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Lens Materials: Standard Plastic, Polycarbonate and Glass Compared

Written by Alvin · Manh Long Optical, 147A Le Duan, Cua Nam, Hanoi · Updated 17 September 2026

The first question at the counter is usually "what index." But index is only an optical number — it doesn't say what the lens is made of, how easily it breaks, or whether you'll see a color fringe at the edge. Those three come down to material. This page puts the materials side by side, plus two ideas customers rarely ask about: Abbe value and prism lenses.

Index and material are two different things

Index is a number that says how strongly a material bends light; the higher it is, the thinner the lens at the same prescription. But "1.56" or "1.67" isn't the name of one specific plastic — each index level on a price list is usually its own polymer formula, engineered to hit that exact refraction.

In other words: two 1.67 lenses from two different brands can still be different plastic formulas, with different durability and clarity. Our lens index guide has the full seven-level price table if you're comparing by prescription; this page is about what the lens is actually made from.

Standard plastic: where lens plastic started

Standard plastic — usually called CR-39 after its chemical name — was introduced in the 1940s to replace glass in everyday eyewear. Its index sits around 1.50, low compared to the higher levels on today's price list, but its Abbe value (clarity, see section 6) is among the highest of any lens plastic.

Most lenses at "1.56" and above on Manh Long Optical's price list are improved polymer formulas built on that same foundation, adjusted to hit a higher index — not raw CR-39. The higher the index, the more specialised the formula, and usually the higher the price.

Impact-resistant plastic (polycarbonate): who actually needs it

Polycarbonate is a plastic that resists impact far better than standard lens plastic — the same material used in safety goggles and small-aircraft windshields. It's also lighter, which matters if you wear glasses all day.

Manh Long Optical currently carries polycarbonate at index 1.59 from Essilor, 2,980,000d a pair (September 2026 pricing, frame not included). It's the recommended choice for active children, athletes, or anyone in work where the lens face takes hard knocks.

The trade-off: polycarbonate's Abbe value is lower than standard plastic, so at the lens edge — especially on large frames or high prescriptions — you may notice a faint color fringe. Most wearers barely notice it; in exchange you get a lens that's much harder to break.

Trivex: exists, but not common in Vietnam yet

Trivex is a material introduced in the early 2000s. It's nearly as impact-resistant as polycarbonate but has a higher Abbe value — meaning less color fringe at the edge — and is a touch lighter.

Manh Long Optical's current price list doesn't carry Trivex as a separate listed option. If you specifically need it, the reliable way to check is to ask at the counter so a technician can confirm what's currently available, rather than assuming.

Glass: why almost nobody sells it anymore

Glass lenses have a naturally high index and a high Abbe value, giving a very clear image. But they weigh nearly twice as much as a plastic lens of the same size, and on hard impact they tend to shatter into sharp pieces — a real risk to the eye.

For that safety reason, almost every optical shop today, including Manh Long Optical, no longer sells glass lenses for everyday eyeglasses.

Abbe value: the number nobody asks about, but it affects sharpness

Abbe value measures how much a material bends different colors of light apart from each other. The lower the number, the more white light splits into visible color fringes at the lens edge — usually a faint purple or blue tinge — most noticeable on large frames, high prescriptions, or high-contrast subjects like black text on white.

There's a common trade-off: the higher the index (the thinner the lens), the lower the Abbe value tends to be. This isn't an absolute rule — every brand has its own formula, and anti-reflective coating helps reduce visible fringing too — but it's why "get the highest index you can" isn't always the sharpest choice, especially for lower prescriptions that don't really need an ultra-thin lens.

Prism lenses: when they're used

A prism lens is ground with an added amount of prism to bend light before it reaches the eye. An eye doctor prescribes this when the two eyes don't aim at exactly the same point — for example mild strabismus or double vision — so both eyes receive the same image point and don't have to keep correcting for each other.

The amount is written on a prescription in prism diopters, along with a base direction (base up/down/in/out). This is a medical prescription detail, not a cosmetic upgrade. If your prescription includes a prism value, bring it to Manh Long Optical — our technician will recommend the right lens and frame to fit it correctly.

Sphere (SPH) and cylinder (CYL): lenses also correct different shapes of blur

Beyond material, a lens is also ground to correct two different shapes of blur: the spherical curve bends light evenly in every direction, used for nearsightedness and farsightedness (the SPH column on your prescription); the cylindrical curve bends light along one axis only, used specifically for astigmatism (the CYL and AXIS columns). Neither is related to material or index — they describe what shape the lens has to be for light to focus correctly on the retina. Our guide to reading a prescription covers both columns in detail.

So which material should you pick

A quick guide by need — the shop will still confirm against your actual eye test.

Common questions