Eyeglasses | Optical Center SmartBuyGlasses USA

What's My Lens Index?

Lens index tells how thick or thin your lenses would be. It is measured by numbers and it works an inverse manner - the higher the lens index is, the thinner the lens would be. People with higher prescriptions will need higher index lenses. 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.


What are high-index lenses?

High index lenses are thin, light and powerful lenses. Eyeglasses equipped with high index lenses are noticeable 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. 


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 choosing 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. 


1.5 index - Basic lens

Lenses with this lens index are conventional single vision lenses which are included in all eyeglass frames at SmartBuyGlasses. However, these are ideal only for people with a light prescription and for general purposes. Since they are thicker, they are heavier.

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


1.57 Index - Thin lens 

These lenses are thinner and lighter. They are recommended for people with SPH corrections between +/-5.00 and +/-4.00 and CYL corrections of +/- 3.00 and below.

Usually, they are 15% thinner than the 1.5 indexes.


1.59 Index - Polycarbonate lens 

Lenses with this lens index are the most recommended by the ophthalmologist. These are polycarbonate lenses, which are 10 times more impact-resistant than plastic and glass lenses. Also, these offer 100% UV protection.

These are best for rimless frames, for children, and people with an active lifestyle.


1.6 Index - Super thin lens 

Called “super thin”, these lenses are 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.


1.7 Index - Ultra thin 

Called “ultra-thin,” this type of lenses are 30% thinner than the standards. Lenses with this high lens index are recommended for people with strong vision need with SPH corrections around +/-7.00 and +/-9.00, and CYL corrections around +/-3.25 and +/-4.00.


1.74 Index - As thin as possible lens 

Called “as thin as possible,” these lenses 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.

Costly and availability are among the high index lens disadvantages.

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