me when I spent more than a few minutes adjusting my glasses - he actually snapped at me when I said I could look over the top and see they were still crooked. Like, hey dude - it's me who has to wear this contraption for the next few years, so let's get it right, ok? Have I returned to Pearle? No. And, after realizing the hype I've been spoon-fed by Lenscrafters, I ain't returning there either.

Three eyeglasses chains have three different names for thin lenses. Lenscrafters calls them "FeatherWates." Pearle calls them "MicroTHINS." Sears calls them "Profile Lenses." So, which is thinner? To compare thin lens technology between the eyeglass chains, you need to know the refraction index. That is, as light passes through air and enters a more dense material, like glass or plastic, at an oblique angle, it will bend. Snellen (who defined the term 20/20 for us) also, apparently, came up with a formula for determining the angle at which light bends to be a constant for a given material. This number is the ratio of the sine of the angle of incidence to the sine of the angle of refraction. Just for kicks, I asked the optician at Sears Optical (aka Cole Vision) what the refraction index of my Transitions polycarbonate lenses were. He gave me a blank stare. Nevermind, I'll do some more research.

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Scam #7 - Friendly technical terms. No eyeglass place I have ever been in used terms like "Refractive Index," "CVF," "R %," "Polycarbonate," or "CR-39." Instead, they use words like "High-index," "FeatherWates," "MicroTHINS," "Profile," and "Flextint." This is how they can sell you cheaper lenses with higher mark-up's and unnecessary coatings. This also makes it impossible to comparison shop. Learn what the materials are and what the nd of the material is. If they cannot tell you the refractive index of a lens, then you are speaking with someone who doesn't know dick about what he or she is selling you. Learn the facts and treat these people like used car salesmen.


Polarizing sunglasses is the proverbial double-edge sward. Be careful when considering polarizing sunglass coatings. If you are buying eyeware for a sport such as skiing or boating, then polarizing sunglasses will greatly reduce glare from snow and water surfaces. It works like this: when light strikes a shiny surface, it becomes polarized. It's like using a knife to cut a brick of cheese into thin slices. The sunglasses have tiny slits in them. If the slits line up with the slices, light passes through. Unpolarized light passes through as well. But polarized light e.g. glare off the water or snow is blocked. There is a danger while driving in a car. Light from a side view or rear view mirror becomes polarized and, depending on the polarization of the eyeglasses, another car's headlights may be completely blocked, making on-coming traffic invisible to you. Some private aircraft have been rumored to have polarized windshields, which can make lights from other airplanes invisible if you are wearing polarizing sunglasses. Just make sure you only use polarized lenses for sunglasses and that wear them in the sun. Never ever drive with polarized sunglasses after dusk. That being said, polarized prescription sunglasses are just wonderful. It takes all the glare and nasty harshness out of the day and turns it into... cool.

If someone tells you plastic, they mean CR-39 resin. It has good optical qualities, but is poor for UV filtering and scratches easily. If someone tells you mid-index, it could mean just about anything - again, plastic and a bit thinner. Hi-index or thin nearly always means polycarbonate. It's a wonderful material for anything less than Coke bottle glasses. Never let anyone sell you UV or anti-scratch coatings on polycarbonate. (any UV or scratch coating for polycarbonate comes from the factory and is already included in the price) It's a bit more reflective, so it may be time to consider an AR coating (not entirely necessary, tho). Ultra-hi-index materials are state of the art, often heavier and more reflective. Do not consider ultra-hi-index lenses unless you have a real need. Ultra-thin or Thin Plus often refers to Aspherical Polycarbonate (see below). Here are the numbers:

nd ne CVF DENSITY UV
CUT-OFF
ABBE R (%)
Glasses
White Crown 1.523 1.525 1.0 2.5 320 59 4.3
Light Flint 1.600 1.604 0.87 2.6 334 42 5.3
1.7 1.700 1.705 0.75 3.2 340 356.7
1.701 1.706 0.75 3.2 320 42 6.7
1.8 1.802 1.807 0.65 3.7 332 35 8.2
1.830 1.838 0.63 3.6 340 32 8.6
1.9 1.885 1.893 0.59 4.0 340 31 9.4
Plastics
CR39 1.498 1.500 1.0 1.3 355 58 4.0
Trivex(r) 1.532 1.535 0.94 1.1 380 46 4.4
Sola Spectralite 1.537 1.540 0.89 1.2 370 38 4.8
AO Alphalite 1.582 1.585 0.90 1.3 380 34 5.1
Polycarbonate 1.586 1.589 0.86 1.2 385 30 5.2
Hoya Eyas 1.600 1.603 0.83 1.3 380 42 5.3
Polyurethanes 1.600 1.603 0.83 1.3 380 36 5.3
1.609 1.612 0.82 1.4 380 32 5.4
1.660 1.664 0.75 1.4 375 32 6.2
Stylis 1.670 1.674 0.74 1.4 375 32 6.3
Hoya Tesalid 1.710 1.715 0.70 1.4 380 32 6.9
Nikon 1.740 1.746 0.67 1.4 380 32 7.3


Eyeglass places will rarely "talk turkey" with you about optics. Being a photographer, this is an area of interest for me. Here's what it's all about.

Spherical lenses are the most common and easiest to manufacture. Spherical refers the to the curve of the lens, which has a uniform curve - like an onion. Smaller onions have tighter curves on them, akin to stronger eyeglass lenses. Aspherical is a curve which is not uniform. They are more expensive to manufacture, but provide a few advantages. Distortion occurs, most notably in reading glasses, outside the center of your focus. Aspherical lenses accounts for this distortion and provides a wider field of vision. They are also thinner than spherical lenses. If you have thick reading glasses, aspherical lenses is something you want to look into, but expect to pay top dollar for them.

nd is the refractive index as measured in the US, ne in the U.K. 1.5 is typical. When someone sells you "Hi Index" lenses, this number should be 1.58 or better. "Very high index" would be 1.66+" In general, the higher the number, the thinner the lens - but, you've got to heed the material used. If you want a wonderful material which is UV and scratch resistant, is lighter and harder than CR-39 plastic, take a look at Polycarbonate. The downside, however, is its ABBE and R%...

ABBE relates to chromatic aberration, you want this number at or above 50. CR-39, for the big, ugly plastic material it is, is very good with chromatic aberration. Polycarbonate is not. I have not had much of a problem with Polycarbonate ABBE, but I have noticed a very slight color blur - only because I am a photographer. It's barely noticeable. If your prescription is higher than -2, you should pay attention to this number.

Will your optician talk to you about the trade-off's of ABBE in hi-index lenses for your prescription? Doubtful! Talk the doctor who examines your eyes about ABBE, not to the guy from whom you buy eyeglasses - he doesn't know and he doesn't care.

R % is the reflectance index, typically 4 for plastic lenses. It's higher in Polycarbonate lenses - so, be careful. If you are bothered by reflections, or if you want to subdue the impact which eyeglasses make on your face, you might consider an AR coating with polycarbonate lenses. I don't like AR, but have annoying reflections at times. I am still happy with my decision about not getting AR. If I ever decide to buy a more reflective material, then I would reluctantly go with AR for R% greater than 5.2

CVF (Curve Variation Factor) is how thin the finished lens will be, compared to CR-39. So, material with a CVF of 0.75 is 25% thinner than plastic lenses. But...

Density is how heavy the lens will be, or the specific gravity. 1.3 is typical for plastic lenses. Note the higher index materials get thinner, but they also get heavier (by volume). If you have my prescription, which is about -2, I would not recommend ultra hi-index material. Although there might be a slight reduction in thickness, the lenses could actually be heavier! I would resist the ultra hi-index material unless you're starting out with Coke bottle glasses.

Today, I paraded my mug in front of my colleagues, expecting everyone to comment on my new eyeglasses. I just spent a month of research and $460 to upgrade my eyewear to something much more fashionable. Nobody noticed. We're all guys. Eyeglasses are background noise. Even the guy who measured my PD for me, whom I told I would be wearing new glasses the next day, did not notice the change. He said, "I thought something was different, but I didn't know what."

Well, hopefully my new eyeglasses will make me more popular with the ladies at the local watering hole.

Henry


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PostPosted: Tue Mar 21, 2017 3:43 pm 
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Joined: Thu Mar 02, 2017 11:35 am
Posts: 46
I haven't updated the information in my opticians rant in a few years but feel the need, having visited a ophthalmologist just this past week. Please allow me to clarify a few things. The ophthalmologist I visited was a great guy - he took the time to explain the differences in my prescription, the trade-off's between tailoring my glasses for driving and seeing in the distance vs. the computer screen, and the up-coming new technologies and break-thru's. Don't be put off by the eye doctor. Just tell him what your issues and expectations are. Be firm but polite and insist he explain everything. They are your eyes.

Polycarbonate lenses... in my previous rant I asserted that they are more scratch resistant than CR39 resin. After doing some more research I found just the opposite to be true. So, how could I have been so wrong in my original research? ah, it turns out that most manufacturers of polycarbonate lenses apply an anti-scratch coating to their lenses - making these lenses once again more scratch resistant than CR39! Don't try to snow me. And, don't try to sell me anti-scratch coatings for polycarbonate. It's already included in the price. Scam artists!

But, I digress. I visited my old friends at Lens Crafters. The ophthalmologist gave me a big sheet of paper with several prescriptions on it - one for driving, one for the computer, and one for sunglasses. He checked off some boxes for polarized lenses and such which was slightly "out of bounds" in my opinion but no harm done. What got me was it was a two-part carbonless form. Wow, take home the canary color for my records. Excellent. Oh, but that means I have to give the lab the white copy which means they won't make glasses from my copy ever again. See Scam#6 and shame on you!


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PostPosted: Tue Mar 21, 2017 3:49 pm 
I just read your comments on opticians. As a practicing optician I would like to congratulate you on most of what you said. A few corrections are in order though. Even though polycarbonate lenses are made for safety conscious wear (E.G. Sports,Kids) they can scratch much easier than most other materials. There surface is softer than plastic and will scratch quicker than most. I do believe safety does come first. Also as depicted in your chart, the best clarity is crown glass, which is depicted by your ABBE value of 59. This is the reason most people see or do not see as clear through the material. All opticians do not know the index of refraction or quite frankly the relationship of a prescription to the materials used. If you want a professional you need to use a professional. Most states require a licensing requirement, unfortunately mine does not.

Scratch coating is not as important if you take care of your glasses properly. UV is very important on plastic lenses. With the proper protection you filter almost 100% of UVA and UVB light. I am not saying that the wrath of GOD will come down and blind you, but having that little extra precaution is worth the few bucks. And as you said it is a must for any sunglasses.

Polarized lenses filter the light coming off the ground as you said, but they work exactly like non-polarized for light that does not reflect off of a surface. Common complaints are that a person sees the tempering in some car windows (looks like purple squares) and digital displays on gas pumps can not be seen. All in all they are worth every penny as a sunglass.

Unfortunately, there are some places that sell 1-2 layer AR coatings, what I like to call a "crappy paint job". The reason a good AR coating works is that it flexes with the lens. By the way the scratch coatings are actually in one of those layers which are measured in microns. The AR coating will let 99% light into your eyes, to compare this vision look out of a window at the vision, than open the window and you tell me which seems better. When light is transmitted through any material it is bent, when more light travels through it gives you a clearer picture.

I am truly sorry that you received the horrible treatment at some of these places. I would just like to let you know that there are plenty of places that the optician values your vision over the price.

I too will put lenses in your own frame, whether one or two. This is done with the knowledge that the lenses might not match in color do to weathering (the lens treatments fade with time, the 1st year you may have 100% UV protection by the time the second year comes around the UV block may be 70% depending on how much time the lenses were exposed to direct sunlight. Also that if the frame breaks we can not be responsible).

The prescription is yours, you do need to take it. If you give the prescription to the shop you are getting the glasses at, ask for it back when it is done or as you said have them make a copy. Asking for a copy of your prescription from ten years back is a little ridiculous. If that was me I would take your phone number and a non-refundable deposit for the time and effort of paying someone who would need to look through the archived records (if a physician maybe, if just a store they might not even keep inactive records that far back).

Douglas B Wohl
Wohl Optics http://www.wohloptics.com/


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