Choosing new eyeglasses involves selecting a lens material that impacts comfort, durability, and visual performance. The material determines how light is bent, the final lens thickness, and its resistance to impact. There is no single “best” material, as the right selection depends on the wearer’s specific prescription strength, daily activities, and budget. Understanding the differences between standard plastics, safety materials, and specialized high-index options is the first step toward an informed decision.
Comparing Standard and Safety Materials
The most common material, standard plastic, often designated as CR-39 (allyl diglycol carbonate), has been a staple in eyewear for decades. It offers excellent optical clarity and is the most affordable option for those with mild prescriptions. However, CR-39 has the lowest density and refractive index among modern materials, meaning it results in the thickest and heaviest lens for any given prescription.
Polycarbonate lenses represent the industry standard for safety due to their superior impact resistance. This material is approximately ten times more shatter-resistant than CR-39 and meets the requirements for safety eyewear, making it a popular choice for children’s glasses and sports eyewear. Polycarbonate is also lighter and thinner than CR-39 for the same prescription, with a refractive index of about 1.59.
Trivex offers a combination of high impact resistance and improved optical clarity compared to polycarbonate. It is slightly lighter than polycarbonate, which reduces the overall weight of the glasses. For those prioritizing both safety and a sharper image, Trivex provides a middle ground, although it is more expensive than standard polycarbonate.
When to Choose High-Index Lenses
The refractive index measures how efficiently a material bends light; a higher index number means light is bent more sharply. For individuals with strong prescriptions, such as high degrees of myopia or hyperopia, a high-index lens is recommended. These materials allow the lens to be significantly flatter and thinner than one made from a standard material like CR-39.
High-index plastics, such as those with indices of 1.67 or 1.74, require less material to achieve vision correction. This reduction in thickness makes the lens cosmetically more appealing and reduces the overall weight of the final eyewear. While these lenses are thinner, they come with a higher price tag compared to standard plastic or polycarbonate. They minimize the “coke bottle” appearance often associated with strong prescriptions.
Optical Clarity, Weight, and Final Selection
Optical clarity is determined by a property called the Abbe value, which measures a material’s ability to disperse light into different colors, known as chromatic aberration. A higher Abbe value indicates less light dispersion and better clarity, especially noticeable in peripheral vision or around bright lights. CR-39 has one of the highest Abbe values (around 58), giving it a distinct advantage in raw optical quality.
Polycarbonate, while excellent for safety, has the lowest Abbe value (around 30), meaning it has the greatest light dispersion and is the most likely to introduce noticeable chromatic aberration. Trivex offers a superior Abbe value (around 43) compared to polycarbonate, balancing impact resistance with better visual fidelity. High-index materials fall in the lower-to-mid range of Abbe values, trading thinness for potential clarity.
If a prescription is mild and maximum clarity is the goal, CR-39 remains an outstanding, low-cost choice. For active individuals, children, or those needing safety glasses, polycarbonate offers superior impact protection and thinness for a reasonable cost. Trivex is a premium choice for those who need impact resistance but want better optical performance than polycarbonate. For people with strong prescriptions, high-index lenses are necessary to achieve an aesthetically pleasing and comfortable thin profile, accepting reduced clarity in exchange for weight and thickness reduction.