1.67 vs 1.74 High Index Lenses: Which Should You Choose?

For a strong prescription, choosing between 1.67 and 1.74 high index lenses usually comes down to one question: how much additional thickness reduction do you actually need?

Both are high-index materials. Both are designed to produce slimmer lenses than conventional lower-index plastic under comparable conditions. The difference is that 1.74 has a higher refractive index, so it can bend light more efficiently and can generally produce a thinner lens for the same prescription and frame.

That does not make 1.74 automatically better for everyone. Prescription strength, frame size, lens shape, optical design, finished weight, and cost all belong in the decision.

What Do 1.67 and 1.74 Mean?

The numbers refer to the refractive index of the lens material.

Refractive index describes how strongly a material bends light. When a lens material has a higher refractive index, less curvature or physical thickness is generally required to create the prescribed optical power.

This is why high-index lenses become increasingly useful as prescription strength rises.

For more background on refractive index, see our High Index Lenses Explained guide.

Is 1.74 Thinner Than 1.67?

Under comparable conditions, 1.74 can generally be made thinner than 1.67 for the same prescription.

The practical difference is usually more meaningful in stronger prescriptions. If the prescription is relatively moderate, changing from 1.67 to 1.74 may produce a smaller visible improvement than the index numbers suggest.

The finished lens thickness is also influenced by:

• sphere and cylinder power
• lens shape
• frame width and height
• pupillary distance
• decentration within the frame
• lens design
• minimum center or edge thickness required for the material and construction

So while 1.74 has greater thinning potential, the actual pair of glasses must be considered as a complete optical system.

When Does 1.67 Make Sense?

1.67 is a popular high-index choice because it offers substantial thickness control without automatically moving to the highest commonly available plastic index.

It is often worth considering when:

• a stronger prescription is making standard lenses look bulky
• you want a slimmer profile but do not necessarily need maximum thinning
• the selected frame is reasonably compact
• you want to balance thickness, appearance, and cost

For many strong prescriptions, 1.67 can already produce a significant cosmetic improvement compared with conventional plastic.

That is why it should not be viewed as a compromise simply because 1.74 exists.

When Does 1.74 Make Sense?

1.74 becomes most compelling when lens thickness is a major concern and the prescription is strong enough for the additional index to make a useful difference.

It may be worth considering when:

• the prescription is very strong
• edge thickness in a minus prescription is particularly noticeable
• center thickness in a strong plus prescription is a concern
• you want the greatest practical thickness reduction available among common plastic high-index options
• the chosen frame makes lens thickness difficult to conceal

The stronger the prescription, the more opportunity there is for the higher index to show a visible benefit.

Is 1.74 Always Lighter Than 1.67?

No.

Lens weight depends on both the volume of material and the density of that material.

A 1.74 lens may use less physical material because it can be thinner, but high-index materials do not all have the same density. The thinner lens is therefore not guaranteed to be lighter in every prescription and frame.

This is an important distinction because “thinner” and “lighter” are often used as though they mean exactly the same thing.

If weight is your main concern, the frame itself also matters. A smaller lens opening reduces the amount of lens material, while a lightweight frame can reduce the total weight of the finished glasses.

Does 1.74 Give Better Vision Than 1.67?

Not simply because the index number is higher.

The purpose of moving from 1.67 to 1.74 is primarily to gain additional refractive efficiency and thickness control. A higher index should not be treated as a quality score for vision.

Visual performance depends on the complete lens design, prescription accuracy, optical centration, fitting measurements, surface treatments, and individual sensitivity.

For this reason, choosing 1.74 for a prescription that does not benefit meaningfully from the extra index may add cost without giving the wearer an equally meaningful advantage.

What About Reflections and Anti-Reflective Treatment?

High-index materials have higher surface reflectance than conventional lower-index plastic. A good anti-reflective treatment is therefore particularly useful with high-index lenses.

Reducing surface reflections can improve the appearance of the lenses and allow more light to pass through rather than reflecting from the front and back surfaces.

This applies to both 1.67 and 1.74 lenses.

Frame Choice Can Matter as Much as Lens Index

If the goal is thinner high-prescription glasses, changing the frame can sometimes be just as important as changing the lens material.

For a strong minus prescription, a very large lens opening places the outer edge farther from the optical center, which can increase edge thickness. For stronger plus prescriptions, frame dimensions and required lens diameter can also affect center thickness.

A smaller, well-centered frame can therefore make a major difference.

This means that choosing a very large frame with 1.74 lenses is not automatically a better thickness strategy than choosing a well-proportioned frame with 1.67.

Our High Prescription Glasses Guide explains how frame size, PD, lens shape, and index work together.

1.67 vs 1.74 for Different Prescription Strengths

There is no universal prescription cutoff that works for every wearer because cylinder power, frame dimensions, lens design, and individual priorities can change the calculation.

A useful way to think about the decision is:

• Mild prescription: Neither 1.67 nor 1.74 may be necessary simply for thickness.
• Moderately strong prescription: 1.67 may already provide an effective balance of thickness control and value.
• Strong prescription: Compare 1.67 and 1.74 together with the selected frame.
• Very strong prescription: 1.74 becomes increasingly relevant when maximum practical thinning is a priority.

The exact recommendation should still be based on the actual prescription rather than a broad category alone.

Is the Extra Cost of 1.74 Worth It?

It can be when the stronger material index creates a visible improvement that matters to you.

If your prescription is very strong and lens thickness is one of your main concerns, paying more for 1.74 can be a sensible upgrade.

If your prescription is moderate, your frame is already compact, and 1.67 produces a clean result, paying for 1.74 simply because it has the highest number may provide limited practical value.

The best value comes from using the index where it solves a real problem.

How to Choose Between 1.67 and 1.74

Before deciding, consider these questions:

1. How strong is the prescription?
2. Is lens thickness currently a visible concern?
3. How large is the selected frame?
4. Where will the eyes sit within the lens openings?
5. Is maximum thinning important enough to justify the additional cost?

Those answers give a much better basis for choosing than simply assuming the highest index is always the premium option.

The Bottom Line

1.67 and 1.74 are both useful high-index lens materials for stronger prescriptions.

1.67 often provides a strong balance between thickness control and overall value. 1.74 provides greater thinning potential and becomes increasingly worthwhile as prescription strength and thickness concerns increase.

The smartest choice is the one that matches your actual prescription and frame—not simply the larger number.

If you are choosing glasses for a stronger prescription, browse our High Prescription Glasses → and consider the frame and lens index together.