Spectacle Lens Materials and Coatings: CR-39, Polycarbonate, Trivex, High Index, Abbe Value and Blue-Cut
Last updated: November 2026
RPC Rounds for Optometrists · B.Optom study guide
Choosing the lens material is one of the most important dispensing decisions: it decides thickness, weight, safety, optical quality and price. Learn the four numbers for each material (refractive index, Abbe value, density and impact resistance) and you can explain every recommendation to a patient.
Comparing lens materials
| Material | Refractive index | Abbe value | Density (g/cm³) | Notes |
|---|---|---|---|---|
| Crown glass | 1.523 | 59 | 2.54 | Excellent optics and scratch resistance; heavy; shatters; rarely used now |
| CR-39 (allyl diglycol carbonate) | 1.498 | 58 | 1.32 | Standard plastic: light, good optics, cheap; scratches without a hard coat |
| Mid-index plastics | 1.53–1.56 | 36–45 | about 1.2–1.3 | Slightly thinner than CR-39 |
| Trivex | 1.53 | 43–45 | 1.11 | Lightest; impact resistant like polycarbonate with better optics; good for rimless and children |
| Polycarbonate | 1.586 | 30 | 1.20 | Very impact resistant (children, sports, safety, one-eyed patients); blocks UV; lower Abbe gives colour fringes |
| High-index 1.60 | 1.60 | about 36–42 | about 1.3 | Thinner for moderate powers |
| High-index 1.67 | 1.67 | about 32 | about 1.35 | Thinner for higher powers |
| High-index 1.74 | 1.74 | about 33 | about 1.47 | Thinnest plastic; high powers |
| High-index glass | 1.7–1.9 | about 30–40 | up to about 4.0 | Very thin but heavy |
- Refractive index: higher index bends light more, so the same power needs flatter curves and a thinner lens.
- Abbe value (constringence): the higher the number, the less chromatic aberration. Values under about 40 can cause colour fringes when looking off-axis, especially in high powers; good centration helps.
- Reflection rises with index (about 4% per surface for CR-39, more for 1.74), so high-index lenses need an anti-reflection coating.
- Impact resistance: polycarbonate and Trivex are the materials of choice for children, sports, safety eyewear and anyone with one useful eye.
Coatings and treatments
| Coating | What it does | Advice |
|---|---|---|
| Hard (scratch-resistant) coat | Protects plastic surfaces | Essential on CR-39, polycarbonate and high index |
| Anti-reflection (AR, multicoat) | Destructive interference reduces reflections to under about 1% | Reduces ghost images and glare (night driving, screens); improves appearance; clean with a microfibre cloth |
| Hydrophobic and oleophobic top coats | Repel water and grease | Easier cleaning |
| UV protection | Blocks ultraviolet up to about 380–400 nm | Polycarbonate, Trivex and most high-index lenses block UV inherently |
| Photochromic | Darkens in UV light, clears indoors | Slower to clear in heat; activate less behind car windscreens (UV is blocked) |
| Tints and polarised lenses | Reduce brightness; polarisers cut reflected glare | Polarised lenses help driving and water sports; tints over about 75–80% absorption are unsuitable for driving, especially at night |
| Mirror coatings | Reflect light for comfort and appearance | Cosmetic and outdoor use |
| Blue-light filtering ("blue-cut") | Reduces some short-wavelength visible light | A 2023 Cochrane review found no clear benefit for eye strain, sleep or eye health; do not oversell |
Choosing the material: a quick guide
| Patient | Suggested material |
|---|---|
| Child, sports, one-eyed patient, safety use | Polycarbonate or Trivex |
| Rimless or drill-mount frames | Trivex or polycarbonate (resist cracking at drill holes) |
| Low power (up to about ±2.00 D) | CR-39 with hard and AR coats |
| Moderate power (±2 to ±4 D) | 1.60 index |
| High power (over ±4 to ±6 D) | 1.67 or 1.74 with AR coat and a small frame |
| Sensitive to colour fringes | Higher Abbe material (CR-39, Trivex) and accurate centration |
For lens designs (aspheric, bifocal, progressive) see spectacle lens designs.
Practical pearls
- When a patient complains of colour fringes with new high-index lenses, check the centration and fitting height before blaming the material.
- Recommend AR coating with every high-index lens: reflections increase with index and spoil the thinner look.
- For a child with one good eye, polycarbonate or Trivex is not optional: it is a safety requirement.
Where students slip
- Saying high index always means lighter: high-index glass is heavy.
- Overselling blue-cut lenses as protection against eye disease.
- Using polycarbonate for a patient bothered by off-axis colour fringes without explaining the Abbe trade-off.
Test yourself: flip cards
Quick quiz
For daily counter use, see the lens types comparison and order checklist and the sunglasses, polarised and photochromic lens guide.
Related: Eyeglass Lens Coatings Guide Ahmedabad, Spectacle Dispensing Reference: PD, Fitting Height, Tolerances, Computer Vision Syndrome Ahmedabad, Sports Eye Protection: Cricket, Badminton, Squash and Swimming Eye Safety, Geometric and Physical Optics for Optometrists: Lenses, Prisms, Interference and Polarisation. Back to the optometry curriculum.
Key sources
- Jalie M. Ophthalmic Lenses and Dispensing. 3rd ed. Butterworth-Heinemann; 2008
- Brooks CW, Borish IM. System for Ophthalmic Dispensing. 3rd ed. Butterworth-Heinemann; 2007
- Singh S, et al. Blue-light filtering spectacle lenses for visual performance, sleep and macular health in adults. Cochrane Database Syst Rev. 2023
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