Which lens material has the highest Abbe value?

Crown glass has the highest Abbe value at 59, closely followed by CR-39 at 58. Among plastic-only materials, CR-39 has the highest Abbe value. Polycarbonate has the lowest Abbe value (30) of commonly used materials, meaning it produces the most chromatic aberration.

Which lens material is the lightest?

Trivex is the lightest common ophthalmic lens material with a specific gravity of 1.11. Polycarbonate is next at 1.20. CR-39 is 1.32. High-index materials range from 1.30 to 1.50. Glass is the heaviest at 2.54, approximately twice as heavy as plastic.

When should I recommend high-index over polycarbonate?

Recommend high-index when the patient's primary concern is lens thickness and they have a prescription above ±4.00 D. Recommend polycarbonate when impact protection is the priority (children, safety, sports) or when the patient needs a budget-friendly option that is thinner than CR-39. For patients needing both impact resistance and good optics, Trivex is the best compromise.

Lens Material Comparison Guide for ABO

Complete Material Comparison

Choosing the right lens material is one of the most important decisions in dispensing. Each material has distinct strengths and weaknesses. This guide provides a comprehensive comparison to help you match materials to patient needs.

Side-by-Side Properties

Material	Index	Abbe	SG	Impact	UV	Best For
CR-39	1.498	58	1.32	Moderate	Partial	Low Rx, tinting, best optics
Polycarbonate	1.586	30	1.20	Excellent	100%	Safety, children, sports
Trivex	1.532	43-45	1.11	Excellent	100%	Rimless, premium safety
1.60 hi-index	1.60	36-42	1.30-1.37	Moderate	Varies	Moderate Rx
1.67 hi-index	1.67	32	1.35-1.40	Moderate	Varies	High Rx
1.74 hi-index	1.74	33	1.46-1.50	Moderate	Varies	Very high Rx
Crown glass	1.523	59	2.54	Poor	Partial	Industrial, heat exposure

Decision Framework by Patient Need

Priority: Safety/Impact Protection

Choose polycarbonate (best value) or Trivex (better optics). Required for:

Children under 18
Safety/industrial eyewear (ANSI Z87.1)
Sports eyewear
Functional monocular patients

Priority: Optical Clarity

Choose CR-39 (Abbe 58) or glass (Abbe 59) for the clearest vision. Best for:

Patients sensitive to chromatic aberration
Low prescriptions where thickness is not a concern
Upgrading from polycarbonate when color fringing is a complaint

Priority: Thin and Light

Choose high-index (1.67 or 1.74) for thinnest profile, or Trivex for lightest weight. Best for:

High prescriptions (±6.00 D and above)
Patients concerned about lens thickness and cosmetics
Large frame selections

Priority: Custom Tinting

Choose CR-39. It accepts dye the most evenly and in the widest range of colors and densities. Best for prescription sunglasses and fashion tints.

No single material is best for every patient. The ABO exam tests your ability to match materials to patient needs. Remember: CR-39 = best optics, polycarbonate = best impact, Trivex = best balance, high-index = thinnest, glass = best scratch resistance.

Common Exam Comparisons

Abbe Value Rankings (Highest to Lowest)

Glass: 59
CR-39: 58
Trivex: 43-45
1.60 hi-index: 36-42
1.74 hi-index: 33
1.67 hi-index: 32
Polycarbonate: 30

Weight Rankings (Lightest to Heaviest)

Trivex: 1.11
Polycarbonate: 1.20
CR-39: 1.32
1.60-1.67 hi-index: 1.30-1.40
1.74 hi-index: 1.46-1.50
Glass: 2.54

When a patient asks for "the thinnest lens," remember that material choice is only part of the equation. Frame size, lens shape, minimum edge or center thickness, and aspheric design all affect the final result. A smaller frame with 1.60 index can be thinner than a large frame with 1.74 index.

Always recommending the highest-index material available. For low prescriptions (under ±3.00 D), the thickness difference between CR-39 and 1.74 is barely noticeable, but the patient pays significantly more and gets worse optical quality. Match the material to the prescription strength and patient priorities.

Key Takeaways

No single lens material is best for all situations; match material to patient needs
Impact protection: polycarbonate or Trivex
Optical clarity: CR-39 or glass (highest Abbe values)
Thinnest lenses: 1.67 or 1.74 high-index
Lightest lenses: Trivex (SG 1.11)
AR coating is essential for high-index materials; scratch coat for polycarbonate