What Is Lens Index and Which One Do You Need?

When choosing prescription glasses, selecting your frame is only part of the process.

You may also be given a choice of lens index, with options such as standard, 1.6 and 1.67.

At first glance, those numbers don't tell you very much. But lens index can make an important difference to the thickness and appearance of your finished glasses, particularly if you have a stronger prescription.

What does lens index mean?

Lens index refers to the refractive index of the lens material.

In simple terms, it describes how efficiently the material bends light.

A higher-index material can produce the required optical power using a different lens profile, which can allow stronger prescriptions to be made thinner than they would be in a standard lens material.

Does a higher index give you better vision?

Not simply because the number is higher.

A 1.67 lens isn't an upgrade because it gives everybody sharper vision than a standard lens.

The prescription provides the correction your eyes require.

The main reason for choosing a higher-index material is usually to help manage lens thickness in stronger prescriptions.

When are standard lenses suitable?

Standard lenses can be a perfectly sensible option for many low and moderate prescriptions.

If your prescription doesn't naturally produce particularly thick lenses, paying for a higher index may provide relatively little cosmetic benefit.

This is why the strongest or most expensive lens option isn't automatically the right choice for everybody.

What are 1.6 lenses?

A 1.6 lens is a higher-index option that can help reduce thickness compared with a standard lens material.

It can be a useful middle ground for prescriptions where lens thickness is beginning to become more noticeable.

The exact finished thickness will still depend on your prescription and the frame you choose.

What are 1.67 lenses?

A 1.67 lens uses an even higher-index material.

It's commonly considered for stronger prescriptions where reducing lens thickness is more of a priority.

Again, 1.67 doesn't make a strong prescription invisible. It can help reduce thickness, but the finished result is influenced by several other factors.

Your frame still matters

Choosing a higher-index lens doesn't mean you can ignore frame size and shape.

For stronger minus prescriptions, for example, a very large frame can result in more noticeable edge thickness.

Combining an appropriate frame with an appropriate lens index can therefore be more effective than concentrating on lens material alone.

Your prescription matters too

Two people choosing the same 1.67 lens material and the same frame could still receive glasses with very different-looking lenses.

That's because the prescription itself has a major influence on the finished result.

The right and left lenses can even differ in thickness if the prescription is stronger in one eye.

Is the highest index always best?

No.

It's better to choose an index appropriate for your prescription than automatically selecting the highest number available.

For a relatively low prescription, the difference in thickness may be small enough that a higher-index option offers limited practical benefit.

For a stronger prescription, the difference can become considerably more useful.

Think about the complete pair of glasses

Lens index is only one part of the finished product.

Your prescription, frame dimensions, frame shape, pupil position and lens material all work together to determine how your glasses ultimately look and feel.

Understanding what lens index actually means makes it easier to choose an option based on your prescription rather than assuming that a bigger number must always be better.