عینک eyewear

In chemistry, hydrophobicity (from the Attic Greek hydro, meaning water, and phobos, meaning fear) is the physical property of a molecule (known as a hydrophobe) that is repelled from a mass of water.

hydrophobicity: noun; the property of being water-repellent; tending to repel and not absorb water / Synonyms for hydrophobic: aquaphobic, water repellent

Do scientists think water is wet? [8]

Water is not wet because wetness arises from the interaction between a liquid and a solid surface. In other words, wetness is a property that occurs when water or another liquid comes into contact with a solid object.

Hydrophobic molecules tend to be non-polar and, thus, prefer other neutral molecules and non-polar solvents. Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.

Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar from polar compounds.

Hydrophobic is often used interchangeably with lipophilic, "fat-loving." However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions—such as the silicones and fluorocarbons.[1]

A superhydrophobic coating is a thin surface layer that repels water.

It is made from superhydrophobic (ultrahydrophobicity) materials. Droplets hitting this kind of coating can fully rebound.

Superhydrophobic surfaces, possessing a high water contact angle (> 150°) and low sliding angle (< 10°), have attracted considerable attention because of their high water repellency and attractive self-cleaning, anti-corrosion, anti-icing, and anti-fouling properties.[4]

Thin layers of a waterproof substance on the surface of hydrophilic materials. Hydrophobic coatings are often called water-repellent, which is incorrect, since the water molecules are attracted to the coatings, although extremely weakly, rather than repelled by them.

Hydrophobic coatings are produced in the form of monomolecular layers (adsorbed orientated layers one molecule thick) or lacquer films by treating a material with solutions, emulsions, or less frequently, vapors of hydrophobic agents, which are substances that interact weakly with water but attach themselves firmly to a surface. Substances used as hydrophobic agents include salts of fatty acids and such metals as copper, aluminum, and zirconium; cation-active surface-active agents; and low-and high-molecular-weight organosilicon and organic fluorine compounds.

Hydrophobic coatings protect various materials (metal, wood, plastics, leather, and fabric and nonfabric fibrous ma-terials) from the destructive action of water or wetting. They are used particularly extensively in machine building,construction, and textile production.[2]

If you live in a cold climate, nothing is more frustrating than having your eyeglasses fog up when you come in from the cold. This also can be a safety issue, since it limits your ability to see until the fog clears. Lens fogging can be especially dangerous for police officers and other first responders to emergency situations. eResearch by Navid Ajamin -- spring 2012

At least one eyeglass lens coating company (Opticote) has created a permanent coating designed to eliminate this problem. The factory-applied coating — called Fog Free — eliminates the condensation of moisture on lenses that causes fogging.

So your lenses and vision stay clear when you make the transition from a cold environment to a warm one. It may also keep your lenses from fogging up during sports and other times you are hot and perspiring.

Fog Free can be applied to plastic, polycarbonate and other eyeglass lenses, including high-index lenses and Transitions photochromic lenses. The anti-fog coating is applied to the lenses before they are cut to fit into your frame at the optical lab. Ask your optical retailer about pricing and availability.

Fire ants can cluster together to increase their buoyancy – a property that scientists hope to copy to clean up oil spills -- superomniphobic surfaces

In October 2011, Essilor introduced a line of eyeglass lenses called Optifog, which the company describes as "a breakthrough lens with an exclusive anti-fog property."

The anti-fogging property of Optifog lenses is activated by applying a drop of Optifog Activator to each side of the lens, then wiping the lens with a microfiber cloth to thoroughly spread the liquid across the entire lens surface. This treatment keeps the lenses fog-free for up to one week, according to Essilor.

Lens fogging is caused by tiny water droplets that form by condensation on the surface of eyeglass lenses when the lenses are significantly cooler than the surrounding air temperature. Optifog works by uniformly spreading these water droplets across the lens surface so they become invisible, Essilor says.

What is hydrophobic cloth? [6]

Hydrophobic nonwovens are used for products that are intended to provide a dry barrier, while withstanding moisture. Some fibers, such as polyester, naturally have hydrophobic characteristics. In other cases, coatings and treatments can be used to make hydrophobic material from naturally absorbent fiber like cotton.

What is an example of a hydrophobic material? [7]

Hydrophobic molecules are molecules that do not have a charge, meaning they're nonpolar. Hydrophobic materials often do not dissolve in water or in any solution that contains a largely aqueous (watery) environment.

Oil, waxes, and steroids are all examples of hydrophobic materials and molecules.

Optifog lenses are available in plastic, polycarbonate and high-index plastic lens materials, with or without Essilor's proprietary Crizal anti-reflective coating.[3]

Reference:

1. en.wikipedia.org/wiki/Hydrophobe
2. encyclopedia2.thefreedictionary.com/Hydrophobic+Coatings
3. allaboutvision.com/lenses/coatings.htm
4. sciencedirect.com/science/article/abs/pii/S0927775721018422
5. chemistryworld.com/features/superhydrophobic-materials-from-nature/3010321.article
6. wptnonwovens.com/blog/hydrophobic-material-vs-hydrophilic
7. study.com/learn/lesson/hydrophobic-effect-molecules-examples.html
8. clearlyfiltered.com/articles/is-water-wet

Many people spend a large amount of time in the office just dealing with computers. It is not few to see white-collar workers to have all kinds of problems relating to eyes. Maybe they just use their eyes too often. But that is really unjustified. Everybody uses their eyes everyday and no less often than the white-collar workers. The problem lies in the computer screen. Many people say the LCD has less radiation, but the problem is the radiation is always there. In order to solve the problem, a lot of methods have been tried, such as place a plant near our computer, but the result is not satisfactory. Actually, wearing computer glasses is the best and easiest way to fight against computer radiation. There might still be some left, but very little. Many people are against the idea that computer glasses can absorb computer radiation. Many of their ideas are unfounded. Here let’s review something that is of vital importance relating to computer glasses. eResearch by Navid Ajamin -- winter 2012

Why Are Computer Glasses Lenses Anti-radioactive?

Essentially, computer glasses lenses are totally different from general prescription glasses in the way that the lenses are designed. The lenses have been coated with anti-radioactive coatings that have been added with some compound medium. Computer radiation comes from electromagnetic wave that has certain wavelength and amplitude. The working of anti-radioactive coatings has been based on the working theory of the electromagnetic wave, which the amplitude (if two amplitudes are the same) will be strengthened when the wavelength is the same and offset when the wavelength is opposite. Based on this theory, the computer glasses lenses have been coated with many anti-radioactive coatings to generate electromagnetic waves that are of different wavelength to intervene one and another and thus reduce computer radiation.[1]

If you work at a computer for a significant amount of time each day, you may benefit from a pair of special reading glasses known as computer glasses. Even though you wear glasses or contacts on a daily basis, they are probably not quite right for your work at the computer. Computer glasses are special glasses prescribed to lessen the symptoms associated with computer vision syndrome (CVS). CVS describes a group of symptoms caused by prolonged computer use. Symptoms appear because the eyes and brain react differently to words on a computer screen than they do to printed text. Symptoms often include eyestrain, dry eyes, headaches and blurred vision. Many people try to compensate for these vision problems by leaning forward or by looking down to see through the bottom portion of their glasses, often resulting in back and shoulder pain.
Symptoms of CVS can also be caused by presbyopia, a vision disorder that develops as we age. Presbyopia is the loss of the eye's ability to change focus to see near objects, and usually becomes noticeable around the age of 40. If you think you might be feeling some of the symptoms of CVS, you may need to purchase a pair of computer glasses. Computer glasses are prescription glasses specially designed to allow patients to work comfortably at a computer. Computer work involves focusing the eyes at a close distance. Because computer monitors are usually placed a little further away than a comfortable reading distance, standard reading glasses are usually not enough to alleviate symptoms of CVS. With computer glasses, the whole lens focuses at the same distance and does not require you to tilt your head back to see the computer screen.[2]

"Children are vulnerable because they have large pupils and pristine lenses," said Barnes. "The American Academy of Pediatrics states that no child under the age of two years should be on any computer device. And I would extend the limitation to children five years of age."

Blue light is emitted by computer screens, laptops, notebooks, tablets, smart phones, LED lights and television screens.

Blue light is the shorter wavelength of light called High-Energy Violet light or HEV. The most damaging HEV Wavelength is between 400 and 420 nanometers (nm). This is the most harmful wavelength to the retina, causing macular degeneration or macular re-modulation.

Computer glasses for kids are specially designed to block blue light from digital devices. Giving your children blue light blocker glasses will virtually eliminate the effects of digital eye strain and significantly reduce the risk of AMD and other retinal degenerative diseases.

Blue light has been linked to all sorts of issues, from causing digital eye strain to making us blind. There's a lot of conflicting evidence, however, about exactly how harmful (or not) it really is.During daylight, blue wavelengths of light can be beneficial, playing an important role in setting circadian rhythms, boosting attention and mood. But we didn’t evolve to be exposed to it as much as we are. In addition to the ample blue light in sunlight, most of the light we are exposed to via digital devices is also blue. For example, the most common type of LED used in electronic devices is a white-light LED, which actually has a peak emission in the blue wavelength range (400 – 490 nm). Moreover, the eye’s cornea and lens are unable to block or reflect blue light.

Increasing evidence suggests that blue light has a dark side. At night, it can suppress the secretion of melatonin and wreak havoc on our circadian rhythms, and recent studies have shown that extended exposure to blue light can damage the retina, though exactly how it does this has not been clear.

Now, new research from the University of Toledo demonstrates that when blue light hits a molecule called retinal, it triggers a cascade of chemical reactions that could be toxic to cells in the retina of the eye.

Reference:

• buyeyeglasses.pythonblogs.com
• vision.about.com
• globenewswire.com
• forbes.com

There are over 143 million adults in America who wear glasses. Many of these adults opt to have an anti-reflective coating applied to their lenses for a variety reasons. Anti-reflective coating not only improves the appearance of the glasses but also the vision seen through the lenses. Additional benefits of anti-reflective lenses include durability, heat resistance, aid in night driving, easy cleaning, and resistance to scratches.

The highest quality anti-reflective coating has a hydrophobic, or water-resistant, layer that is made to prevent water spots from developing on the lens and also makes them much easier to clean. Some anti-reflective coatings also have an oleophobic, or oil-resistant, layer that resists oil from the skin and once again makes it easier to clean smudges off of the lenses.

Today, anti-reflective coatings have even become very popular with sunglasses. When applied to the backside of the sunglass lenses, anti-reflective coating reduces the reflections of the sunlight into the eyes when the sun is coming in from behind.

There are many reasons why an anti-reflective coating is added to the lenses of a pair of glasses or sunglasses. This coating is often chosen for appearance, as it improves transparency and reduces the reflections in the glasses. The anti-reflective coating on lenses makes it easier for a glasses wearer to have direct eye contact with someone else without all of the distractions of reflections.

The anti-reflective coating helps improve driving safety, especially at night, by eliminating distracting headlights and streetlights. This allows drivers to focus more on the road.

Also, while working, the unnatural and artificial lights found in many offices can quickly cause eye fatigue.

Using a computer likewise puts great strain on the eyes. Having an anti-reflective coating applied to lenses will help to protect the eyes while working.

Last but not least, an anti-reflective coating on a lens enhances the quality of a lens and also lengthens its lifetime by providing durability and resistance to water, dirt, and scratches.

The problems glare can cause

So, why do we care about glare? Well, it can present numerous problems for wearers, especially when driving, playing sports and working with computers and other tech with direct light sources. The result is inhibiting vision and attributing to health issues, including eye strain, blurred vision or ‘halos’ around bright lights such as street lamps, headaches, migraines and a significant decrease in concentration and focus when squinting to avoid glare. On the odd occasion, it may not seem like a priority to have anti-glare, but once these health issues become chronic, you can have very real, very uncomfortable health issues to deal with.

Do I need anti-glare lenses?

Anti-glare lenses are suitable for everyone, especially in our predominantly digital workspaces, working from home, TV streaming and internet heavy lives we lead. And while some people suffer from the effects of glare more than others, the exposure to digital screens and then natural light to take a break from them will only ever increase. Computer screens, driving at night, and sun exposure are all very different scenarios that can be marred by the effects of glare. And while AR coating does not guarantee reflection elimination, wearing anti-glare lenses will reduce fatigue in your eyes and headaches as a result by lessening the amount of reflection and light coming through your lenses.

Anti-glare coating is layered on both the front and back end of a lens, designed to manipulate incoming light. It allows your eyeglasses to provide you with optimal vision. An anti-glare coating is incredibly effective when applied, blocking up to 99.5% of incoming light. This makes reflections practically invisible. eResearch by Navid Ajamin -- winter 2011

Glare in your eyes can be hazardous to you and everyone around you. It can obstruct your driving at nighttime and during the day. UV light can be damaging to your eyes as well—too much exposure can lead to diminishing eyesight, dryness, and loss of elasticity.

Reference:

• justeyewear.com
• lensology.co.uk/what-are-anti-glare-glasses
• eyeeffects.ca/what-do-anti-glare-glasses-do

Photochromic lenses are lenses that darken on exposure to ultraviolet (UV)radiation. Once the UV is removed (for example by walking indoors), the lenses will gradually return to their clear state.

fow·tow·krow·muhk photochromic /ˌfəʊtə(ʊ)ˈkrəʊmɪk/

Photochromic lenses may be made of glass,polycarbonate, or another plastic.

Photochromic lenses are eyeglass lenses that are clear (or nearly clear) indoors and darken automatically when exposed to sunlight. Other terms sometimes used for photochromic lenses include "light-adaptive lenses," "light intelligent" and "variable tint lenses." [6]

Are photochromic lenses good for eyes?

One of the key advantages of photochromic glasses is their 100% protection against harmful UVA and UVB rays. This built-in UV protection helps prevent long-term eye damage, such as cataracts, photokeratitis, and skin damage.

Manufacturers create photochromic lenses from various materials, with plastic being the most common in modern eyewear.

The base lens material is typically one of the following: [5]

1. Polycarbonate: A popular choice due to its impact resistance and lightweight properties.
2. High-index plastic: Offers a thinner profile for higher prescriptions.
3. Trivex: Combines impact resistance with excellent optical clarity.
4. CR-39 plastic: A standard plastic lens material with good optical qualities.

The photochromic molecules are then incorporated into these base materials using different methods

Early photochromic glasses were usually made of glass and contained small crystals of silver halides (e.g., silver chloride) that darkened when exposed to light, just like old photographic films.

The glass version of this type of lenses was first developed by Corning in the 1960s. More recently, plastic versions of these lenses have been commercialized. The first of these was the Photolite lens sold in the early 1980s by American Optical Corporation, but the first commercially successful plastic photochromic lens was introduced by Transitions Optical in 1991. [1]

Notice how the molecule on the left gets rearranged when exposed to UV light (Photo Credit : American Chemical Society Publication)

Photochromic properties of iron-added BaMgSiO4 -- aist.go.jp

However, unlike those films, the darkening of photochromic lenses was reversible, i.e., the lenses became clear again once the ambient light was lowered. The crystals used in the glass of such lenses were minuscule, both in number and size. Fewer than 0.1% of silver halide crystals, which were 100 times thinner than a human hair, were used in early photochromic glasses.

Modern photochromic glasses, however, are usually made of plastic, rather than glass, and contain carbon-based (organic) molecules instead of silver compounds. Such compounds are better, more efficient alternatives for achieving the quick-darkening and quick-clearing effect, as their molecular structure varies in accordance with the presence/absence of a certain type of light (usually ultraviolet light, as it’s a component of sunlight).

The most commonly used photochromic molecules are naphthopyrans and oxanes, due to their ability to change their molecular structure reversibly upon exposure to UV light.

Who should wear photochromic lenses? [5]

Photochromic lenses are suitable for a wide range of users, including:

• People who frequently transition between indoor and outdoor environments.
• Individuals sensitive to light or prone to eye strain, including presbyopes.
• Those who want convenient UV protection without carrying multiple pairs of glasses.
• People who engage in outdoor activities but don't want to switch between regular glasses and sunglasses.
• Children and teenagers, as their eyes are more susceptible to UV damage.

Photochromic lenses, such as Transitions®, quickly adapt to changing light conditions. The lenses darken in outdoor light, reducing glare and providing 100% UV protection, then quickly become clear again when you're inside, giving you comfortable vision, both indoors and out.[2]

Transitions is actually a brand name of a Photocromic Lens. Although transitions are probably the most advanced photochromic lens on the market there are many others out there.

People call Photochromic lenses by all different kinds of names such as Transitions, Reactolite, Reactions and I've even heard them called Graduations. However, they are all Photo chromic lenses.

Photochromic lenses are clear lenses that react with UV and produce a tint effect based on the amount of UV present.

When wearing Photochromic lenses even a dull day some reaction will occur producing a very pale tint and then on a very bright day where more UV is present they will turn quite dark. When wearing them indoors they will become clear. eResearch by Navid Ajamin -- spring 2011

The idea behind photochromic lenses is that they will provide the correct amount of protection for the varying light conditions you experience. However, when driving, your car windscreen will block a certain amount of UV which is required to make the lens react so they will not work as well as they would outside of the car.

The Two Most Common Photocromic Lenses

Transitions Lenses

Transitions are available in Standard Plastic, Poly Carbonate, 1.6 and 1.67 Lenses. They are the fastest reacting lens on the market and will react into sunglasses within 30 seconds. However, they will take longer than that to go clear again when you go inside.

Reactolite Lenses

Reactolite is a brand name given to a Glass photochromic lens. They do not react as well as the transitions and are much heavier to wear. However, one good thing about glass reactolite is that they work much better behind a car windscreen than the transitions do. (If only we could have the best of both worlds.)

In most cases the Transitions lens is the preferred option due to the over all comfort and performance.

Photocromic lenses are ideal in the sense that they can save you having to purchase two pairs of glasses ie, Clear glasses and a pair of Sunglasses. However, many people who wear transitions also have a cheaper tinted pair just to use in the car.[3]

Reference:

1. en.wikipedia.org/wiki/Photochromic_lens
2. chappleopticians.com/pages/glasses/lens-options.php
3. ezinearticles.com/?Pros-and-Cons-Of-Photochromic-Lenses&id=891841
4. scienceabc.com/innovation/how-do-photochromic-photochromatic-glasses-work.html
5. iotlenses.com/blog/what-are-photochromic-lenses-and-their-benefits.html
6. allaboutvision.com/lenses/photochromic.htm

See also:

• Photochromic lenses explainthatstuff.com
• How Do Photochromic (Photochromatic) Glasses Work? scienceabc.com
• The History and Future of Smart Photochromic Technology transitions.com

Eyeglasses in various types have different benefits. Prescription eyeglasses are mainly for vision correction and sunglasses are particularly designed to offer protection from UV light. Some people simply wear eyeglasses for a stylish look. Currently eyeglasses are available in a variety of lens materials and frame materials. There are also some lens coatings such as anti-reflective(AR) coating and scratch-resistant coating and so on.

One of the common concerns from eyeglass wearers is that whether anti reflective coating is necessary. In general, the answer is yes. This coating applied on lenses can prevent excessive light from entering the eye. Without proper control of the intense light, the pupil will experience unnecessary strain. eResearch by Navid Ajamin -- spring 2010

Having AR coating on your lenses does not only enhance your look, but they are also beneficial for:

• Reducing glare and reflections.
• Reducing glare at night when driving.
• AR coating helps prevent “digital eye strain” for individuals who work in front of computers all day.
• Enhancing the appearance of your glasses.
• Making the lens appear invisible.

Another advantage of anti-reflective coating is that it can address the problem of halo effect around the headlights of the opposite vehicles during night driving. This effect is quite dangerous because the vision can be distracted. Anti-reflective coating on a lens can effectively deal with this problem.

Computer users can also greatly benefit from lenses with anti-reflective coating. Regular computer users have probably experienced the bothersome glare from special parts of the PC monitor. They are forced to strain the eyes in order to get clear vision, which may lead to irritation or dry eyes. Anti-reflective coating performs well in eliminating glare. Anti-reflective coating is also believed to reduce eye pressure in dim light conditions.

In addition, eyeglasses with anti-reflective coating are particularly favored by individuals who like taking photographs. A disappointing defect of ordinary eyeglasses is that the outside images will hide the eyes while taking a photo. Anti-reflective coating can effectively block out the reflected images. This feature is very exciting and handy for photographers.

On the other hand, glasses with anti-reflective coating also need special care. While offering those benefits described above, anti-reflective lenses are easy to scratch, pick out fingerprints and become dirty. Wearers should use special cleaning tools, rather than ordinary cloth that may cause scratches.

Benefits of Anti-reflective Coating

Many people who wear anti-reflective coating glasses find them to be helpful in the following ways:

1) You see less glare on your vision, making it easier to see in environments where light is present.

2) Helps reduce eye strain by blocking treats conditions such as nearsightedness.

3) Anti-reflective coating glasses will provide better protection from the sun's rays and harmful UV light than regular eyewear.

4) Some people wear anti-reflective coating glasses and prescription lens to reduce the glare of computer screens or for reading in bright environments.

5) Prevents eye fatigue by blocking high-energy visible light, which causes it.

6) Helps protect your eyes from UV rays, glare, and other issues related to the sun.

7) The glare is eliminated, making it more comfortable to work on screens for long periods of time.

8) The lenses on the glasses can be easily removed for cleaning, which keeps them from getting dirty and makes your vision clearer.

9) Anti-reflective coating reduces any level of reflecting that might happen when you're looking at a light source like a computer screen or television.

10) It helps to reduce the amount of glare that you see when looking at a window or other reflective surface.

11) Anti-reflective coating lenses are much cheaper to replace than prescription glasses, making them more accessible for those who might not otherwise be able to afford them.

12) They can help you focus on details better than ordinary eyeglasses would be able to do. This makes them great for use in low light conditions or when doing detailed work such as working with small objects like jewelry or electronics.

13) They keep their eyes from drying out. This is because they allow less light into their eye and are often made of materials that reduce friction on the eyeball, which can cause dryness.

14) They generally have a wider field of view which is excellent for people who wear glasses to see things at a distance, such as driving or watching television.

15) They don't need to be cleaned often because they have an anti-reflective coating that prevents smudges and makes it easier to clean them with water when necessary.

Reference:

• articlesbase.com
• bella-eyecare.com/eyeglasses/why-you-should-get-anti-reflective-lenses
• rx-able.com/blogs/blogs/benefits-and-disadvantages-of-anti-reflective-coating-glasses

Enhanced High Resolution Vision™ with flexible wearing parameters

Designed with Essilor’s exclusive W.A.V.E Technology™ Varilux Physio f-360º goes beyond High Resolution Vision. Taking into account five key wearing parameters – left and right pupillary distance, left and right vertex distance, fitting height, pantoscopic tilt and wrap angle – Varilux Physio f-360º provides superior visual performance whatever the gaze direction.

Features and Benefits

Flexible fitting parameters

Vx Physio f-360° takes into account five key wearing parameters for optimal visual performance

1. Left and right pupillary distance
2. Left and right fitting height
3. Left and right Vertex distance
4. Pantoscopic tilt
5. Wrap angle

Varilux Physio f-360° is a customized lens, designed to meet each wearers exact requirements. By analysing the impact of wearing parameters, the optimal wavefront can be defined for each wearer, resulting in up to 30% more natural vision.*

*Analysis done with comparison to standard Varilux plano +2.00 add lenses for the following wearing conditions: Vertex 12mm, Pantoscopic Tilt 2°, Wrap 14°.

NEAR vision: custom located

• Defocus lowered by 30%
• Up to 30% more natural vision thanks to a custom-located Near Vision zone defined by Essilor’s DPS (Dual Positions System™).
• The DPS (Dual Positioning System™) works in the same way as a Global Positioning System. GPS helps to determine the precise positioning of the car while the DPS ensures the perfect positioning of the near vision area individually for each wearer.

INTERMEDIATE vision: Astigmatism Control

• Unwanted astigmatism is lowered by 30%
• Axis directed vertically

FAR vision: Coma Control

• 30% reduction in higher order aberrations

Seeing the world better 

Reference: http://www.essilor.co.nz

Lenses today are available in a wide variety of material and designs. It’s our job to match the prescription and the patient’s visual needs with the best lens choices. To do this we need to know the different materials, their designs and be able to explain their features and benefits to the patient.

• Glass (Crown Glass)

• Plastic Hard Resin - CR-39

• Polycarbonate

• Hi Index Glass

• Hi Index Plastic

• Mid Index 1.53 (NEW)

• Mid Index 1.54 to about 1.58

• Hi Index 1.60

• Hyper Index 1.66

Glass (Crown Glass)

For years glass was the number one choice for lens materials. With the most precise and constant optics, glass is considered to offer the most natural and comfortable vision. Untreated glass is not resistant to breakage, therefore ANSI (American National Standards Institute) standards state that all glass ophthalmic lenses must be either heat, or chemically hardened to improve impact resistance. Many of the older glass seg styles and tints are no longer available, or are only available at a high cost. Some colors can be obtained by coating the lens, although the cosmetics involved are questionable. Glass lenses are spherical design only and considered to be old technology by most dispensers.

Features and Benefits: Excellent optics and the best scratch resistance of all materials. Remember, nothing is “scratch proof”. Fused segments meaning there is no lip on top of segment like all plastic materials have. Glass lenses take AR Coating excellently.

Negatives: Glass is the heaviest material available as well as the lens “most likely to break”. Glass also pits and scars when being used by welders. No aspheric designs available now, but they are coming. Tints in Glass lenses are built into the material, this includes glass photochromics. This will cause minus lenses to be darker around the edge and plus lenses to be darker in the center. To avoid this, use another lens material, or coat the lens for uniform density. Flat top bifocals and trifocals in glass photochromics are a different material from the rest of the lens and are clear, causing the bifocal portion to be lighter in color than the rest of the lens. There is no UV protection in clear glass lenses.

Plastic Hard Resin - CR-39

The number one lens choice in today’s optical market according to the sales numbers. Plastic’s excellent optics, comfortable abbe, lightweight, ease of tinting and durability make it the most common choice among dispensers. There are more lens styles and blank sizes available in plastic today than any other lens material. Improved scratch resistant coatings have helped sales and should always be recommended.

Features and Benefits: Plastic is roughly one half the weight of a comparable glass lens. Plastic will accept tints easier than any other material, it can be treated for UV, scratch coatings are available, takes AR and almost any other lens treatment available.

Negatives: While standard plastic is the most common lens sold today, it’s old technology, the equivalent of giving someone an AM radio that wants a good sound system. About 30% thicker than glass, plastic requires that scratch coatings and UV enhancements (at an additional cost), rather than being built into the material like the newer products. While available in aspheric design, the additional cost is the same as going to an aspheric designed Mid to Hi Index lens.

Polycarbonate

Most impact resistant of all lens materials used today, polycarbonate has been the best choice for safety eyewear, kid’s glasses and sports eyewear. Polycarbonate has the added advantage of being a natural UV filter, protecting to 380 nm UVA and all UVB. While it has one of the higher indexes, it has a low specific gravity making it lighter in weight than most other lenses.

The Optical Laboratories Association has a program called “Duty to Warn” available to help educate your patient on polycarbonate and their choices. Proper positioning (4-5mm below the center of pupil) on single vision, good frame selection (No more than 5mm of decentration per eye, preferably less) will help avoid problems. We recommend the addition of multi-layer AR coatings to help provide the best vision for the patient

Features and Benefits: The safest, lightest and one of the thinner materials available. New super tough scratch coatings can make this the most scratch resistant material available for a small added charge. Now available in aspheric designs that widen the viewing area to about that of a Mid Index lens.

Negatives: Many polycarbonate lenses do not tint as evenly, as dark, or as naturally as CR-39. Polycarbonate’s lower abbe number can result in more chromatic aberration than some other lenses. Proper fitting and aspheric design can correct this.

Refractive Index

Eyeglass lenses are often categorized by their refractive index (also called index of refraction).

The refractive index of any substance is the speed of light in that substance compared to the speed of light in a vacuum expressed as a ratio. Light travels fastest in a vacuum and slower through different materials.

Refractive Index = speed of light in a vacuum / speed of light in the comparative material

The refractive index of a basic plastic lens (CR-39) is 1.498 meaning that light travels 1.498 times faster in a vacuum than it does through the plastic lens.

The higher the index of refraction the thinner a lens can be to get the same refraction effect. Optical lenses are now classified into the following categories:

• Normal Index: 1.48-1.54
• Mid Index: 1.54-1.64
• High Index: 1.64-1.74
• Ultra High Index: 1.74 and above.

Abbe Value

Abbe value is a measure of the lens material’s dispersion of light. A lens with a low Abbe value causes a higher dispersion and leads to unwanted chromatic aberration. Chromatic aberration is a distortion of the image due to the inability of the lens to focus all colors onto the same focal point. This leads to the perception of undesirable color fringes when viewing objects for many people.

High index lenses offer a thinner lens but usually have lower abbe values. The Abbe value determines to a large part the optical integrity of the lens. The higher the abbe value the better the optical clarity and less distortion. It is a delicate balance to find a lens that not only satisfies in terms of aesthetics and weight, but also features acceptable optical clarity.

In the United States, most high index lenses are made from the various plastic materials. Some other countries still use a lot of glass material for high index lenses. Glass is available in very high indices such as 1.8 and 1.9 but because of its density it is still very heavy. Glass lenses also take longer for optical labs to fabricate. High index plastic lenses can be used in desired rimless and 3 piece mount frames.

Reference:

• mastereyeassociates.com/eyeglass-lens-materials
• comlyeyecare.ca/eye-health/2023/2/26/lens-materials-in-glasses

Photochromic lenses are the tint changing lenses in eyeglasses that darken when exposed to UV rays from the sun. With the many brands and styles available, these lenses combine fashion with comfort and offer protection from the damaging effects of UV radiation and glare while at the same time enhancing patients' quality of vision.

Why Photochromic
One of the problems facing those who wear corrective eyewear is how to protect their eyes from the glare of the sun. Not only is bright sunlight difficult to see in, excessive exposure to ultraviolet radiation can cause permanent damage to the cornea and conjunctiva of the eye.

Before the introduction of photochromic lenses, patients were forced to purchase a set of eyeglasses for indoor wear as well as a set of prescription sunglasses for outdoor wear, often having to carry both and switch when traveling from inside to outside.

Thanks to photochromic lenses, eyeglass wearers can now purchase one set of glasses that will allow them to see inside, as well as reduce the glare of the sun when outdoors.

Disadvantages of Photochromic Lenses

• Photochromic lenses get darken when coming in contact with the sunlight, blocking your windshields. Therefore, they are risky to wear while driving.
• These lenses are also affected by the weather. This means that it takes more time to get dark in the winters.
• Some photochromic lenses are not polarized, leading to harsh glares of sunlight. Therefore, make sure you ask the doctor about all the details of the glasses that you wear.

How Do Photochromic Lenses Work?

Regular sunglasses block out only a particular amount of wavelengths of light with polarization. But the photochromic lenses are carbon-based therefore, the molecules present in the lenses react to the UV, this leads to the change in shape as the lenses absorb the light and it seems to look darker. The darkness of the lens depends on the amount of light present, the brighter the light the darker the lenses. The darkening of the lens takes up to 30 seconds and it can take 2-5 minutes to get back to normal when an individual goes back to an indoor area.

As photochromic lenses protect our eyes from harmful UV rays, therefore, they are considered a safe option to keep our eyes healthy. These lenses are either made up of plastic, glass, or polycarbonate. Different kind of lens is prescribed to different people depending on the difficulties faced by them.

Who Should Use Photochromic Lenses?

Photochromic lenses can be worn throughout the day on the daily basis. They can be used just like normal eyeglasses. These lenses are beneficial to all and especially to those who continuously change from outdoors to indoors.

These lenses are highly recommended for children as they tend to spend much time playing outdoors, therefore it keeps their eyes safe from the sunlight.

How To Choose Photochromic Lenses?

Consult an eye care professional as he/she will guide and tell you all about the glasses which are prescribed to you. They will also help you to find the best eyeglasses that will work according to the requirement of your eyes. Consulting them might take some of your time from your busy schedule but it will surely lead to you being happier with the outcome.

These lenses are also known as “transitional lenses” as it adapts itself depending on the lighting conditions. It gets darken when exposed to bright light, protecting our eyes from harmful UV rays. There are certain benefits of using photochromic lenses over normal sunglasses as it adapts itself depending on the light conditions and you don’t need to carry multiple lenses with you. It has the property of both the normal lenses as well as the polarized lenses. But everything has its limits. These lenses are not safe to wear while driving as it blocks the windshields. These lenses are also affected by the weather which is again not a very good sign for eyeglasses.

Make sure you consult a doctor before choosing any lenses for yourself. As they will guide you about what is better for your eyes.

Advantages of Photochromic Lenses

• Helps in reducing eye strain and eye damage by blocking up to 100% harmful UVA/ UVB light.
• These glasses are very convenient to carry as you do not need different glasses for different lighting conditions.
• These lenses also protect our eyes from the high risk of cataracts by blocking out as much light as possible.
• Photochromic lenses are cost-effective. It has the feature of both the lenses (normal lens and sunglasses).
• These lenses are available in different shades, tints, and styles suitable for your taste.

Are photochromic lenses suitable for driving?
Answer: Photochromic lenses work in UV light, which most car windscreens block out. As a result, they tend not to react as quickly in a car as they would normally. Tinted glasses, lenses or visors should not be worn at night or in poor visibility, but are fine to use in good driving conditions.

What is the difference between photochromic and transition lenses?
Photochromic or "adaptive" lenses darken when exposed to UV light, such as when you walk outdoors. When you are no longer exposed to the effects of UV, (i.e. walk indoors), the lenses return to their clear state. Transitions lenses are photochromic lenses that block 100% of harmful UVA and UVB rays.

Photochromic eyeglass lenses, also known as Transitions™ lenses, are lenses that change colour based on the amount of UV light they are exposed to. They are a popular choice for people who wear glasses and want to have both prescription lenses and sunglasses in one pair of glasses. However, like any product, there are pros and cons to using photochromic lenses.

Pros of Photochromic Lenses

• Convenience. One of the most significant advantages of photochromic lenses is their convenience. They can adjust to different lighting conditions, which means that you don't have to switch between regular glasses and sunglasses. This is especially beneficial for people who spend a lot of time outdoors, such as hikers or joggers.
• Protection. Photochromic lenses are designed to protect your eyes from harmful UV rays. This is important because exposure to UV rays can cause serious eye damage, including cataracts and macular degeneration. Photochromic lenses can block up to 100% of UV rays, which can help prevent these conditions.
• Style. Photochromic lenses are available in a wide range of styles, including prescription lenses, bifocal lenses, and progressive lenses. This means that you can get the right type of lens for your specific needs and preferences. Additionally, photochromic lenses are available in a range of colors, including gray, brown, and green.
• Cost-Effective. While photochromic lenses may cost more than regular lenses, they can be cost-effective in the long run. Instead of having to purchase two separate pairs of glasses (one with prescription lenses and one with sunglasses), you only need one pair. This can save you money over time.

Cons of Photochromic Lenses

• Activation Time. One of the most significant drawbacks of photochromic lenses is the amount of time it takes for them to activate. Depending on the brand and model, it can take up to several minutes for the lenses to darken in bright sunlight. This means that you may have to wait before you can comfortably see in bright sunlight.
• Temperature Sensitivity. Photochromic lenses can also be sensitive to temperature. In very cold weather, the lenses may not darken as much as they would in warm weather. This can be problematic for people who live in cold climates or who spend a lot of time outdoors in the winter.
• Limited Tint Range. While photochromic lenses are available in a range of colors, the tint range is limited compared to traditional sunglasses. This means that they may not be suitable for people who need a very dark tint to protect their eyes in bright sunlight.
• Replacement Cost. Photochromic lenses are more expensive than traditional lenses, which means that they can be costly to replace if they get scratched or damaged. Additionally, some insurance plans may not cover the cost of replacing photochromic lenses.

Reference:

• catalogs.com
• eyemantra.in/eyeglasses/photochromic-lenses
• luxyin.com/blogs/shopping-tips/quick-know-about-photochromic-lenses
• eye-deology.com/fyeyes/photochromic-lenses-pros-and-cons

See also: How do photochromics work? - Transitions Lenses

Types of Lenses and Coatings

Single-vision lenses

The simplest form of spectacle or contact lens is the single-vision lens, made to a single prescription to correct a particular eyesight problem. Concave lenses are used to correct short sight and convex lenses to correct long sight. Concave lenses are generally thinner in the centre than they are at the edge and convex lenses are usually thinner at the edge than at the centre. The curvature of the lens, its thickness and weight will depend on the amount of long or short sight it is designed to correct. The lens material will also influence the thickness and weight of your lenses, as will the size and shape of the spectacle frame you choose. Traditionally, spectacle lenses were made of glass but most lenses are now lightweight plastic and there is a wide range of materials available to suit your prescription and lifestyle.

Bifocals

Bifocal lenses contain two optical corrections with a distinct dividing line between the two parts. The most common use of bifocals is for people who have become presbyopic and need a different prescription for close work. The upper part of the lens corrects distance vision and the lower half is for near vision. Trifocals are also available that have three sections and incorporate a correction for intermediate vision. Bifocals and trifocals come in a range of designs but nowadays varifocal lenses are much more likely to be prescribed.

Varifocal or progressive lenses

Varifocal lenses, also known as progressive lenses, are used for correcting presbyopia but unlike bifocal lenses have no visible dividing lines between the different corrections. Instead they have a graduated section in which the power of the lens progresses smoothly from one prescription to the other, allowing the wearer to see clearly at all distances. These lenses also have the benefit of looking better - they don't draw attention to the ageing process. A range of varifocal designs is available depending on your lifestyle and occupation. Modern lens technology means that there are many different designs and materials to choose from. Your optometrists or dispensing optician will be able to advise you on the best lenses to suit your individual requirements.

High-index and aspheric lenses

If you need high-powered lenses you can improve the weight or appearance of your glasses with special lens materials and designs. High-index materials and aspheric designs mean that lenses can now be made thinner, lighter and better looking than traditional lens types. High-index materials make lenses for short sight thinner, while aspheric designs that minimise the amount of material make lenses for long sight both thinner and lighter.

Prescription sunglasses

Whatever your prescription, it is important to protect the eyes against excessive ultraviolet (UV) radiation. Protection is needed to avoid reflected light from sand and snow or if you spend long periods out of doors, particularly in the summer. Prescription sunglasses can be made with single-vision, bifocal or varifocal designs to offer the same standard of protection as non-prescription sunglasses.

Safety and sports glasses

Special lenses and frames incorporating eye protection are available for a variety of safety and recreational uses.

Anti-reflection coating eResearch by Navid Ajamin -- winter 2010

Spectacle lenses can be provided with anti-reflection coatings which virtually eliminate distracting reflections off the lens surfaces. Reducing reflected light is particularly helpful for computer users and for night driving. Anti-reflection coatings also improve the cosmetic appearance of your glasses and can make thick lenses look thinner.

Scratch-resistant / hard coating

Plastic lenses are lighter than traditional glass lenses but they scratch more easily. Scratched lenses can be irritating for the wearer and look unsightly. Scratch-resistant coatings are available to protect against damage and prolong lens life.

Multi-coated lenses

Multi-coated lenses uncorporate a combination of coatings - anti-reflection, scratch-resistant, water repellent and UV - to combine to improve the properies of your spectacles.

Reference: college-optometrists.org

CR-39, or allyl diglycol carbonate (ADC), is a plastic polymer commonly used in the manufacture of eyeglass lenses. It should not be confused with polycarbonate, a homopolymer made from bis-phenol A, a tough polymer widely used for glazing.

Material. CR-39 polymer is one of the trade names of the family poly allyl diglycol carbonate. The chemical composition of CR-39 is (C12H18O7)n, where H content is 6.6% wt, C content is 52.6% wt and O content is 40.8% wt.

Abbe's number is a measure of light dispersion. The dispersion coefficient or Abbe's number ranges from 20 for very “dense” flint glasses, over 65 for very “light” crown glasses, to 85 for fluorine crown glasses. Those glasses that have a higher Abbe number have a lower dispersion and vice versa.

What is the Abbe value of CR-39?

CR-39 plastic has an index of refraction of 1.498 and an Abbe number of 58.

CR-39 is a trade marked product of PPG Industries, originally developed by Columbia Chemical Co Inc which evolved through acquisition into the Chemical Division of PPG Industries. An alternative use includes a purified version that is used to measure neutron radiation, a type of ionizing radiation, in neutron dosimetry.

The CR stands for Columbia Resin. During WWII uncured CR-39 Resin was used to coat aircraft fuel tanks. The CR-39 would "self heal" the tanks when struck by flak. The trade name for the original and most popular plastic material used for eyeglass lenses. The abbreviation stands for “Columbia Resin #39,” because it was the 39th formula of a thermosetting plastic developed by the Columbia Resins project of PPG Industries back in 1940.

World War II or the Second World War (1 September 1939 – 2 September 1945) was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising their resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were put on trial for war crimes...

CR-39 is a material that was derived for the military as durable light weight plastic used on military planes in WWII. CR-39 plastic is actually ADC (Allyl Diglycol Carbonate), invented by an Ohio based company named Columbia Southern Chemical Company (CSCC) a subsidiary of Pittsburg Plate Glass Company (PPGC).

The first commercial use of CR-39 monomer was to help create lighter, more durable fuel tanks for the B-17 bomber aircraft in World War II. After the War, the Armorlite Lens Company in California is credited with manufacturing the first CR-39 eyeglass lenses in 1947. CR-39 plastic has an index of refraction of 1.498 and an Abbe number of 58.

Applications

CR-39 is transparent in visible spectrum and is almost completely opaque in the ultraviolet range. It has high abrasion resistance, in fact the highest abrasion/scratch resistance of any uncoated optical plastic. CR-39 is about half the weight of glass with an index of refraction only slightly lower than that of crown glass, and its high Abbe number yields low chromatic aberration, altogether making it an advantageous material for eyeglasses and sunglasses. A wide range of colors can be achieved by dyeing of the surface or the bulk of the material. CR-39 is also resistant to most of solvents and other chemicals, to gamma radiation, to aging, and to material fatigue. It can withstand the small hot sparks from welding, something glass cannot do. It can be used continuously in temperatures up to 100 °C and up to one hour in 130 °C.

In the radiation detection application, raw CR-39 material is exposed to proton recoils caused by incident neutrons. The proton recoils cause ion tracks, which are enlarged by an etching process in a caustic solution of sodium hydroxide. The enlarged ion tracks are counted under a microscope (commonly 200x), and the number of ion tracks is proportional to the amount of incident neutron radiation.

What is the difference between resin lenses and glass lenses？

In terms of characteristics:
The hardness of glass lens is very strong, and it can be heated to more than 300 degrees when scrubbing, while for resin lens, it can only be heated to about 80 degrees, so glass lens has strong heat resistance performance. However, the glass lens is easy to break and the weight is relatively heavy, while the resin lens is different. However, because the resin lens does not have super heat resistance, the lens is relatively soft and is easily scratched by foreign objects.

Does CR-39 block UV?

Conclusions: These data suggest that UV tinted CR-39 lenses provide protection against UV radiation that meets the ANSI Z80. 3-1996 Standard for non-prescription sunglasses and fashion eyewear.

What is a disadvantage of CR-39 lenses? Standard Plastic CR-39 Lenses

Some disadvantages of this material are that it scratches easy, does not provide adequate UV protection, is not as impact resistant as other lenses and is also heavier and thicker than the higher index plastics.

Functionally:
Resin lenses have the function of 100% UV protection from the sun, preventing the eyes from being damaged by various harmful rays, while glass lenses do not have the function of UV protection, and the optical transmittance of resin lenses is more than 2% higher than that of glass lenses. However, for patients with high myopia, resin lenses are thicker, so they will not be so beautiful to wear.
Although today's resin lenses have been greatly improved, they are much thicker than glass lenses. Therefore, in terms of high temperature resistance, glass lenses have a significantly better lifespan.

What is the difference between resin lenses and glass lenses? Both resin lenses and glass lenses have their own advantages, but I personally think that resin lenses are lighter in weight and less stress on the bridge of the nose than glass lenses. And the impact resistance is also relatively good, when it is impacted by the outside world, it will not be easily broken, which can protect the health and safety of eyes and vision to the greatest extent. Therefore, resin lenses are more suitable for children and myopia patients with relatively large diopter than glass lens optical lenses.

Common sense of lens material: -- eResearch by Navid Ajamin -- winter 2010
1. Material: PMMA: Acrylic (commonly known as plexiglass), which is cheap and heavy, and the phase clarity of the object is average. The lens is easily broken by external force.
PC: commonly known as space film Advantages: light lens (specific gravity is 1.20g/cm³), high strength, high impact resistance, not easy to split, better clarity than PMMA but inferior to CR-39, generally used for sports glasses and protective glasses; when the thickness of the material reaches When it is 2.5cm, it can be used as bulletproof glass; PC sheet can absorb (or block) almost all ultraviolet rays harmful to human eyes, which is especially suitable for drivers and computer operators.
Disadvantages: 1. It is easy to be scratched and the wear resistance reaches B. All PC sheets must be hard-coated to improve the surface hardness of the focusing lens.
2. The lens has a large chromatic aberration
PL (CABTAC): Commonly known as Poly Lay film, it is a mainstream product in the future market. It is light and effective against harmful light and reflected light. It can see objects with high definition and realism. The original film will not be broken but easily scratched. It is generally used for outdoor fishing. , and students wear all fishing goggles and student goggles in class.
CR-39: commonly known as high-grade resin sheet, it is a high-definition lens, expensive and light (specific gravity is 1.32g/cm³)
Advantages: strong impact resistance, high temperature resistance, 10 times higher than glass, so the lens is not easy to break, and the break is not sharp after breaking; the lens is light in weight; the absorption function of ultraviolet rays is better than that of ordinary optical glass sheets
Disadvantages: The sheet is easy to be scratched, and the requirements for the assembled frame aspherical mirror are high. The resin sheet should preferably be coated with an anti-reflection film to improve the light transmittance of the lens.
Older reading glasses should also be replaced regularly. Presbyopia is caused by the aging of the lens. With the increase of human age, the degree of aging of the lens will increase, and the required correction of the lens power must increase accordingly to meet the needs of the elderly in daily life.

There is no unified regulation on the specific replacement time. When the elderly wear glasses to read newspapers and feel tired and their eyes are sore and uncomfortable, they should be replaced.

There are many lens materials on the market today. Resin lenses are light and easy to carry, but they are easily scratched, so pay special attention to lens care. Glass lenses are cheap, but fragile, and if they are broken, they may cause extremely serious damage to the eyeballs, so they are not suitable for teenagers who exercise a lot.

What are OSHA approved safety glasses?

For safety glasses to be considered OSHA-approved, they must comply with the American National Standards Institute (ANSI) Z87. 1 standard. This standard outlines the requirements for impact resistance, coverage, and durability

Polycarbonate (PC)

• Organic material with very high breaking strength
• Inherently soft allowing it to absorb impacts, ideal for safety eyewear
• Mechanical strength class "F" (45 m/sec)
• About 20-25% thinner than plastic or glass lenses
• Requires scratch-resistant coating for durability
• Only limited resistance to chemicals and therefore not suited in combination with frameless safety spectacles

CR39 (Plastic)

• Lightweight organic material
• Very good optical performance even for high prescriptions
• Suitable for working with chemicals and paints / varnishes
• Mechanical strength class "S" (falling ball test)
• Good scratch resistance due to hard layer (optional)
• The middle of the lens should always be thicker in order to meet the requirements for tensile strength

Reference:

• en.wikipedia.org/wiki/CR-39
• uvex-safety.co.uk/en/cr39-versus-polycarbonate-lenses
• sciencedirect.com/science/article/pii/S1687850714000491
• worldoptic.com/lenses/standard-plastic-cr-39-glasses.php
• caglasses.com/blog/how-do-i-know-if-my-safety-glasses-osha-approved-or-not
• edlensxs.com/blogs/industry-news/what-is-the-difference-between-resin-lenses-and-glass-lenses

See Also:

• ophthalmic Lens material and design
• eyewear - Comparing Polycarbonate Lenses With Standard CR39 Lenses

Anti-Reflection Coatings

AR coatings are similar to the coatings found on microscopes and camera lenses. They consist of several layers of metal oxides applied to the front and back lens surfaces. Because of the layering effect, AR coatings sometimes have a hint of green or purple color, depending on the individual manufacturer's formula.

The most important benefits of anti-reflective (AR) coating may be the unseen advantage--relief from fatigue and eyestrain caused by glare. AR does have a big cosmetic advantage, but removing the distracting reflections and ghost images that contribute to eyestrain clearly is a bigger benefit. This increases comfort. Being more comfortable in anything we do is a benefit, especially wearing glasses. People always remark how uncomfortable glasses are. Well now you can offer a real solution to that problem. AR Coating!!

Nighttime driving is also enhanced with AR coatings by eliminating the reflections from street lights, headlights from on-coming vehicles, and taillights. By applying an AR coating more light can pass through the lens providing greater image contrast and clearer vision.

Beyond these benefits and features, other ideal candidates are:

1. High Index Wearers-AR helps reduce the concentric rings these strong prescriptions produce.

2. Low Vision Patients-The increase of light transmission from AR coatings can benefit low vision patients.

3. Light-sensitive patients

4. Sunglass wearers

5. First time wearers of glasses

6. Professionals

7. VDT users can benefit from AR's ability to reduce glare.

You get more out of life when you can enjoy it longer. Vision problems such as glare, reflections, ghost images and the fatigue they create reduces your enjoyment. AR coatings improve vision, reduce fatigue, and help you to enjoy every minute of life at work or at play.

AR coatings enhance appearance. It makes lenses look thinner by reducing distracting reflections. Also the wearers eyes are more visible and this improves eye contact for better communication.

Now, we have mention the cosmetic and comfort features but there are more than that. AR lenses when worn in daylight and indoors, most people find it provides noticeable better visual performance, making objects appear crisper and brighter. When reading a newspaper, magazine, or even a computer screen with AR coated lenses images and letters will appear sharper and crisper. [1]

Anti-reflective eye glasses are designed to reduce glare on the lenses. This serves the dual purpose of improving the wearer’s vision and enhancing the appearance of the glasses themselves, particularly in photographs taken with a flash. eResearch by Navid Ajamin -- spring 2008

Composition

1. Anti-reflective coating consists of a series of layers of metal oxides. In the 1980s and 1990s, when anti-reflective lenses were relatively new, the coating was only a single layer that could easily become scratched or smudged.

Today, multiple layers enhance the properties of the anti-reflective coating, including oil-resistant, water-resistant, static-resistant and protective scratch-resistant layers.

Process

2. The process used to apply anti-reflective coating varies depending on the manufacturer. In some cases the coating is sprayed on in liquid form, then exposed to high heat so that the liquid solution hardens and adheres to the lens.

Another process coats each lens with a liquid and places it inside a vacuum chamber, where the vacuum process hardens the coating. In yet another process the anti-reflective coating is built into the material and distributed throughout.Care

3. Anti-reflective lenses require a little more care than regular lenses. They should not be cleaned with harsh chemicals, which can damage the anti-reflective coating. Additionally, they should be cleaned or rubbed only with a wet cloth, as a dry cloth can scratch the lens.[2]

Benefits of anti-reflective coating

Anti-reflective coating (also called “AR coating” or “anti-glare coating”) improves vision, reduces digital eye strain and makes your eyeglasses look more attractive. These benefits are due to the ability of AR coating to virtually eliminate reflections from the front and back surfaces of your eyeglass lenses.

With reflections gone, more light passes through your lenses to optimize visual acuity with fewer distractions (especially at night), and the lenses look nearly invisible — which enhances your appearance by drawing more attention to your eyes and helping you make better eye contact with others.

AR coating is especially beneficial when used on high-index lenses, which reflect more light than regular plastic lenses. Generally, the higher the index of refraction of the lens material, the more light that will be reflected from the surface of the lenses.

For example, regular plastic lenses reflect roughly 8% of light hitting the lenses, so only 92% of available light enters the eye for vision.

Photolithography

Antireflective coatings (ARC) are often used in microelectronic photolithography to help reduce image distortions associated with reflections off the surface of the substrate. Different types of antireflective coatings are applied either before (Bottom ARC, or BARC) or after the photoresist, and help reduce standing waves, thin-film interference, and specular reflections.

High index plastic lenses can reflect up to 50% more light than regular plastic lenses, so even less light is available to the eye for vision. This can be particularly troublesome in low-light conditions, such as when driving at night.

Today’s modern anti-reflective coatings can virtually eliminate the reflection of light from eyeglass lenses, allowing 99.5% of available light to pass through the lenses and enter the eye for good vision.

By eliminating reflections, AR coating also makes your eyeglass lenses look nearly invisible so people can see your eyes and facial expressions more clearly. Anti-reflective glasses also are more attractive, so you can look your best in all lighting conditions.

The visual benefits of lenses with anti-reflective coating include sharper vision with less glare when driving at night and greater comfort during prolonged computer use (compared with wearing eyeglass lenses without AR coating).

When applied to photochromic lenses, AR coating enhances the clarity and comfort of these premium lenses in all light conditions without reducing their sun-reactive performance.

Anti-reflective coating also is a good idea for sunglasses. It eliminates glare from sunlight reflecting into your eyes from the back surface of tinted lenses when the sun is behind you. (Generally, AR coating is applied only to the back surface of sunglass lenses because there are no cosmetic or visual benefits to eliminating reflections from the front surface of dark-tinted lenses.)

Most premium AR lenses include a surface treatment that seals the anti-reflective layers and makes the lenses easier to clean. These hydrophobic surface treatments also repel water, preventing the formation of water spots on your lenses.

Some anti-reflective lenses have surface treatments that are both hydrophobic and oleophobic (also called lipophobic), which means they repel both water and oil. These combination treatments typically contain fluorinated materials that give the lenses properties that are very similar to those of nonstick cookware.

Is anti-reflective the same as anti-glare?

Anti-reflective vs Anti Glare

In short: anti glare coatings will protect against external light sources entering the glasses, while anti-reflective coatings will protect against both internal and external light.

Anti Glare

To get into the physics of it, anti glare solutions equip glasses with diffusive properties which diffuse light that would usually be reflected off of the surface of your lens. This means that instead of producing specular reflection, it creates a diffuse reflection. Instead of the light ray reflecting directly off the lens, it is broken up into many weaker rays, meaning the reflection is far weaker or, often, unnoticeable. This means that anti glare coatings significantly reduce the amount of light that is reflected off the surface of the lens.

Anti-Reflective

On the other hand, anti-reflective lenses go a step further. These solutions use diffusive properties to diffuse both external and internal light. While “internal light” might sound strange, it refers to the small number of transitional light waves which are let loose as the light goes from one medium (in this case, air) into another (the lens). If unchecked, these small light rays can reflect within the lens itself, causing strange visual artefacts that lead to eye strain and discomfort. While these internal reflections may still be present in glasses with anti glare coatings, anti-reflective lenses go the extra mile to ensure the best user experience possible.

Anti-reflective coatings are often used in camera lenses, giving lens elements distinctive colors. Such colors indicate the wavelength of visible light least affected by the antireflective properties of the coating. A variety of colors can be produced whose precise hue depends entirely on the thickness of the coating.

Reference:

1. robertsonoptical.com
2. milenyumtasarim.com
3. en.wikipedia.org/wiki/Anti-reflective_coating
4. allaboutvision.com/lenses/anti-reflective.htm
5. rx-able.com/blogs/blogs/is-anti-reflective-the-same-as-anti-glare

See also:

• Disadvantages of Anti-Glare Coating

• My glasses have an anti-reflective coating. How does that work?