Five thin clear lenses of the same size stood on their edges in a row on a dark surface, each turned so both its face and its slim polished edge show, each edge a little slimmer than the one before, warm light running along every one.

Choosing your lens index

Index buys thinness, not clarity. Here is what each one is for — and why the lowest index that looks right is usually the correct answer.

Index reference

Two questions, kept apart. What an index supports is what the lens is made to do; what we'd recommend is what an optician would actually dispense. They are not always the same — at 1.50 especially — and separating them is the honest way to show it.

Index	What it supports	What we'd recommend
1.50Standard thickness	Up to 4.00 — default for clear prescriptions	Cap at 2.00; reach for 1.60 above, for cosmetics and thickness
1.56Thinner and lighter	Photochromic — made to order, or finished stock	—
1.60Thin · ideal for rimless · MR-8	4.00–6.00, or rimless and semi-rimless at any power	Recommended for moderate-to-high powers, for cosmetics and thickness
1.67High index · much thinner	6.00–8.00	—
1.74Ultra thin · strongest prescriptions	Above 8.00	—

Sphere power−4.00diopters of sphere

Estimated edge-thickness reduction

1.50
Standard referenceStandard 1.50 material
1.56
Up to 10% thinnerthan 1.50 at −4.00, indicative
1.60
Up to 20% thinnerthan 1.50 at −4.00, indicative
1.67
Up to 30% thinnerthan 1.50 at −4.00, indicative
1.74
Up to 40% thinnerthan 1.50 at −4.00, indicative

Dashed outline: the same power in 1.50Schematic shapes — not to scale, not a cross-section of a finished lens

Set your own sphere power and see how much thinner each index runs against standard 1.50, with the 1.50 profile dashed behind each shape. The percentages are indicative and the shapes are schematic — neither is a measurement of a finished lens. It answers how much thinner, not which to buy; the reference table above and your optician answer that.

Relative comparison · indicative percentages against 1.50, not measurements

Important

Visual simulation only. Actual finished-lens thickness may vary depending on prescription, cylinder and axis, lens design, lens blank and base curve, blank diameter, frame size and shape, PD and decentration, fitting position, minimum center or edge thickness, and laboratory processing.

What else changes with index

Index	Abbe	Surface reflection	In practice
1.50	58	4.0%	Standard thickness
1.56	—	4.8%	Thinner and lighter
1.60	41–42	5.3%	Thin · ideal for rimless · MR-8
1.67	31–32	6.3%	High index · much thinner
1.74	32–33	7.3%	Ultra thin · strongest prescriptions

Thinner is not automatically better, and it is not automatically lighter. A lower Abbe number means more color fringing at the edges of vision, which some wearers notice above roughly 3.00 diopters; and the denser high-index materials can weigh more than a thinner-sounding number suggests.

Materials and Abbe numbers are the material manufacturers' published figures, not CLIFF measurements.

1.50 — the standard

Every lens material is a compromise between three things: how thin it can be made, how much it weighs, and how cleanly it handles light. 1.50 is where that compromise is easiest — and that is why it remains the standard, not because it is basic.

Of every index in the range, 1.50 handles light the most cleanly. It has the least dispersion — colors stay together instead of separating faintly at the edges — which makes it, strictly speaking, the best optical material CLIFF offers. What it does not do is stay thin as power climbs. Up to around 4.00 diopters the edge thickness is unremarkable in most frames, and there is no reason to pay for anything else.

Choose 1.50 when: the prescription is mild, the frame has a rim, and you would rather spend the difference on a better design or coating — which changes what you see far more than a thinner edge does.

1.56 — the stock and photochromic index

1.56 has a particular place in the CLIFF range: it is the one index made both as ready-made stock and to order — and made to order, it comes photochromic only. Every photochromic lens starts here — the Photo-Z stock lens, the photochromic option on Dynamix, and the base of the range in Zenn and Zenn AI, which also make photochromic at 1.60, 1.67 and 1.74. It is the index of the ready-made Versatile line, which comes in a clear BLUESAFE version and a photochromic one (Versatile Photo-Z).

There is a reason photochromic standardizes here. Photochromic performance depends on the marriage of the light-reactive layer and the material beneath it, and standardizing on one proven base means every Photo-Z and photochromic option behaves the same way — same darkening, same fade-back, same even color — whatever design carries it. One material, tuned once, consistent everywhere.

You'll meet 1.56 when: you order any CLIFF photochromic lens, at any tier, or you choose the ready-made Versatile — the fastest, most affordable way into a CLIFF progressive.

1.60 — the tough one

1.60 is made of MR-8, and MR-8 is the reason this index has a different reputation from every other: it is tough. Tough enough that CLIFF backs it with a twelve-month breakage warranty — the only index in the range that carries one.

That toughness is not an abstract comfort. In a rimless or semi-rimless frame the lens is drilled, and the mounting screws bear directly on the material. A brittle lens fails at exactly those holes. MR-8 doesn't, which is why 1.60 is the professional's default answer for rimless work, and why it earns its place even at prescriptions where thinness alone wouldn't demand it.

It is also usefully thinner and lighter than 1.50 — the sensible step up for moderate prescriptions from about 4.00 to 6.00.

Choose 1.60 when: the frame is rimless or semi-rimless, whatever the power — or the prescription sits in the moderate range and you want thinner without going premium.

A rimless frame has no rim: the bridge and arms are screwed through holes drilled in the lens, so the lens itself bears the mounting screws — which is why opticians fit a tough material there.

Illustrative · the shape of the principle, not measured data

1.67 — where thin starts to show

Somewhere above 6.00 diopters, a lens stops being something people look through and starts being something they look at. Edge thickness becomes visible in the frame; the eyes behind a strong minus lens look smaller, and larger behind a strong plus lens. 1.67 is where CLIFF answers that.

At these powers the difference is not subtle — a 1.67 lens is dramatically slimmer than the same prescription in 1.50, and it changes how the finished glasses look on the face. This is also where the range starts to narrow: 1.67 is made in Dynamix, Zenn and Zenn AI, and 1.74 in Zenn and Zenn AI alone — because a prescription strong enough to need the thinnest material deserves a surface calculated well enough to use it. A strong prescription magnifies design flaws exactly as it magnifies everything else.

Choose 1.67 when: the prescription runs from about 6.00 to 8.00, and how the glasses look matters as much as how they see.

1.74 — the ceiling

1.74 is the thinnest lens material CLIFF makes, reserved for the strongest prescriptions — up to −20.00 diopters of sphere. At those powers it is not a luxury; it is the difference between glasses a person is comfortable wearing in public and glasses they are not.

An honest note, because it earns trust: very high index materials disperse light a little more, and some wearers of strong prescriptions notice faint color fringing at the very edge of vision. That is physics, not a defect — and at the powers 1.74 serves, the trade is overwhelmingly worth it. What it is not worth is fitting 1.74 to a mild prescription, where it buys almost no thinness and gives away clarity for nothing. An optician who steers you to the lowest index that looks right is giving you the correct advice.

Unlike 1.67, which Dynamix also reaches, it is made only in Zenn and Zenn AI.

Choose 1.74 when: the prescription is above 8.00 — and at that point, don't hesitate.

Abbe number by index — the higher it is, the less the lens splits white light into colored edges. It falls as the index climbs: the catch that comes with a thinner lens.

From CLIFF's index data · Abbe by lens material

The rule that ties it together

Choose the lowest index that gives you a thickness you're happy with. Index buys thinness, not clarity — clarity comes from the design. That is why the money, at most prescriptions, is better spent one row up the design ladder than one row up the index table.

See the full range