What's My Lens Index? Meaning & Comparison

Lens Index Meaning

Lens index tells how thick or thin your lenses would be. Also known as the index of refraction or refractive index, it is measured by numbers and describes how efficiently a material bends light. Refractive Index is what determines the ability of eyeglasses lenses to bend light. This is the ratio of the speed of light when it passes through the air to the speed of light when it passes through the lens material. 

Lens index works inversely. When the index number is high, we can infer that light travels more slowly through the lens material and light rays are bent more. As a result, higher index lenses correct the same amount of refractive error as lower index ones with less material, making high index lenses thinner and lighter than their conventional glass or plastic counterparts.

It works inversely - the higher the lens index is, the thinner the lens would be. Higher index lenses would be better suited for people with higher prescriptions. Knowing your index will determine the best lenses for glasses. Before we go through the lens index chart, let us first go through the following terms and abbreviations you may need to know:

  • SPH: means Sphere, a term used to indicate lens power to correct myopia (nearsightedness) or hyperopia (farsightedness). If you see a minus sign (-) before the sphere number, you are nearsighted, so you will have difficulty seeing distant objects clearly. If you see a plus sign (+), you are farsighted, meaning that objects nearby may be blurry.
  • CYL: means Cylinder, a term used to indicate lens power for astigmatism.

Types of Refractive Errors

A refractive error occurs when the shape of your eye does not correctly bend light. This results in blurred vision. The main types of refractive errors are myopia (nearsightedness), hyperopia (farsightedness), presbyopia (gradual loss of eye's ability to focus on nearby objects), and astigmatismEyeglass lenses are prescribed to correct such refractive errors with the necessary lens power (the degree to which light bends through the lens). Severe refractive errors require correction with high prescription lenses. Such strong prescriptions may mean thick and chunky plastic lenses. 

But with the emergence of high-index materials, the optical industry has been transformed. Now, refractive errors can be corrected with thinner lenses, with no compromise on efficacy. Thanks to high index lenses, high prescription glasses can now be sported in stylish, semi-rimless and even rimless styles. 

What is a high-index lens?

High index lenses are thin, light, and powerful lenses. Eyeglasses equipped with high index lenses are noticeably slimmer, more lightweight, and more stylish. That's why high index lenses are recommended for people with strong eyeglasses prescription. Typically, those with higher vision correction needs will be forced to wear thicker and bulky conventional glass or plastic lenses that are thicker towards the edges. Most high index lenses are also aspheric, making them slimmer and eliminating the “bug-eye” look to a great extent.

Lightweight lenses are even more of a benefit for farsighted 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 "bug-eye" look that conventional lenses cause in strong farsighted prescriptions.

What is the difference between high-index and low-index lenses?

Usually, most prescriptions are compatible with more than one specific lens index. However, being aware of the advantages and disadvantages of various lens indexes will help you choose the lenses best suitable for your glasses as well as for your lifestyle. Although thicker lenses (low index) are more affordable, they are available only for lower vision correction needs and do not bend light efficiently. By contrast, thinner eyeglasses lenses (high index) can accommodate many kinds of vision prescription needs and even reflect light properly, offering you better clarity of vision. 

Choose the best lenses for your prescription with the lens index chart below to know the thickness of lenses you should select for your new eyeglasses.

Lens Index Comparison

1.5 index - Basic lens

Lenses with this lens index are conventional single vision lenses which are included in all eyeglass frames at EyeglassesClub. However, these are ideal only for people with a light prescription and for general purposes. Since they are thicker, they are heavier. Arise Collective Clarity HD lenses provide advanced UV 400 protection, are highly water-resistant, aspheric and impact resistant. Learn more about the features of the Arise Collective Clarity Collection here.

These are recommended for Plano lenses with no visual correcting power and SPH prescription of approximately +/- 2.25 and below or a CYL correction of +/- 1.50 and below.

1.61 Index - Thin lens 

Called “super-thin”, these lenses are up to 25% thinner than the standard lenses. They are a stylish and great option for people with strong prescriptions around SPH +/-4.25 and +/-6.75, and CYL corrections around +/-2.25 and +/-3.00. For superior performance, opt for the Arise Collective Clarity 4K lenses.

1.67 Index- Very Thin lenses

These lenses are thinner than 1.61 index lenses and help with eye distortion as a result of stronger prescriptions and hence are the best pick for those with an SPH correction between +/-7.00 and +/-9.00, and a CYL correction between +/-3.25 and +/-4.00. Enjoy the most breakthrough lens technologies, optimized visual acuity, and state-of-the-art protection with Arise Collective Clarity 8K lenses.

1.74 Index - Ultra Thin lenses

Called “as thin as possible,” high index lens 1.74 are best for prescriptions with SPH corrections around +/-9.25 and above, and CYL corrections around +/-4.25 and +/-6.00. They are 35% thinner than the standard lenses. Although they appear thin, they are at the same time strong and will include the features to correct vision problems. High price and limited availability are among high index lens disadvantages.

All lenses offered at EyeglassesClub are covered by 20/20 Enhanced Lens Insurance, a warranty based on the value of the frames you purchase with up to 5 years of coverage.

What Lens Index Should I Get?

Your lens index would depend on your prescription and lifestyle. While thicker lenses are more affordable and can accommodate low amounts of vision correction needs, thinner lenses are lightweight, sleek, and can accommodate every type of vision need. A middle-of-the-road option would be the Arise Collective Clarity 4K lens with an index 1.61.

At EyeglassesClub, we offer both, traditional and digital eyeglass lenses. Digitally surfaced lenses are produced based on the patient's prescription with computer-controlled surfacing equipment- which is a lot more precise than traditional tools. Traditional fabrication techniques can surface lenses in power increments of 0.125 to 0.25 diopters, compared to 0.01 diopters that digital technologies can achieve. As a result, digitally fabricated lenses such as the Arise Collective Clarity Collection provide the widest fields of vision, sharper quality of images, better peripheral vision, and improve your ability to distinguish the most subtle differences in light versus dark.

Another point to consider is your pupillary distance. The improper pupillary distance can lead to blurry vision, double vision images, headaches, nausea, and even fatigue. With strong prescriptions, even the slightest error in pupillary distance measurement can cause frequent headaches. Use our Lens Scanner app, our FDA listed application to measure your pupillary distance accurately for free!

Most of the advanced designs and features are available in high-index lens materials. However, it's still best to ask your eye doctor so your vision problems are attended to.