Archive for the ‘Glasses Facts’ Category
If you like the way the anti-reflective (AR) coating on your eyeglasses reduces glare, you can thank Mothra – or a real-life moth – for that.
That’s because moths’ eyes are covered with a special film that eliminates reflections. This is necessary because of their well-known attraction to flames.
No, not that kind of flame! This kind:
If moths’ eyes reflected light, it would alert predators to their presence. But moths’ eyes are coated with a super-thin film structured in a hexagonal pattern of bumps that are so tiny they are smaller than the wavelength of visible light. These bumps reduce reflections from flames or other light sources by matching the wavelength of visible light, which blocks the light’s reflections.
AR coatings on eyeglasses take their cue from the eyes of moths. They work in a similar way, using a super-thin layer of metal oxide to reduce reflection by matching a reflected wave of light with an equal and opposite “incident wave” (roughly oversimplified, an interfering wave), which causes the two waves to cancel each other out.
You don’t have to be a scientist, or even an accomplished graph reader, to see that the red wave of the reflection is equally matched by the black incident wave of the AR coating, which blocks the reflection on the lens as effectively as Jerry Kramer blocked Jethro Pugh in the Ice Bowl. (What? Ask a football fan or Google it.)
AR coatings are highly recommended for eyeglasses. They’re especially useful with high-index prescription lenses, because high-index lenses are thinner, lighter, and flatter than standard- and mid-index lenses, and therefore tend to reflect more light than lower index lenses do.
But all lenses, even non-prescription lenses, benefit from AR coating, especially sunglasses.
However, one of the most important uses of AR coating will not involve sunglasses, unless you’re this guy.
For most people, who, unlike Corey Hart, don’t wear their sunglasses at night, AR coating is a must-have for driving glasses, prescription or non-prescription sunglasses, or clear prescription lenses. AR coating is great for reducing glare from streetlights, stoplights, taillights, and oncoming headlights. It’s especially good at decreasing the “halo” effect.
Wait, not that halo effect – that one should only be increased! Multiplied, even, at every possible opportunity. Here is the halo effect you want to reduce:
AR coating has daytime and indoor uses, too. It’s great for people who spend a lot of time on the computer, since it reduces glare from the monitor, which can cause eyestrain.
AR coating performs a great cosmetic function, too. It greatly decreases the reflection on eyeglasses’ lenses from external indoor and outdoor light sources. With AR coating, people looking at you while you’re wearing glasses will see your eyes rather than what’s reflected on the lenses. This is an excellent feature to have, unless you’re acting in Alfred Hitchcock’s Strangers on a Train.
If you haven’t seen that movie, check it out. It’s one of Hitchcock’s best.
In a minute we’re going to examine the three main types of AR coatings available for eyeglasses’ lenses: standard, hydrophobic, and oleophobic. They all work the same way, by blocking reflection and reducing glare with one or more layers of metal oxide that (remember the moth) allow more light to pass through the lens.
But first, let’s dispose of the most common misconception about AR coatings: that they tint the lens. This is not true. AR coatings are clear and colorless and invisible on the lens.
But there is a color-based way to tell if your lenses have AR coating. Sometimes people will think that, because reflections on the lenses are not entirely eliminated, their glasses don’t have AR coating, even though they ordered it.
To see if your eyeglasses have AR coating, hold the glasses parallel to the ground, with the temple arms (the stems that go behind your ear) up or down. Angle the glasses so you can see reflections on the lenses. If the reflections look green or purple, your lenses have AR coating.
Here’s why: The reflections will look green or purple, or both green and purple, because AR coating blocks waves that are in the green-to-purple wavelength of the spectrum of visible light. That’s why these colors are reflected on the lenses. If that’s not confusing enough, here’s a chart that will really have you scratching your head, unless you’re an optics geek:
Now that your brain has recovered (we hope), let’s look at those three main types of AR coatings: standard, hydrophobic, and oleophobic. Standard AR coating, which is $4.95 at Zenni Optical, and which can cost north of $100 at other optical retailers, does a great job of reducing reflections on eyeglasses lenses.
But there’s a big difference between standard AR coating and hydrophobic, which is $8.95 at Zenni, and oleophobic, which is $14.95 at Zenni. These AR coatings can cost as much as $200 at other optical retailers.
The hydrophobic AR coating is called that because although it blocks reflections the same way the standard AR coating does, it’s also water (hydro) resistant (phobic). It puts a slick surface on the lens that resists the buildup of water-based moisture, which is important to have when you’re watching a tearjerker like The Best Man Holiday for the 87th time.
The hydrophobic and oleophobic AR coatings make your eyeglasses’ lenses easier to clean than lenses with the standard AR coating. You can do this experiment yourself. If you have a pair of glasses with standard AR coating and a pair with hydrophobic or oleophobic AR coating, clean each pair with the cloth that comes with your Zenni glasses. It’s much easier to clean the hydrophobic or oleophobic pair than the standard pair, right? The cloth slides right across the surface of the hydrophobic- or oleophobic-coated lenses, while on the pair with the standard AR coating there’s a little drag on the lens.
Stop it! Behave. It’s not that kind of flame and not that kind of drag.
The oleophobic AR coating is called that because in addition to resisting water the way the hydrophobic AR coating does, it also resists oil and grease (that’s the “oleo” part, as in “oleomargarine,” which is what margarine used to be called).
The oleophobic AR coating has a slick surface on the lens that, like the hydrophobic AR coating, resists the buildup of water moisture on the lens and makes the lenses easier to clean than lenses with the standard AR coating.
But it also protects against smudging from fingerprints as well as facial oils. This is useful when you don’t want to use your superpowers to clean your glasses, which would give away your secret identity.
Zenni also offers special mirror-finish oleophobic AR coatings for sunglasses. These come in gold, silver, and blue, and each is $19.95. The back of the lens has the AR coating, and the front of the lens has the reflective mirror-finish coating. The gold mirror finish looks great with frames that are gold, red, brown, or tortoiseshell, such as frame A10102114.
The silver mirror finish looks great with any frame color or style, especially A10102412.
The blue mirror finish looks great with silver, black, gray, blue, or gold frames, such as 521814, and is especially good at reflecting harmful blue light.
Or check out this beauty in the blue mirror finish. The frame (A10161222) looks great, too.
Speaking of reflecting harmful blue light, soon we’ll be launching our newest AR coating, which is specially designed to block blue light. Keep checking the Zenni Blog – and website – for details!
Friday, March, 14 2014 by Matt Souza
But if you have a strong prescription and you’re ordering your glasses online, figuring out how to get the thinnest lenses possible can be perplexing.
Not to worry!
We’re going to make it easy for you.
All you’ll need is your prescription and a handy online tool that will estimate how thin your lenses will be.
This handy online tool is the Lens Thickness Calculator. It can be found here, at the OptiCampus website.
Before we talk about how to use the Lens Thickness Calculator, let’s look at the factors that can thin your lenses:
1) Your prescription. This you cannot change to get a thinner lens. Doing so would be counterproductive, in that you would not be able to see well if you take it upon yourself to lower your prescription below what your eye doctor has prescribed.
As a general rule, single vision prescriptions result in thinner lenses than multifocal prescriptions, all things being roughly equal. Multifocal prescriptions are those with an NV-ADD (Near Vision reading ADDition). Having an NV-ADD, or just an ADD, as it’s usually written, enables you to get bifocals and progressive glasses.
In addition, prescriptions with astigmatism corrections – if you have this, there will be numbers in the Cylinder (CYL) and Axis (sometimes abbreviated X) fields – generally result in thicker lenses than those without astigmatism corrections.
2) Your lens index. The lens “index” is short for the lens’s “index of refraction.” That means how much the lens bends the light that enters it. That’s what refraction is. Bending the light focuses it right into the middle of your visual sweet spot, the retina, so you can see well.
You can change the index to thin the lens, up to a point. After that point, the law of diminishing returns kicks in. The lens that is recommended for your prescription will be the thinnest lens. Choosing a lens index that’s higher than the recommended lens index won’t make the lens thinner, and you’ll end up paying more for no improved result.
If this is confusing, don’t worry. We’ll clearly explain where the point of diminishing returns shows up when we look at the various lens indexes. In addition, you’ll be able to see it too, when you start playing with the Lens Index Calculator.
3) Your lens width. This can have a considerable effect on your lens thinness. Once you have settled on the correct lens index, having determined that going to a higher lens index number won’t result in a thinner lens, the lens width – also known, weirdly, as the “eye size” – will be the last, and in some situations, the most important – factor in thinning your lens.
OK, are you confused enough yet?
Yes? Let’s fix that right now.
We’re going to look at a prescription to see how different index numbers can make the lenses thinner. We’ll change the lens width – remember, that’s also known as the “eye size” (even though it doesn’t refer to the size of your eye) – to see how this affects the thinness of the lens.
To do this, we’re going to use a fairly common prescription. Most eyeglasses wearers are nearsighted, which means that the number in the Sphere (SPH) section on the prescription will be minus.
Most people who have an SPH correction also have an astigmatism correction. So we’re going to create a common prescription, with an average Pupillary Distance (meaning the distance between your pupils measured in millimeters, PD for short), 63; an average lens width (all together now: also known as “eye size”), 50 mm; and an average bridge (that’s the part of the frame that goes over your nose), 18 mm.
Here it is:
SPH -2.00, CYL -1.00, AXIS 90, PD 63, Lens Width 50, Bridge 18.
(For the sake of simplicity, we’ll assume that the prescription is the same for both eyes.)
Let’s put these numbers into the Lens Thickness Calculator and see what we come up with when we use different lens indexes.
With nearsighted prescriptions, the lens is concave. With farsighted prescriptions, the lens is convex. A concave lens is thinner at the center, thicker at the outer edge. A convex lens is the opposite.
You will see then, that with nearsighted prescriptions, the Center Thickness of the lens will be a lower number than the Edge Thickness.
Here’s what our formula yields with the 1.50 standard-index lens, which comes free on an order of single-vision glasses:
Center Thickness (CT): 2.0 mm / Edge Thickness (ET): 4.4 mm
Nice and thin at the center, but maybe not as thin as it could be at the outer edge. Let’s try it with the 1.57 mid-index lens and see what we get:
CT: 1.5 mm / ET: 3.6 mm
That makes the lens thinner at both the center and edge, and the lens is still free. Now let’s try it with the 1.59 pure polycarbonate single-vision lens, which costs $9.00, and see what happens:
CT: 1.5 mm / ET: 3.5 mm
You’re spending $9.00 for this lens, which is not a huge amount, but this slightly higher index doesn’t make the eyeglasses lens perceptibly thinner than the free 1.57 lens does. Now we’re starting to see the law of diminishing returns come into play.
However, even if the lens would be just as thin with the 1.57 lens, it would be worth it to spend the $9.00 on the 1.59 pure polycarbonate lens if you’re getting rimless glasses or if you’re buying glasses for kids who can be expected to treat the glasses roughly.
That’s because the 1.59 lens is a more impact-resistant lens than the 1.57, which is still a fine lens for people who treat their glasses with care.
Now we’re really going to see the law of diminishing returns at work when we go up a notch, to the 1.61 high-index single-vision lens. Here are the results of this lens:
CT: 1.5 mm / ET: 3.5 mm
No change, and you’re now (theoretically) spending $19.95 on a lens that isn’t any thinner than the 1.59 pure polycarbonate lens that’s $9.00, and is only a tiny bit thinner than the 1.57 mid-index lens that’s free.
But even after you’ve selected the lens index that will give you the thinnest lens, you can still thin the lens further, if you narrow its width.
Let’s lower the lens width to 48 mm and see what happens with each lens. First, the 1.50 lens:
CT: 2.0 mm / ET: 4.1 mm
The Edge Thickness is a tiny bit better, 4.1 mm as opposed to 4.4 mm on the 50 mm-wide lens. How about the 1.57 lens?
CT: 1.5 mm / ET: 3.3 mm
Now we’re talking! We’ve shaved half a millimeter from the center and almost a whole millimeter on the edge, just by lowering the lens width.
How about with the 1.59 lens?
CT: 1.5 mm / ET: 3.2 mm
No change on the center, only one tenth of a millimeter on the edge. Stand and salute the diminishing returns on parade!
Let’s take a quick look at the 1.61 lens, just to make sure it doesn’t make the theoretical eyeglass lenses any thinner:
CT: 1.5 mm / ET: 3.2 mm
That would cost $10.95 more for no improved result.
So unless you want a pure polycarbonate lens for its impact-resistance feature, you’re wasting your money by spending $9.00 to get a higher-index 1.59 lens that won’t be any thinner than the free, 1.57 mid-index lens.
But once you’ve confirmed which lens index that will result in the thinnest lens for your prescription, and you want to thin the lens even further, play around with the lens width on the Lens Thickness Calculator. Go as low as you can and still keep the lenses wide enough for a comfortable field of vision and attractive look.
For example, the 48 mm wide lens may be just as narrow as you can go without making the glasses look too small. But if you can narrow the lens even more, you will see that the lens will continue to become thinner.
If you do check out the Lens Thickness Calculator to see the estimates of different thicknesses that different lens indexes and lens widths yield, keep a few things in mind: When you are selecting the Lens Material Type, the categories listed on the Lens Thickness Calculator don’t exactly correspond to the lens index categories on our website, although they are basically the same.
For example, the Hard Resin lens is the 1.50 lens. The 1.56 mid-index is essentially the same as the 1.57 mid-index. The polycarbonate lens is the 1.59 mid-index lens. All of the 1.60 lenses on the Lens Material Type list are the equivalent of the 1.61 high-index lens.
So to recap, stick with the lens that our website recommends when you enter your prescription. That will get you the thinnest lens for your prescription, if you also select the lowest lens width that will also work well for your face size and shape.
Thursday, February, 13 2014 by Matthew Surrence
Writing for an eyeglass company blog has some strange benefits, including staying up to date on eyeglass-related crime. While I’ve always thought of sunglasses as a semi-effective disguise for criminals, the news proves that eyeglass involvement in criminality is far more varied than I thought: More than a few people are wanted for stealing eyeglasses, while other criminal suspects have been accused of using them as courtroom props. Even more bizarre is the occasional use of eyeglasses as weapons, as well as Robocop-like law enforcement technology.
Here are a few examples:
I had no idea that eyeglasses were such a hot commodity, but a simple search for “eyeglass theft” on Google news revealed a surprising number of cases. One story reports that a woman allegedly stole $2,300 in designer glasses, while another reports that a couple armed with a baby carriage allegedly robbed an optometry clinic, taking off with glasses, frames and even equipment.
Eyeglasses as a Defense Team Prop
The ongoing Jodi Arias murder trial has attracted a lot of media attention, particularly since the accused underwent a “makeunder” between when the crime occurred and her trial. In addition to changing her hairstyle and the way she dressed, Ms. Arias began wearing glasses. Some commentators believe that she’s using the glasses as a to make herself appear more intelligent and trustworthy.
Will this strategy work? The verdict is still out.
Eyeglasses as a Murder Weapon
In February, a convict being transferred cross-country to serve his sentence used his (broken) eyeglass frames to stab the detective guarding him. He escaped custody and sparked a statewide manhunt. (The fugitive was eventually captured and returned to custody.)
Using Glasses to Spot Crime
It’s not only criminals who are fond of their glasses: Police officers in Brazil are using glasses with facial recognition technology to scan faces and identify potential criminals in a crowd. While some people are concerned that these glasses might infringe on civil liberties in cases of mistaken identity, others think that they can help prevent serious crimes from occurring at large events.
Sunday, November, 24 2013 by Lainie Petersen
It’s almost back to school time again, so why not ease into things with a little fun American History 101 on everyone’s style fave — aviator glasses? The credit for their invention goes to John A Macready, a US Air Service pilot and Army aviation instructor. Back in the early 20th century, test pilots were freezing their – yes eyeballs — off and Macready’s friend, Shorty Schroeder, was no exception.
The blinding sunlight and extreme temperatures that came along with taking biplanes past 33,000 feet was taking their toll on Shorty’s and the other pilots’ eyes despite wearing goggles, so Macready decided to team up with Bausch and Lomb, who were producing eyeglasses in Rochester, New York at the time. In 1937, Bausch and Lomb took out a patent for the first aviator glasses although the eyewear was named “Anti-Glare”and not the much more adventurous sounding “Aviator” back then.
The invention had a gold-plated wire frame with goggle-shaped lenses made of green mineral glass. Thanks to Macready, the Anti-Glare had an elegant design (Thanks, Macready!), but the best part for the sake of pilot eye health was that the lenses filtered out both ultraviolet and infared light rays. Because of this banning of the rays so to speak, Ray Ban became the division of Bausch and Lomb devoted to the new Anti-Glare eye safety device that quickly became sought after by the Air Corp aviators. Soon, these glasses used by aviators became known as aviator glasses, which makes sense.
After General Douglas MacArthur and his air team in the South Pacific in the 1940s wore the aviator glasses, the demand for them back in the United States began growing steadily. All these decades later, elegant aviators are still in high demand! (Thank goodness the same can’t be said for those hideous-looking corn cob pipes he used to smoke!)
To keep up with the demand for aviator glasses for both practical sun-protection and fashionable eyewear, many different companies began manufacturing the glasses in many different styles and colors.
Get these great purple Zenni’s Aviators for just $25.95!
In 1986, Tom Cruise starring as an aviator wearing aviators in Top Gun sparked a major fashion resurgence of the eyewear. Celebrities as diverse as Michael Jackson, Jennifer Aniston and Hillary Duff wore their own favorite versions of aviators to create stand-out looks.
Aviators never ever seem go out of style and this summer, tinted versions became hotter than summer days!
We’re soooo glad that aviators are here to stay. Aren’t you?
Thursday, September, 12 2013 by Ryan
The realization of a need for reading glasses usually kicks in when the smaller print we’ve been seeing no problem, such as the small font used at the bottom of a grocery coupon or on a bottle of over-the-counter headache medication, suddenly seems to be impossible to read.
As we age, our eyes just can’t focus as well as they used to on close up objects. The tech term is presbyopia which comes from the Greek words “ops” for eyes and “presbys” for elder. Here are some interesting facts on presbyopia and aging, followed by some suggestions for Zenni reading glasses that are both stylish and sensible:
* Scientists are as yet unable to fully explain the exact reasons why presbyopia is likely to occur during the natural aging process. Research suggests that it may be a result of reduced elasticity in the lenses of the eyes — and we know this certainly happens to aging skin.
*Although presbyopia, and the need for reading glasses, happens most commonly between ages 40 – 50, the fact is that even by age 25, many of us are experiencing a decline in our vision of objects up close. This may just involve not being able to see the objects or small print in a dim light when before, as a child or young adult, we could see these things in any kind of lighting.
*Symptoms of eye strain, such as headaches and/or sore eyes, while doing close up activities such as reading, needlework, repair work or puzzles, may be a sign of worsening presbyopia that requires reading glasses. Since eye strain is caused by the eyes having to work harder to focus and reading glasses provide better vision to aid the eyes in focusing, many people find headaches and soreness in the eyes to be either greatly reduced or no longer present by wearing these glasses.
*Studies show that people whose work involves close up tasks, such as factory inspectors and jewelry makers just to name two, tend to go to their eye doctor about reduced near vision sooner that those who are not employed in these sorts of fields. The best thing to do is not to wait at all though, since why suffer from eyestrain if a pair of reading glasses is going to solve the problem? This is most likely why most people do eventually face their presbyopia and why reading glasses remain so popular in our aging population!
What To Look For When Selecting Reading Glasses
Choose lightweight metal or plastic reading glasses. If you have metal allergies, go with hypoallergenic metal frames.
Adjustable Nose Pads
Look for reading glasses with adjustable silicone nose pads since they are best for helping to prevent eyewear from slipping. Many people read with their heads lowered or in a reclining position, so having glasses that don’t slip is essential.
Be sure to consider your face size and the frame size. Zenni’s frames are identified in the online catalog on a scale of small to large fitting. If you have a large face and pick a frame that is too small, or have a small face and opt for a large frame for your reading glasses, this may weaken the effect of the vision correction properities and cause eyestrain. Take the time to select the correct frame size for your face. (To check out Zenni’s large selection of glasses that you may want to order as reading glasses, just click on any of our suggestion models below to access the online catalog.)
Look for Zenni’s great features such spring hinge closures, metal for strength and flexible plastic for “give.” These really add up to durable reading glasses — especially if you tend to fall asleep while reading. You don’t want to wake up to find a pair of mangled glasses!
Pick a pair of reading glasses that thrill you to wear and you’ll most likely remember to always put them on when scouring the newspaper or turning the pages of the latest bestseller. If you need a pair of reading glasses for work, consider getting two pairs — one for home and one for the office.
Great Zenni Custom Reading Glasses Ideas:
(Click on the images below for more info)
Wednesday, August, 28 2013 by Ryan