What are high-index lenses?

What are high index lenses?

A high index lens is a type of eyeglass lens that bends (refracts) light more efficiently than ordinary glass or plastic lenses. This is because the lens material has a higher refractive index than ordinary glass or plastic lenses. A lens material with a higher refractive index produces thinner glass.

Therefore, if you want a thin and good-looking pair of glasses, choose lenses with a high refractive index. In general, the higher the refractive index of the lens, the thinner the glasses will be.

High-index lenses are especially useful if you have high levels of nearsightedness, farsightedness or astigmatism. If you have a high prescription, high index lenses can have a dramatic effect in thinning thick eyeglass lenses.

Refractive index range of lenses

The refractive index of eyeglass lenses ranges from about 1.50 to 1.80. Lens materials with a refractive index below this range will make your glasses thicker. Lens materials with a refractive index above this range will make your glasses thinner. The more nearsighted or farsighted you are, the more noticeable the difference will be.

Lens materials with refractive indexes higher than the standard CR39 plastic (1.50) and ordinary glass (1.52) are considered high index lenses. However, some high index lenses are much thinner than others.


The difference a high index lens material can make: normal plastic lenses (left) and high index lenses (right) have the same corrective effect on myopia. Image: Essilor

Below is a list of the most common lens materials used for eyeglasses. These materials are listed in order of refractive index from low (thick lenses) to high (thin lenses):

CR39 (standard) plastic - 1.50

Coronet (standard) glass - 1.52

Trivex - 1.53

Medium refractive index plastics - 1.54 to 1.56

Polycarbonate - 1.59

1.60 High Refractive Index Plastics - 1.60

1.67 High Refractive Index Plastics - 1.67

1.74 High index plastic - 1.74

How thin are high index lenses?

How much a high index lens will thin your eyeglasses depends on several factors:

Your lens prescription

The lens index

The design of the lens

The size and shape of the frame

You cannot change your lens prescription - a lens prescription is a lens prescription. (Unless you choose a vision correction procedure such as LASIK.)

But you can make choices based on the other factors mentioned above to make your glasses as thin as possible. To create the thinnest, most aesthetically pleasing glasses:

Choose a lens material with a refractive index greater than 1.60. The higher the refractive index, the thinner the lens. Lenses with an index of refraction of 1.67 and above may be less than half the thickness of ordinary plastic lenses. On the other hand, polycarbonate lenses (1.59 refractive index) may be only 20% thinner than regular plastic lenses.

Choose a high index lens with an aspheric design. Aspheric lenses are made with flatter curves and have a significantly thinner profile than regular plastic lenses.

Choose smaller frames. The smaller the frame, the thinner the high index lens. Also, make sure the pupil is as close to the center of the frame's lens opening as possible. This will also reduce the thickness of the lens.

How much lighter are high index lenses?

The weight of a high index lens depends on the factor of the specific gravity of the lens material. Basically, this is a measure of the density of the material.

Some high index lenses may be thinner than others (because they have a higher refractive index), but they may be heavier than thicker lenses (if they are made of a material with a much higher specific gravity).

In general, if you want glasses that are as light as possible, choose a lens material with a high refractive index and low specific gravity. The following are good choices:

1.67 High-index plastic lenses

1.71 High index plastic lenses

1.74 High index plastic lenses

These lenses are less than half the weight of regular glass lenses and 25 to 30 percent lighter than regular plastic lenses.

Trivex has the lowest specific gravity of any popular eyeglass lens material. This makes Trivex lenses extremely lightweight and comfortable. While Trivex lenses (refractive index of 1.53) may only be 10% thinner than regular plastic lenses, they can weigh up to 30% less.

Cost of High Index Lenses

In general, the higher the refractive index of a lens material, the higher the cost.

It is not uncommon for 1.67 Hi-Refractive Index lenses and 1.74 Hi-Refractive Index lenses to cost 3 to 4 times as much as standard plastic or glass lenses.

Please consult with a professional optometrist to discuss your specific needs and which type of high index lenses will fit your budget.

AR Coatings: A Must for High Index Lenses

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

Traditional glass or plastic lenses reflect about 8% of the light that would otherwise reach the eye. High index lenses reflect up to 50% more light than ordinary glass or plastic lenses.

Because of their high reflectivity, high index lenses must be coated with anti-reflective lenses (AR coating). AR coated high index lenses transmit up to 99.5% of the light to the eye for optimal vision.

And because AR coating virtually eliminates reflections from the lens, high index lenses are virtually invisible. Others see your eyes, not distracting reflections from the lens.

In addition, AR-coated high-index lenses give you clearer night vision than uncoated lenses - a real advantage for nighttime drivers.

Thanks for reading.
010@mikeeyewear.com
Cherish Chen