What are high index lenses?

High index lenses are prescription lenses made from materials that bend light more efficiently than standard lens materials. Because they bend light more efficiently, the same prescription can often be made thinner and lighter.

The higher the index number, the thinner the lens can usually be. Common lens indexes include 1.50, 1.60, 1.67 and 1.74.

Why lens index matters

Lens index affects the thickness, weight and appearance of your lenses. For lower prescriptions, standard lenses can work perfectly well. For stronger prescriptions, choosing a higher index can make the lenses look neater in the frame and feel more comfortable on the face.

It is not about making your prescription stronger or weaker. Your vision correction stays the same. The index changes the lens material and how efficiently that material bends light.

What do 1.50, 1.60, 1.67 and 1.74 mean?

These numbers refer to the refractive index of the lens material. In simple terms, they describe how efficiently the lens bends light.

1.50 index lenses

1.50 is a standard lens index and is usually suitable for lower prescriptions. It is often a good value option where lens thickness is not a major concern.

1.60 index lenses

1.60 lenses are thinner and lighter than standard lenses. They are often a sensible upgrade for moderate prescriptions or for people who want a better balance of thickness, weight and value.

1.67 index lenses

1.67 lenses are noticeably thinner, especially at the edges of minus prescriptions. They are commonly chosen for medium to stronger prescriptions where appearance and comfort matter.

1.74 index lenses

1.74 lenses are usually the thinnest commonly available plastic lens option. They are best suited to stronger prescriptions where reducing thickness and weight is a priority.

Which lens index is right for you?

The right index depends on your prescription, frame size, frame shape and how you want the glasses to look and feel. A higher index is not always automatically better for everyone.

If your prescription is low, a standard lens may be perfectly fine. If your prescription is stronger, a higher index lens can make a much more noticeable difference.

When are high index lenses worth it?

High index lenses are usually worth considering if you have a stronger prescription, want thinner lens edges, prefer a lighter pair of glasses or are choosing a frame where lens thickness may be more noticeable.

They can be especially helpful with larger frames, full-rim frames, stronger minus prescriptions and prescriptions where cosmetic appearance is important.

High index lenses and frame choice

Frame choice makes a big difference to final lens thickness. Even the best high index lens can look thicker than expected if the frame is very large or the prescription is not well matched to the frame shape.

Smaller, rounder frames usually help reduce lens thickness. Very wide, oversized or angular frames can make lens edges more noticeable, especially with stronger minus prescriptions.

Minus prescriptions and edge thickness

If you are short-sighted, your lenses are usually thinner in the centre and thicker at the edges. This is where high index lenses can make a big difference, because they can reduce the edge thickness that shows around the frame.

Plus prescriptions and centre thickness

If you are long-sighted, your lenses are usually thicker in the centre. High index lenses may still help, but frame size, lens design and accurate fitting are especially important.

Are thinner lenses always better?

Not always. Higher index lenses can be thinner and lighter, but they also tend to cost more. In some prescriptions, the visible difference may be small, especially if the frame is already well chosen.

This is why it is better to choose lens index based on the whole order, not just the prescription numbers alone.

Do high index lenses include coatings?

High index lenses are usually best paired with a good anti-reflection coating. This helps reduce reflections and improves the appearance of the lenses in the frame.

At Burghley & Co, lens options are checked before your order is made so the prescription, frame and lens choice work together properly.

Common mistakes when choosing high index lenses

• Choosing 1.74 lenses when the prescription does not really need them.
• Picking an oversized frame and expecting the lenses to look very thin.
• Ignoring frame shape when trying to reduce lens thickness.
• Assuming higher index always means better vision.
• Choosing lenses based only on price rather than prescription and frame suitability.

Scott’s advice

High index lenses are genuinely useful, but they should be recommended properly. The aim is not always to sell the thinnest lens possible. The aim is to choose the lens that gives the best balance of appearance, comfort and value for your prescription.

For lower prescriptions, standard or 1.60 lenses may be more than enough. For stronger prescriptions, 1.67 or 1.74 can make a real cosmetic difference. Frame choice still matters, though. A well-chosen frame with the right lens index will almost always look better than an oversized frame with the most expensive lens.

Related guides

For more help, read our guides to choosing prescription lenses, choosing glasses frames, understanding your prescription, lens coatings and varifocal lenses.

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