Plastic lenses are the standard for most eyewear, and the simple answer to whether they are bad for your eyes is generally no, though certain materials have specific drawbacks for visual quality. “Plastic lenses” refers to a family of materials, including standard CR-39, impact-resistant polycarbonate, and newer high-index plastics, all of which offer distinct safety and comfort advantages over traditional glass. The choice of material introduces trade-offs between thinness, weight, safety, and optical clarity. The overall quality of your vision is determined by selecting the appropriate plastic compound for your specific prescription and lifestyle needs.
Protecting Your Eyes: The Safety Advantages of Plastic Lenses
Modern plastic lenses provide an exceptional measure of physical protection that traditional glass lenses simply cannot match. Materials like polycarbonate and Trivex are engineered to be highly impact-resistant, making them virtually shatter-proof under typical force. Polycarbonate lenses are up to 10 times stronger than standard plastic and are the material required for most safety glasses and children’s eyewear due to this superior durability. This resistance to shattering prevents severe eye injury that can occur if a glass lens breaks into sharp fragments upon impact.
Beyond physical integrity, many contemporary plastic lenses incorporate a powerful defense against environmental damage. Polycarbonate and Trivex materials naturally block 100% of the sun’s harmful ultraviolet A (UVA) and ultraviolet B (UVB) rays. This built-in UV protection is important for long-term ocular health, as cumulative exposure to UV radiation is linked to the development of eye conditions like cataracts and macular degeneration. Standard CR-39 plastic does not inherently block all UV light, but a protective coating can be easily added. The lightweight nature of plastics also reduces strain on the nose and ears, contributing to better comfort for all-day wear.
Optical Quality: Clarity, Distortion, and Eye Strain Concerns
While plastic lenses offer superior safety, certain material properties can introduce optical compromises that may contribute to eye strain, particularly in stronger prescriptions. One such phenomenon is chromatic aberration, sometimes described as “color fringing,” where the lens fails to focus all colors of light to a single point. This effect is quantified by the Abbe value, where a lower number indicates greater light dispersion and more noticeable color fringing. Polycarbonate, known for its impact resistance, has a relatively low Abbe value of around 30, meaning some wearers may perceive a slight rainbow halo around high-contrast objects, especially toward the periphery of the lens. This distortion is often more apparent in high-index plastics, which are designed to be thin but sacrifice some optical clarity for a reduced profile, potentially leading to eye fatigue.
Plastic is also inherently softer than glass, making it susceptible to surface scratches. Even small scratches can disperse light, causing glare and visual distraction that interferes with clear vision. For this reason, plastic lenses require a factory-applied hard coat to improve durability and maintain the lens’s integrity. Furthermore, plastic lenses have a high surface reflectance, meaning they reflect more light than glass, which can be bothersome to the wearer and create a cosmetically unappealing glare. To mitigate this reflection and improve light transmission, an Anti-Reflective (AR) coating is highly recommended, though this adds to the overall cost and introduces another layer that can potentially scratch or peel over time.
Navigating the Options: How Different Plastic Materials Compare
The broad category of plastic lenses includes several distinct materials, each balancing thickness, weight, safety, and optical clarity differently.
CR-39
CR-39 (Columbia Resin 39) is the original standard plastic, offering excellent optical clarity with a high Abbe value of 58, which means it has very little chromatic aberration. However, CR-39 is thicker than modern alternatives and lacks built-in UV protection and high impact resistance, making it better suited for low prescriptions and less active use.
Polycarbonate
Polycarbonate is the material of choice when safety and thinness are the primary concerns, due to its exceptional impact resistance and high refractive index (1.586), which allows for thinner lenses in stronger prescriptions. The trade-off is its low Abbe value of 30, which can lead to more noticeable chromatic aberration compared to other plastics.
Trivex
Trivex is a newer, premium material that provides a better balance. It offers impact resistance comparable to polycarbonate but has a superior Abbe value of 43 to 45. This results in better optical clarity and fewer chromatic aberrations than polycarbonate, while also being one of the lightest lens materials available.
High-Index Plastics
High-Index Plastics (refractive indices of 1.60 and above) are used for very strong prescriptions to achieve the thinnest possible lens profile. While they reduce thickness, they generally have lower Abbe values (in the 30s) than CR-39 or Trivex, requiring the wearer to accept a greater risk of peripheral distortion for the benefit of a cosmetically thinner lens.