What are high index lenses?

"High-index lenses are a type of eyeglass lens that has a high index of refraction. This means they can bend light more efficiently than other standard lenses. These lens materials are thinner, lighter, and less noticeable, and are used by people with strong prescriptions."

 

Spectacle lenses not only depend on the dioptric strength, which also depends on the refractive index.

Refractive index is a number of a lens material that indicates how efficiently light is reflected and quickly travels through the material. 

When light enters any type of spectacle lens, it slows down and bends at an angle within the lens material. This effect is known as refraction. The more efficiently the light is bent, the higher the index of refraction.

Low index lenses are less refractive. Light is only slightly bent, thus taking longer to pass through. For strong prescriptions, your lenses should be thicker to sufficiently refract the light to achieve the same level of vision correction. This can lead to bulkier and heavier lenses.

The working of both lenses is similar, but high-index lenses can bend light more efficiently. They can achieve the same level of correction with less material. That’s why they are significantly thinner and lighter.

As a rule of thumb, lenses with a refractive index of 1.50 or more are considered as “high index.” There are various refractive indexes of lenses available however they generally follow the same pattern of increments as listed further below.

 

What are the different indexes of lenses?

High-index lenses are considered above a refractive index of 1.50 and go up to 1.74.

• 1.50 = standard index
• 1.60 = thinned
• 1.67 = super thin
• 1.74 = ultra thinned

A lens with a refractive index of 1.74 could be up to 50% thinner than a standard index (1.50) lens.

Should I upgrade to high index lenses?

Upgrading to high index lenses depends on your individual needs and preferences. If you have a strong prescription and are looking for thinner and lighter lenses, then high index lenses may be a great option for you. They can also provide better aesthetics as they reduce the overall weight and bulk of your frame.

Additionally, high index lenses are a good option for those who have a higher prescription and need strong vision correction. Thick lenses can cause distortion in peripheral vision due to the magnification effect. High index lenses can help minimize this issue by reducing the thickness of the lens.

However, if you have a low or moderate prescription, upgrading to high index lenses may not be necessary as they will only provide minimal benefits in terms of weight and aesthetics. Too often do people pay for an index of lens with a marginally thinner or lighter profile.

 

How do I know if I need high index glasses?

If you have a strong prescription above ±3.00 diopters or a cylinder power above +/- 2.00, then high-index lenses is a good option for you. They'll be thinner, lighter weight and sleeker looking than standard index lenses.

To make things easier, I’ve created a simple table below to help you understand which lens index is most suitable for your prescription. The table is to be used as a general guideline which can help you avoid having unnecessarily thick “milk bottle” lenses. Equally, this advice can prevent you from paying for lens thinning when it isn’t really required for your prescription.

Recommended Lens Index Based on Prescription

 

Approx lens thickness chart

	Index	1.5	1.60	1.67	1.74
Dioptre
+6.00	Approx. thickness	8.3 mm	7.1 mm	6.4 mm	5.1 mm
+4.00	Approx. thickness	5.7 mm	5 mm	4.3 mm	3.6 mm
+2.00	Approx. thickness	3.3 mm	2.9 mm	2.8 mm	2.6 mm
-2.00	Approx. thickness	4.8 mm	3.6 mm	3.3 mm	2.9 mm
-4.00	Approx. thickness	7.6 mm	5.9 mm	5.3 mm	4.2 mm
-6.00	Approx. thickness	10.3 mm	7.9 mm	7.3 mm	5.9 mm
-10.00	Approx. thickness	16.9 mm	13.4 mm	12 mm	9.7 mm

 

High index lenses can also be made in what's called Aspheric design, meaning the lens has been made to a flatter profile than a Spheric equivalent. This further prevents the lenses from being overly thick, with the benefit of reduced peripheral distortion.

 

What are the advantages of high-index lenses?

#1 No 'bug eyes' for you

High-index lenses have less of a 'magnifying effect' on your eyes. This is purely aesthetic, but prevents your eyes from looking larger than they actually are.

 

#2 Slimmer lenses

High-index lenses are more efficient at letting light pass through, so they can be made thinner compared to standard index lenses. If you have a particularly strong minus Sphere, (-) a high refractive index will help to prevent the edges of your lenses from protruding from your frame.

 

#3 Lighter frame

High-index lenses are also lighter weight which can make your glasses frame more comfortable to wear. We’re only talking a few grams here, but it can really help to reduce their pressure on your face and hopefully stop them from slipping down your nose.

 

#4 Flatter & prettier

High index lenses can also be made in what's called as Aspheric design, meaning the lens has been made to a flatter profile than a Spheric equivalent. This further prevents the lenses from being overly thick with the benefit of reduced peripheral distortion.

 

 

What are the disadvantages of high index lenses?

#1 Higher cost

The main disadvantage of high index lenses is their higher cost compared to standard index lenses. Due to the more advanced technology and raw materials used, these lenses tend to be more expensive. Furthermore, these lenses have a higher demand due to their aesthetic appeal therefore a higher price can be charged. As a rule of thumb, the higher the index of the lenses, the higher the cost.

 

#2 Increased reflection

Despite their advantageous refraction, high index lenses are prone to being more reflective than standard index equivalents. For you, anti-glare coating is crucial to avoid any distracting/annoying reflections across your lenses, especially at night. This upgrade improves your visual acuity as more light can pass through your lenses. This coating also helps with eye contact, as people can see your eyes more clearly.

 

#3 Vision distortion

Resulting from a higher refractive index and thinner lens profile, high index lenses can cause more visual distortion - especially in your peripheral vision. In optics, this is known as aberration, or abbe for short and affects all optical lenses regardless of their refractive index.

To avoid this, accurate alignment of your pupil behind your lenses is important to reduce the chances of peripheral distortion through your lenses. This is achieved through proper centration by horizontally and vertically aligning your eyes behind the optical centre of each lenses.

When ordering glasses online, you can help to avoid unnecessary distortion by providing your pupillary distance and providing your ocular heights when ordering your lenses.

 

#4 More Brittle

High index lenses aren't as strong as standard index equivalents. Their lesser impact resistance makes them more brittle and susceptible to shattering. If you play contact sports or have a physically demanding occupation, you may prefer to choose high index lenses made from polycarbonate or Trivex, which offer greater durability and impact resistance.

 

Why are high-index lenses so expensive?

High index lenses are more expensive due to the materials and manufacturing processes involved, plus market forces such as their aesthetic appeal and subsequent demand. The higher refractive index substrate materials used in these lenses are more costly to produce, resulting in a higher price point for the end product.

Lastly, high index lenses are more desirable due to their aesthetic qualities, reduced bulk, and lighter weight. In turn, this attracts many glasses wearers who wish to have sleek, nice-looking glasses that don't magnify the look of their eyes. This demand raises the retail prices of high-index lenses as a higher price can be charged.

However, the benefits of high-index lenses make them worth the investment. They provide thinner and lighter lenses with superior optical clarity, making them a popular choice if you have a strong prescription.

 

High index lenses thickness chart

The difference in thickness between the various lens indexes depends on various factors such as your prescription, your pupillary distance and the size of your glasses frame. However, to get an idea of lens thickness per index, check out the handy chart below.

Is there a big difference between 1.67 and 1.74 high-index lenses?

The main difference between 1.67 and 1.74 high-index lenses is the thickness. On average, 1.74 lenses are about 10–16% thinner and lighter than 1.67 lenses. If your prescription has a Sphere of +/-9.00 or a Cyl of +/-4.00, then 1.74 index lenses are the best option to keep your lenses thinner, flatter, and lighter in weight.

 

Do high-index lenses make eyes look bigger?

Actually, High-index lenses do not create any visual distortion that makes eyes look unusually big or small. With this, your glasses look better and more natural on your face by reducing eye distortion. Whereas standard lenses can magnify the eyes due to their high thickness of the lens. This is especially beneficial if you have a stronger prescription, as thicker lenses can magnify and distort the size of the eyes. Better still, high index lenses with an Aspheric or even a Double Aspheric profile can reduce the side-effect of your eyes looking bigger or smaller.

 

Is 1.50 astigmatism high?

A dioptric Cylinder (Cyl) value of 1.50 on your prescription paper is generally considered as moderate astigmatism. Less than 1 is very mild, whereas above 2 indicates a strong degree of astigmatism. 

If your prescription indicates a Cyl value of 1.50, this means you have a slight deviation from a perfectly spherical curvature in your eye, which can cause images to appear stretched, blurry, or distorted. 

How much does it cost for high index lenses?

At Banton Frameworks, the cost of high-index lenses depends on the lens index, your prescription strength, and its coatings. To calculate the cost of your lenses, you can check out our handy lens calculator.
 

Key takeaways

• Index refers to refractive index
• The stronger the index, the better a lens can bend light
• 1.50 index lenses are considered 'standard index'
• 1.60 to 1.74 lenses are considered 'high index'
• The stronger your prescription, the higher the index you need
• The higher the index, the higher the cost
• High index lenses are thinner, lighter and flatter but also cost more and are more fragile than standard index equivalents
• Always invest in anti-glare coatings to reduce reflections for high index lenses
• Consider Polcarbonate or Trivex lens materials if you need high impact resistance

Hopefully you found this article helpful. Please check out our other eyecare blogs. Thanks for stopping by.