The Anti-Reflection coatings course, which follows, begins with a brief history, then goes on to discuss the Patient benefits of AR. It continues with a description of some technical aspects such as Constructive and Destructive Interference, and then provides an overview of the current technologies and equipment used in the actual AR coating process.

The second part of the course describes in-office techniques that should be used to help prepare lenses for the AR coating process and includes tips for cutting and edging lenses as well as the use of AR with certain cosmetic lens treatments such as tinting and edge polishing. The course concludes with techniques that can be used for effectively presenting AR coating to Patients.

Much of the information contained in this course is provided courtesy of the AR Council. The AR Council is a non-profit industry association, that was founded in 1989 and is comprised of a variety of companies with a strong interest in anti-reflective coatings. It promotes the use of anti-reflective coatings on eyewear through education, marketing, public relations and advertising.

Anti-Reflection Lens Coating Overview


AR improves a Patient's appearance by making their lenses appear to
be virtually invisible by reducing the glare on the surface of the lenses.
And the Patient's vision is improved due to the transmission of more light.

The most obvious and demonstrable advantage in the use of an AR coating is its visual and cosmetic improvement qualities. AR coating reduces reflections off the front and back surfaces of the lens that allow many people to actually see better, especially at night.

From left to right are lenses without coating, single coated, and multicoated.
From the first to the third image the light
transmission improved from 96% to 99.5%.

Anti-reflective coatings have been popular for many years in Europe and Asia because of the visual and cosmetic improvements to the wearer. It is estimated that only about 12-15% of optical prescriptions in the United States are coated with AR, compared with 65% in Europe and 95% in Japan. Part of the reason for the relatively low acceptance in the United States is the popularity of plastic lenses; it is more difficult to reduce reflections on plastic lenses than it is on glass. While anti-reflective coatings have obtained a reputation as being difficult to clean and easy to scratch, recent improvements in coating and lens technology have begun to overcome these earlier objections resulting in a more viable product.

It was in 1892 when the principle of “thin film coating” was first discovered. Dennis Taylor, an English scientist, found that an older lens that had been oxidized would transmit more light than a newer lens. The cause of this phenomena was tarnish which had, with time, accumulated on the lens through oxidation. Taylor accidentally discovered that the tarnish caused improved light transmittance through the lens. By 1904, Taylor patented a method for artificially aging lenses by using a method of chemical treatment.

Forty-three years later modern AR coatings were developed in Germany, but were held by the government for military reasons until 1939. The first introduction for ophthalmic purposes didn’t come until 1957 for the glass market and 1974 for plastic ophthalmic lenses. This early introduction was in Europe only.

An AR coating is a very thin film. Because it is less than one wave length of light in thickness it is measured in angstroms, which is one-tenth of a billionth of a meter. A simple analogy may work better in understanding a “thin film” coating. Imagine a plaster wall 150 feet thick with a covering of wallpaper. That proportion of wallpaper would equal the thin film of AR coating on the front of a lens 2 mm thick.

Examples of the latest in thin film AR coating

At left a single coated lens using thin film in the 1950's - 1970's.
At right a more recent lens. Green-purple
reflections means all lenses are multicoated.

AR coated lenses can also significantly improve night driving vision. The contrast of bright lights from oncoming cars against the blackness of night increases the incidence of noticeable reflections for the wearer which can effect visual acuity.

One of the most frequent complaints of eyeglass wearers is the
"halo" or "starburst" effect from lights at night. AR significantly reduces
these effects, producing a remarkable improvement in night vision.

This is especially true while driving at night. Reduced glare from surrounding
lights as well as oncoming headlights enables you to drive more safely at night.

Anti-reflective coatings are part of a larger family of “thin film” coatings which can be deposited on a lens or other transparent media by a process of vacuum deposition. You would not want to buy a multiple lens system, like those found in microscopes, telescopes, binoculars or cameras, without an excellent anti-reflective coating applied. Each lens in the instrument would reduce the light transmitted to the eye in succession. Thus, the object being viewed would appear more dimly lit or less bright than it would with AR coating. Multiple lens systems with AR coatings have been used for years by manufacturers of quality cameras. Without a good AR coating, “ghost” images caused by internal reflections, can appear and ruin your photographs.

General uses of AR coated lenses

Ophthalmic Optics
Laser Mirrors
Microscopes
Binoculars
Aircraft Instruments
Precision Optics
Cameras

Ophthalmic optics

Although the reflections most obvious to the observer are seen from the front surface of the lens, half of the reflections seen by the observer standing in front of the person wearing the glasses are, in fact, caused by the rear surface of the lens. Bright objects to the rear of the wearer will also cause a reflection from the front and rear surface of the lens to the wearer’s eye.

One of the most common reflections is that of the wearer’s own eye. These reflections are generated from both the front and rear surface of the lens and will include the wearer’s eyelashes and facial skin in the immediate area of the lens. These so-called “ghost” images are reflected toward the optical center of a minus lens. Reflections will not exceed more than 8% of the total light or 4% per surface as a general rule, but represent a significant number of distractions to which a wearer will be subjected. These reflections, plus the reduced light transmitted to the eye, can impact the vision of the wearer.

Only 92% of light entering an uncoated CR-39 lens is transmitted through the lens; with a multi-layer coating that number increases to nearly 99.5%. Both sides of a lens should be coated to maximize efficiency. A multi-layered anti-reflection coating for the lenses will improve the aesthetics of a high refractive index material (1.6 or greater) more than CR 39 because high refractive index materials naturally reflect more light. A material with a refractive index of 1.6 transmits only about 87% of incident light with 13% lost to reflections. An anti-reflection coating will increase the percentage of transmitted light from 87% to 99%. AR coating is also especially effective with aspheric lenses since the flatter back surfaces tend to create more back side reflections.

At left an untreated lens displays glare.
At right an AR coated lens. Light transmission is improved by 4%.

When light enters the lens, a portion of that light is reflected from the front surface; about 4%. This means that light transmittance is reduced by 4%. This happens again on the rear surface of the lens, but for this discussion only the front surface will be considered.

To better understand how AR coating works, lets review the basics of wave theory. We’ll start with an analogy. Imagine two stones thrown into a pond or rain drops hitting a puddle. The waves emerging from two stones or drops of water eventually run into each other canceling each other out. This is actually the theory of “wave interference” at work. There is positive or “constructive interference” and negative or “destructive” interference.

Let’s look at constructive interference with this simple example. One pile of sand added to another equals a pile twice as high. Add a pile of sand to a hole in the ground of the same volume and zero is the result. This is a visual example of destructive interference.

Constructive Interference
Add two piles of sand together and the result is a pile of sand twice as high.

Destructive Interference
Add a pile of sand to a hole in the ground of the same volume and the result is zero.

Anti-Reflection Coating
Technical aspects

Returning to the light wave, the same principle applies. Add the “plus” waves together and the height of the new wave doubles. That is constructive interference. But reverse one of the waves or make a negative image of it, and then add the plus wave and the minus wave. The result is zero. That is destructive interference.

Now consider the lens and how this application works to help. Light waves enter an uncoated lens at obtuse angles causing reflections on both sides of the lenses. After the AR coating has been applied only direct light is allowed to pass through the lens. This occurs because the thickness of the coating is measured precisely in wave length thickness. To be more precise, it is one quarter of a wavelength. This means that the waves travels one quarter of its own length from the front surface of the coating to the front surface of the lens. Then it travels another quarter of its own length to leave the surface after being reflected from the front surface of the lens. This is an important concept if we are to understand how an anti-reflective coating works. A light wave has now traveled one half of its own length, thereby reversing itself against the next one and the one before it. The waves create destructive interference and cancel each other.

Light transmission of different lens materials with and without AR coating

        Without AR      Without AR         Without AR         AR

Since one coating layer is precisely matched to eliminate one wavelength, other wavelengths (or colors) are not eliminated completely. By adding additional layers of coatings to the surface, additional wavelengths can be eliminated. This becomes a complex formula best completed by computer. Each manufacturer has a formula which is proprietary and felt to be their edge in this competitive market. When measured on a spectrophotometer, each of these individually formulated coatings appear differently and become the AR coating “fingerprint” of that manufacturer.

Every AR coating exhibits some residual color seen in the reflections of even a multi-layer coating. The color is significantly less in a multi-layer coating as compared to a bi-layer coating, however. The variations in color and intensity sometimes helps to identify the manufacturer of the coated product.

If a five layer coating is better than a two layer coating, does that mean that a 20 layer coating would be better still? AR coating efficiently is not directly improved by the number of layers, so much as by what each layer contributes to the reduction in reflection. Once again, the formulation of types and thickness of each material to be used in the five layer matrix becomes the priority in this very highly technical area of optics.

In fact, it is only due to refinements in both coating equipment and computers used to run them that these multi-layer coatings can be enjoyed by the Patients. The actual process of AR coating has evolved significantly over the last 50 years and is truly a state-of-the-art “high tech” process which utilizes a vacuum deposition technology. Modern AR coating equipment has been known to cost between $500,000.00 and $1,000,000.00.

Keeping lenses free of smudges and spots is a daily nuisance.
The process includes a hydrophobic/oleophobic layer applied
to the exterior of both sides of the lenses, which creates a
protective shield that repels water, dirt, dust and even oils.
This super smooth surface helps to keep lenses cleaner.



The photos above are of a drop of water on top of of two lenses,
one with AR and the other uncoated. Notice how the droplet on
the left actually"beads up" or repels the water as the surface
tension is removed by the AR coating, while the uncoated
lens on the right actual pulls the water toward the surface
of the lens. The same is true for dust dirt and even oil. Also
notice how the surface of the uncoated lens is much
more visible that that of the uncoated lens.

To begin the coating process, lenses must be carefully inspected for scratches or surfacing imperfections. Lenses are thoroughly cleaned to ensure good adhesion of the coating to the surface of the lens. Sophisticated ultrasonic cleaning processes are used by most coating companies, which utilize many cleaning and rinse cycles.

Once thoroughly cleaned, the lens is inspected once again to make sure that it has been properly cleaned (if a wax has been applied to hide lens imperfections this cleaning will remove the wax, highlight the scratches and make them more visible after coating). Rejected lenses will be returned to the lab to be remade.

The lens is placed in a degassing oven to assure that all moisture has been removed. This is an important step to make the coating process faster and efficient.

A typical vacuum coating machine has a rotating lens rack at the top of the unit. A monitoring device measures coating thickness. The machine actually measures the change in the frequency of an oscillating quartz crystal. The frequency of the crystal changes as the coating builds on its surface. Optical monitors can also be used in some cases. As the coating builds with the oscillating quartz crystal, the mechanical energy is changed to electrical energy and is fed into a computer for precise layer thickness. The composition and formulation of the materials evaporated onto the lens are proprietary. An electron beam gun evaporates the material to be used in the coating application. Vaporized molecules travel through the chamber to adhere to the lens surface. In a multiple layer coating system the computer controls the time and sequence of the deposition of coatings per side during operation.

A microscopic view of a typical AR coated surface shows very porous and bumpy areas in which oils and debris can accumulate on the last hard AR layer. Lenses seem dirty, oily and smudgy as a result of this porosity. A significant enhancement to the AR coating process is the application of an additional layer to fill in this porous material to provide a smooth, slick surface. This aids in abrasion resistance and makes the lenses easier to clean than any uncoated lenses. After the hydrophobic coating application the lenses are annealed for a tight chemical bond. As many of you know, AR coating with a hydrophobic coat make the lenses much easier to care for and as with AR coating–the hydrophobic coating will continue to be improved.

Preparing lenses for AR coating

Inspection and Cleaning

Before being sent to the coating lab, the lenses must be thoroughly cleaned and inspected in your office. A slight blemish or scratch which may go unnoticed on an uncoated lens becomes much more visible once the lens is coated. It’s best to inspect the lenses under a bright light, such as a halogen lamp, to get an idea what the lenses will look like after coating.

The lenses are inspected again by the lab, then thoroughly cleaned with alcohol to remove any markings or dried edger material. In the coating lab, the lenses are subjected to a series of ultrasonic baths which make them “raw” so they can accept a base to which the AR coating can adhere. The lenses are then baked in an oven to remove any excess moisture, since excessive moisture can cause adhesion problems. Finally, the lenses are placed in a vacuum chamber for the coating process where a layer of binding material, either chromium or silicon monoxide, is applied to the lens surface.

Know your lenses. Virtually any lens can be AR coated, including laminates and photochromics. However, AR coating does affect the changeability of photochromics slightly. Lenses should always be coated in pairs to avoid slight variations in residual color.

It’s best to provide the coating lab with ample information about the lenses including, lens material, manufacturer, color, and any in-office treatments you’ve applied including UV dye.

Tips for cutting and edging
lenses that are to be AR coated

Organize edging jobs so that all like materials are cut at the same time, i.e., don’t cut CR39 after a glass job.

Avoid cutting plastic lenses on a glass edger.

Wash you system down with water spray to remove any lens material remaining on the machine.

Use separate coolant buckets for glass and plastic jobs.

Be certain chuck pressure is correct when lenses are edged.

Change chuck pads when changing material.

Use surface-saver tape when edging, edge-polishing or grooving then remove the tape immediately after processing.

Be sure lenses are free from any kind of edger slurry and that they are free from layout marks before shipping to the coating lab.

AR coated lenses
Cosmetic considerations

Edge Polishing

Edge polishing should be done before the lenses are coated. Although the lens edges are not coated, any reflections that come through the edges are usually minuscule. While edge polishes and AR coating can work well together, both a polished edge and a frosted sample should be demonstrated to the Patient.

Tinting

If the lenses are going to be tinted, this must be done before being sent to the AR lab. Cosmetic tints reduce light transmission slightly, counteracting the purpose of AR. Coating the lenses makes them virtually invisible, tints make them visible again. Also, the color may not exactly match the sample since AR coating has its own residual color. For best results tint the lenses about 15% darker, then bleach out the excess color until it is about 5% to 10% darker than the end result you want. This will remove any surface dye and stabilize the color. UV treated lenses can also be AR coated. The back surface of sun lenses are often tinted to minimize reflections from light coming from the side or back of the wearer.

Selecting an AR coating laboratory

Lenses can be sent directly to a coating lab or they can be sent to the surfacing lab who may act as a middleman. The performance of the lab can be as important as the performance of the coating since customer service is critical to your success. Any questions you might have regarding AR coating should be answered quickly and politely. The cost of having lenses coated will vary according to the type of lenses being used, whether one side or both is being coated, and the amount of work the lab does for you.

Most AR coaters provide same day turn-around within their labs, which means three business days when transportation time is factored in. The coating lab should be able to provide support in an effort to educate Patients about the benefits of AR coating, and the Dispenser with marketing support such as point of purchase materials, and with the technical aspects of dispensing AR.

Presenting AR coating

The Refractionist can play an important role in presenting AR coating. The discussion of AR should begin in the exam room and be seen as an opportunity to educate Patients on the benefits of AR. Lifestyle information can be gathered verbally, or when the Patient completes a questionnaire. Either method can be used as a lead-in to presenting information about AR coating, or any other premium lens product such as high index materials or aspheric's. AR coating could be written on the RX, and it should be worn by the office staff.

After the exam, the Patient should be introduced to the Dispenser and the Refractionist may explain any lens options that were discussed with the Patient. If the Patient has selected high index lenses AR coating is especially important since high index materials reflect more light than conventional lenses. Many Practitioners coat the back surface of sunglass lenses to minimize reflections when the sun is located to the side or behind the Patient’s head. AR coated photochromics can improve light transmission at night while reducing back surface reflections.

Demonstration kits can be used when presenting AR coating to the Patient. The cosmetic benefits of AR can be easily demonstrated by placing two plano lenses in an attractive frame, one AR coated and the other not. The Dispenser should place the frame on the Patient and point out the cosmetic appeal of the coated lens. An especially effective method of demonstrating improved contrast enhancement of AR coated lenses is to hold a partially coated lens over printed material. The coated portion of the lens will produce a sharper crisper image.

When pricing AR coating, many Practitioners “bundle” the cost of AR into the lens price and consider it an integral part of the lens choice.

Provide excellent customer service with personalized attention and concern for ascertaining the needs of your Patient, then using your professional expertise to help them fill those needs.

Finally, its important to educate Patients on the proper care and maintenance of their AR coated lenses. Some suggestions for a Patient Handout on the care and maintenance of AR coated lenses follows.

Frequently asked questions about AR coating

Should AR coating be applied to Transitions lenses?

Yes. The AR coating creates an oxygen barrier and prolongs the life of the lens. Normally, without AR coatings the photochromics could break down as much as 22-23% after two years. With AR coating, the maximum break down is 16%. There is no loss in speed of activation and there is minimal-insignificant speed of fade with an AR coating.

Do AR coatings have any UV protection?

No. AR coatings do not contain any UV protection.

Can lenses be tinted after they have been AR coated?

No. Tinting needs to be done before the lenses are AR coated.

Patient handouts are recommended
How to Take Care of AR Lenses

AR coatings, as they are called, virtually eliminate the reflections, such as images of your own eyes and eyelashes, from the back sides of lenses. AR coatings also let more light reach your eyes through the front side of the lenses, increasing contrast and clarity. This means that you actually see better - particularly in such low-light situations as night driving.

AR coating will also significantly reduce light reflections from the front of lenses, making them seem almost invisible. People will focus on your eyes, not on your eyeglasses, and when appearing in photographs or on video, your eyes will become a lot more visible

Clean your new lenses carefully.

Just as your fine jewelry or delicate camera lenses must be cared for properly, AR coated lenses also need a little TLC so that they can continue to perform well.

AR cleaning tips

Rinse the lenses under the tap with lukewarm water.

Place a drop of a mild hand soap or dishwashing liquid on each lens. (Dawn and Joy are ideal. Don’t use soap that contains hand cream - this will smear the lenses.)

With your fingers, rub the soap on both sides of each lens for about 5 seconds per lens, then rinse under the tap.

Use a clean, lint-free cotton towel or a special microfiber cloth available from your optical dispensary to gently wipe each lens dry. Wash your microfiber cloths once a week, without a fabric softener to avoid an accumulation of body oils.

Do not “polish” your lenses - just remove the water. Avoid using most tissues or paper towels. Paper products are made from wood and may contain small particles that can scratch your lenses. Use care in using any cloths also, because the weave may be rough enough to scratch the lenses.

Clean your lenses at least once daily.

When there’s no water

If you need to clean your AR lenses when you do not have access to running water, you will need to take certain precautions to ensure that you do not scratch the lenses:

Use a spray cleaner that is specially formulated for AR lenses, thoroughly wetting each side of the lens and wiping them dry with a microfiber cloth.

Never attempt to clean your AR lenses dry if there is visible dirt on them. Rubbing the lenses while they are dirty may scratch them.

If the lenses are not dirty, only smudged, as with a fingerprint for example, use the special AR microfiber cleaning cloth to gently remove the oils.

Common sense

Use common sense to care for your glasses when you’re not wearing them to protect your lenses:

Keep your glasses in their case when they’re not on your face.

If you remove your glasses from time to time during the day, place them in their case. If you can’t keep your case handy, be sure that you do not rest the glasses face-down on the lenses. Also, keep the temples unfolded (just as they are when you remove them from your face) so that the temples do not meet the lenses and scratch them at the contact points.

Rest the glasses upside down on a flat surface. This will reduce their chances of tipping over onto the lenses and scratching.