For instance, in the United States, glasses have to be made to strict standards, as regulated by the American National Standards Institute (ANSI). These standards ensure that the glasses are made properly so that the wearer is experiencing the prescription as close to prescribed as possible. When glasses do not meet these standards, the wearers may experience double vision, blurry vision, headaches or dizziness and nausea. I don't know about you, but I wouldn't want someone with those symptoms driving on the same road as me. Countries vary in their standards, and the lines get even blurrier when the glasses are being sold out of their manufacturer's country. So, when an American orders glasses online, they may be getting glasses made in a different country with less stringent standards, or where there is a loophole in those standards because they are being made in one country but worn in another. That's not to say that busy optical shops in the U.S. are getting it right every single time. It is not uncommon for some of our patients to shop elsewhere for their glasses, either due to insurance coverage or seeking a less expensive alternative, and come to my clinic to have us look at the glasses that were made to see if they were made correctly. There are certain "two-for" shops in my area that consistently dispense glasses that don't meet standards, and I write down what is "off" so they can be remade. They have to, it is the law. At least when it is local, I can help, even though they didn't purchase them from me.
In order to purchase glasses online, you need to enter at least one measurement, called the Pupillary Distance (PD). This is a measurement taken by the optician when you sit down to order glassees. Contrary popular belief, is not the measurement between your pupils. It is actually a measurement that takes the reflex of light off the back of the eye, which tells the lab where to grind the lens so that the clearest point in the lens lines up with the place where that light hits your eye. Some people have quite a different reading in one eye than the other, it is biological, but can also be the result of medical changes, anything that affects the brain or nervous system can cause the numbers to fluctuate. Some websites will allow you to enter one reading for each eye, while others simply want to know the total number for both eyes and they will divide that number in half. For instance, if the right eye is 30mm and the left is 34 mm, a total reading of 64 mm would mean the reading for each eye would be 32. As you can see from the example, neither eye is going to be set in the correct place. Though this is more separation than most people experience in their readings, it can be very problematic if the website splits one large number instead of taking two separate readings. While your eyes work together to provide clear vision, having those numbers wrong can feel like looking through binoculars that are too wide or two narrow for you, like constantly searching for the clear part of the lens but feeling like you are not finding it with both eyes at the same time.
In the office we typically take another measurement called the Optical Center height. Where the PD is a horizontal placement, the OC height is a vertical measure of where your eye sits in the frame. Anytime your eye is looking through the center of where your lens is ground, you are getting your best vision, and anytime it is looking away from that area, you are getting less-than your bets vision. Depending on the strength of the prescription and the size of the lens, there can be a lot of distortion that takes place when your eye does not sit in the area where the lens was centered or ground. This measurement is not required online, and some optical shops don't bother to take this measurement. I enjoy impressing my customers with really clear vision by taking this extra measurement. When ordering bifocals, and additional or separate measurement is needed to tell the lab where to set the prescription or reading area in the lens so the eye can naturally flow through the areas of lens to get exactly what it needs in the expected and natural place. I would never recommend ordering bifocals online. This measurement is too crucial, and there is no reliable method of getting an accurate measurement without sitting with an optician in person. This measurement, called a Segment Height (often shortened to "seg height") is in reference to where your eye sits inside a particular frame. Each frame you put on will potentially have a different measurement as we measure how much distance there is between a set spot (which varies depending on the type of bifocal chosen) and the bottom of the particular frame chosen. In the office, a good optician will adjust the frame to fit as you intend to wear it before measuring, to ensure proper placement and grinding of the lens. It matters to me tht my customers can see well, and I pride myself on being thorough because it is senseless to have an eye exam and pay money for glasses if the end result leads to not being able to see well. With a few extra steps and some expert advice from someone whose reputation is at stake, the majority of my customers walk out very pleased with their new glasses. While I know that not everyone can afford to shop in the pricier places, and not every pricey place has expert opticians on staff, there are certain trade-offs that need to be understood in purchasing glasses in less expensive shops. I often equate it with furniture or cars. If you buy a bookshelf from the place where you get your groceries, it is probably not a piece of furniture that you will have around long enough to pass down as an heirloom for generations to come. But, you will be able to afford to replace it more frequently. Just like cars, there is a reason a luxury car costs more than a budget vehicle. Performance and craftsmanship are features you pay for, as is the attention to details that make life easier. If you are buying inexpensive glasses, you should expect to have to replace them more frequently. A quality pair of frames made with good materials should last at least two year ( and in many cases, much more if they are properly cared for). Inexpensive glasses may only last half as long. Common failures are in anti-reflective coatings applied to the lenses, scratches and failure of the spring hinges of the frame.
I am torn about giving out the PD measurement for people to buy their glasses online. It doesn't require a lot of time and effort for me to take the measurement, but in asking for it, my customer is basically asking me to give them something that will enable them to purchase their glasses elsewhere. On a surface level this bothers me because I am in sales, I make commissions on what sales I have and it seems really tacky to ask for help buying something somewhere else. I mean, I wouldn't go to a car shop and ask the dealer for inside information on how I could score a better deal at his competitor's lot. On the other hand, I want my customers to have the correct information so they can have glasses that work for them, even if they don't buy them from me. Many times they come back irritated that their "cheapies" didn't work and price up glasses with me. It comes down to expectations. If someone has ordered top-of-the-line no-line bifocals from me in the past and is now expecting to get their $70 pair online with the same result, I would try to educate and caution them. There is a lot that can go wrong with no-line bifocals, they are complex lenses. In the end, people will make the decision that works for them and I won't interfere. I believe the proof is in the pudding as they say.
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