High refractive index vs. regular lenses: What’s right for you?

hand holding a pair of spectacles

High-index spectacle lenses are the right choice if you want thinner, lighter lenses and glasses that are as attractive and comfortable as possible.

Thinner, lighter high-index lenses are especially recommended if you have a strong eyeglass prescription for short sightedness, long sightedness or astigmatism. But high-index lenses can make your spectacles noticeably slimmer, lighter and more attractive regardless of how strong your prescription is.

Most spectacle wearers are short sighted, which requires corrective lenses that are thin in the centre but thicker at the edge of the lens. The stronger the prescription, the thicker the edges.

Most of today’s fashionable frames are made of plastic or metal with rims thinner than the lens itself.

Also, popular rimless mountings mean that the edges of the lenses are completely exposed.

In either case, the lens edges are highly visible, and thicker edges can detract from the appearance of your eyewear.

How high-index lenses vs. regular spectacle lenses

Spectacle lenses correct refractive errors by bending (refracting) light as it passes through the lens. The amount of light-bending ability (lens power) that’s needed to provide good vision is indicated on the spectacle prescription provided by your optician.

The difference a high-index lens material can make: the same correction for nearsightedness in regular plastic lenses (left) vs. high-index lenses (right). Images: Essilor

 

Refractive errors and lens powers required to correct them are measured in units called dioptres (D). If you are mildly shortsighted, your lens prescription might say -2.00 D. If you are highly myopic, it might say -8.00 D.

If you are longsighted, you need “plus” (+) lenses, which are thicker in the centre and thinner at the edge.

Regular glass or plastic lenses for high amounts of shortsightedness or long sightedness can be quite thick and heavy.

Fortunately, manufacturers have created a variety of new “high-index” plastic lens materials that bend light more efficiently.

This means less material can be used in high-index lenses to correct the same amount of refractive error, which makes high-index plastic lenses both thinner and lighter than conventional glass or plastic lenses.

Advantages of high index-lenses
Thinner

Because of their ability to bend light more efficiently, high-index lenses for shortsightedness have thinner edges than lenses with the same prescription power that are made of conventional plastic material.

Lighter

Thinner edges require less lens material, which reduces the overall weight of the lenses. Lenses made of high-index plastic are lighter than the same lenses made in conventional plastic, so they’re more comfortable to wear.

High-index glass lenses also have thinner edges, but high-index glass is heavier than conventional glass, so there is not as much weight savings with glass as there is with plastic lenses.

Lightweight lenses are even more of a benefit for long sighted prescriptions, which can make conventional lenses very heavy.

And most high-index lenses also have an aspheric design, which gives them a slimmer, more attractive profile and reduces the magnified look that conventional lenses cause in strong longsighted prescriptions.

High-index lens choices

There is a wide variety of thin, lightweight high-index spectacle lenses, based on how efficiently they bend light.

The light-bending ability of spectacle lenses is determined by the “refractive index” of the lens material. This refractive index is the ratio of the speed of light when it travels through air to the speed of light when it passes through the lens material.

The speed of light is reduced the more it is refracted as it passes through a lens material. Therefore, lenses that bend light more efficiently have a higher refractive index than those that bend light less efficiently, and lenses with a higher refractive index are thinner than lenses of the same power made of materials of a lower refractive index.

In short: the higher the refractive index, the thinner the lens.

Conventional plastic lenses have a refractive index of approximately 1.50. For glass, it’s 1.52.

Any lens material with a refractive index that’s higher than that of glass or plastic is considered to be high-index.

High-index plastic lenses are now available in a wide variety of refractive indices, typically ranging from 1.53 to 1.74. Lenses with a refractive index of 1.70 or higher typically are at least 50 percent thinner than conventional plastic lenses.

Also, generally speaking, the higher the index, the higher the cost of the lenses.

Your spectacle prescription also determines what kind of high-index material you might want for your lens. The highest index materials are used primarily for the strongest prescriptions.

If you want high-index lenses, be sure to ask for them. But rely on your optician’s advice regarding which index to use. Your optician can explain which high-index lenses are the best choice for your needs and budget.

Most of today’s popular lens designs and features — including progressive lenses and photochromic lenses — are available in high-index materials. But there are exceptions, so ask us for details.

AR coating: A perfect companion for high-index lenses

All lens materials block some light from passing through the lens. This light reflects back from the lens surface, causing distractions and reducing the clarity of night vision.

Conventional glass or plastic lenses reflect about 8 percent of light that otherwise would reach the eye. High-index lenses reflect up to 50 percent more light than conventional glass or plastic lenses.

For the best vision and appearance, it’s a good idea to have an anti-reflective lens coating (AR coating) applied to high-index lenses. AR-coated high-index lenses transmit up to 99.5 percent of light to the eye for optimum vision.

And because AR coating virtually eliminates lens reflections, it makes high-index lenses appear nearly invisible, so others see your eyes, not your lenses.

Also, studies have shown that spectacle lenses with anti-reflective coatings provide sharper night vision with less glare — a real advantage for night drivers.

Source: all about vision – www.allaboutvision.com/en-gb/eyeglasses/high-index-lenses/


Wearing a face mask? Here are 6 ways to avoid foggy glasses

While face masks help us avoid unknowingly transmitting coronavirus, millions of eyeglass wearers are discovering the nuisance of mask-induced foggy lenses.

With the World Health Organization (WHO) now recommending the wearing of face masks to curb the spread of COVID-19, fogged-up glasses are a problem “affecting a large chunk of the population,” says Chicago optometrist Joanna Slusky, founder and CEO of Halsted Eye Boutique.

What can you do about your fogged-up glasses?

We have compiled seven tips for lifting the fog from your glasses when you’re wearing a mask, but first let’s go over why your lenses are fogging up in the first place.

Why are my glasses foggy?
Body heat and air flow lead to foggy lenses, explains optician Shannen Knight, owner of A Sight for Sport Eyes, an eyewear retailer based in West Linn, Oregon.

When you’re wearing a face mask, you repeatedly breathe out warm air. This air then can sneak out of the top of your mask and steam up the lenses of your glasses. Of course, this can make it difficult to see.

According to a study published in The Annals of The Royal College of Surgeons of England, a face mask directs much of the exhaled air upward.

The “misting” of lenses happens when warm water vapor from your breath lands on the cooler lenses, producing tiny droplets that scatter light and reduce the lenses’ ability to transmit contrast (when light colors remain light and dark colors remain dark).

“The droplets form because of the inherent surface tension between the water molecules,” the study’s authors said.

6 ways to avoid foggy glasses

Now that you know why your lenses fog up, let’s review seven ways to prevent this fog when you’re wearing glasses and a face mask.

  1.  Seal the mask

A common trick employed by doctors involves sticking a piece of double-sided tape across the bridge of the nose before putting on a mask, says Shaun Veran, co-founder of OURA. OURA’s wellness products include reusable, antibacterial face masks.

“If you place the double-sided tape between the inside of the mask and the bridge of your nose, it will create a better seal,” Veran says. “You can also place an additional piece of cellophane or masking tape over the mask as well.”

2. Make sure the mask fits well

A loose-fitting mask lets exhaled air head toward your glasses, but a snugly fitting mask can shoot that air out of the bottom or sides of the mask and away from your glasses.

For a better fit, Veran recommends looking for masks equipped with moldable pieces around the nose (such as a metal strip) or masks that come in various sizes.

“If the mask is well-fitted, it will dramatically help to prevent the amount of hot air that can reach the lenses,” Veran advises.

“Make sure that your face mask has a snug fit around the nose bridge,” he adds. “The more conformed the mask is around the bridge of your nose, the less of that hot air will end up hitting your lenses.”

If you’ve crafted your own cloth mask, create a seal around the nose by inserting a moldable item into the upper part of the mask, Slusky says. This could be a paper clip, pipe cleaner, twist tie or folded piece of aluminum foil.

Looking for more advice on how to properly wear your face mask? The CDC details how to make a face mask (and how to clean it afterward).

3. Adjust your glasses

If your glasses have nose pads, you can tweak the pads so that the frames sit slightly farther from your face, Knight says.

“This will allow that hot air to escape instead of getting trapped between your face and the lenses of the glasses,” she says.

Knight cautions that altering the nose pads may slightly change your vision if you wear glasses with progressive lenses or lenses with a strong prescription. If that happens, you might need to hold your head at a different angle to compensate for the vision change, she says.

4. Try de-fogging products

Applying over-the-counter anti-fogging sprays, waxes and gels to your lenses before putting on your glasses can quickly disperse tiny fog droplets when you’re wearing a mask, Knight says.

“Some work better with different body chemistry, so you may need to try a few brands to see which one works best for you,” she says.

She warns against using anti-fogging products designed for cars or other purposes, as they might ruin your prescription lenses.

Ask us about the anti-fog wipes we stock in practice.

5. Breathe downward

Well, it might be awkward, but breathing downward can be a quick ant-fog fix, Slusky says. This sends the air away from your glasses.

How do you breathe downward? Hold your upper lip over your lower lip. Then blow air downward, as if you’re playing a flute.

6. Check out anti-fog lenses

This won’t fix your foggy-lens problem right away, but you might consider buying lenses with an anti-fog coating. (such as Optifog lenses) An anti-fog coating gives you a hassle-free answer to foggy lenses, regardless of whether the obstructed vision is triggered by a face mask or something else.

orignal source:

allaboutvision.com/en-gb/coronavirus/avoid-foggy-glasses-face-mask/

article edited


Adidas Performance Eyewear

adidas Sport eyewear is now a complete optical supplier offering a new range of unique sports lenses made for adidas frames.

WHY PRESCRIPTION
Just a small change in prescription drastically increases your risk of losing focus. High quality sports eyewear protects the eyes and provides first class vision. For athletes who require prescription lenses, adidas eyewear offers a range of prescription solutions compatible with their individual needs and types of sport. You can choose between direct glazing, adapter, and clip-in solutions to ensure optimal performance through optimal vision – your individual prescription solution, built for performance!

adidas Sport eyewear uses Shamir’s Attitude III® sports design for both Single Vision and Progressive lenses (direct glazing/adapter solutions) with our unique LSTTM  technology.

LSTTM works like a color equalizer, enhancing the perception of pure primary colors.
This results in an improved color perception and high contrast vision.

Perfect for sports that takes you in and out of shaded areas.

KEY BENEFITS
• less eye stress and better vision for your sport
• constant, high contrast vision
• improved natural color perception
• enhancement of details and contours
• equal light harmonization
• reducing light to a comfortable level

Shamir Attitude III®  Progressive and Single Vision sports lenses support a wide range of panoramic angles and base curves to optimally suit the wrap angle of adidas Sport eyewear while mainting all of the design advantages.

LSTTM technology is only available in adidas Sport eyewear.

Our best selling collection evil eye halfrim pro is now available with our latest innovation, the Vario lens.

The new photochromic Vario lenses have the ability to automatically change
FROM A CRYSTAL CLEAR TO DARK TINT, featuring a transmission range from 14 to 89%. Utilizing our Injection Technology, the wafer inlay is injected directly into the lens. The vario wafer allows the vario lens to automatically adapt to natural lighting conditions (UV radiation), at a speed that rivals that of the best on the market. The adidas Sport eyewear Vario lens offers maximum longevity and durability thanks to the use of our ingenious Injection Technology.


Special Event- William Morris London and Nikon Lenswear style day.

We are very pleased to announce a special event taking place on WEDNESDAY 13TH SEPTEMBER.

William Morris Eyewear and Nikon Lenswear will be with us all day, to promote the latest frames and lenses available.

                                    

We will be offering discount on frames and lenses dispensed on the day, with refreshments and goodie bags too.

 

           

               

Our resident Optometrist, Kinni will be available for pre booked eye examinations, to ensure your prescription is up to date, before you select your new style.    

Please call in to have a look at the latest William Morris London and Black Label frames, and enjoy some tea and cake too!