What Is Polycarbonate?
Polycarbonate is a thermoplastic lens material known primarily for its exceptional impact resistance. Originally developed for aerospace applications (astronaut helmet visors, aircraft windows), it became a standard ophthalmic lens material in the 1980s. It is the default choice for safety eyewear, children's glasses, and sports eyewear.
Key Properties
| Property | Value | Significance |
|---|---|---|
| Index of refraction | 1.586 | Thinner than CR-39 for same power |
| Abbe value | 30 | Lower optical clarity; more chromatic aberration |
| Specific gravity | 1.20 | Lighter than CR-39 |
| Impact resistance | Exceptional (highest among common materials) | Virtually shatterproof |
| UV protection | Inherent 100% UV-A and UV-B blocking | No additional UV coating needed |
Advantages of Polycarbonate
- Unmatched impact resistance: Meets ANSI Z87.1 high-velocity impact standards
- Built-in UV protection: Blocks 100% of UV without additional coating
- Thinner than CR-39: Higher index (1.586) means approximately 20% thinner lenses
- Lightweight: Lightest of the common lens materials (specific gravity 1.20)
- Ideal for rimless and semi-rimless frames: Does not crack at drill holes
Polycarbonate is the MOST impact-resistant common ophthalmic lens material. It is required for OSHA safety eyewear and is the recommended material for children under 18, sports eyewear, and patients with only one functioning eye (functional monocular patients).
Limitations of Polycarbonate
- Low Abbe value (30): More chromatic aberration than CR-39 or Trivex; patients with high prescriptions or those sensitive to color fringing may notice it
- Soft surface: Scratches easily without a scratch-resistant coating (hard coat is essential)
- Stress marks: Internal stress from injection molding can cause visible birefringence under polarized light
- Difficult to tint: Does not accept conventional dyes; requires special surface coating or in-mold tinting
- Surface distortion: Lower optical quality compared to cast materials like CR-39
When to Recommend Polycarbonate
- Children under 18: Impact protection is essential for active young patients
- Safety/industrial eyewear: Meets ANSI Z87.1 requirements
- Sports eyewear: Protects against balls, rackets, and impacts
- Functional monocular patients: Protecting the remaining good eye is critical
- Rimless/semi-rimless frames: Resists cracking at drill points
- Patients wanting thinner lenses on a budget: Thinner than CR-39, often less expensive than high-index
Always recommend a premium scratch-resistant coating (hard coat) with polycarbonate lenses. The material's soft surface makes it prone to scratching, which is the most common patient complaint. Many labs apply hard coat as standard on polycarbonate, but verify before dispensing.
Recommending polycarbonate for high-minus prescriptions purely for thickness. While polycarbonate is thinner than CR-39, its low Abbe value (30) causes noticeable chromatic aberration in higher prescriptions. For prescriptions above -6.00 D, high-index materials or Trivex may provide better visual quality.
Key Takeaways
- Polycarbonate (n=1.586, Abbe 30) is the most impact-resistant ophthalmic lens material
- Mandatory for safety eyewear; recommended for children and sports
- Built-in 100% UV protection with no additional coating needed
- Lower optical clarity (Abbe 30) than CR-39 or Trivex
- Requires scratch-resistant coating due to soft surface