Thinner, lighter, better - Are high index lenses worth it?

• Refractive index is a numerical measure of a material’s ability to bend light, which plays a key role in determining the final thickness of a prescription lens.
• Plastic and glass are the two of the most common lens materials, and each is available in varying levels of refractive index to suit different prescriptions.
• Prescription lenses made from high index materials are more comfortable for everyday wear, as they are lighter, thinner, and can offer more natural vision compared to standard lenses.

Prescription lenses can be customized in various ways to make glasses that are clear and comfortable to wear. This is important for people who require significant correction for myopia, hyperopia, astigmatism, as higher prescriptions result in thick, bulky lenses with vision distortions.

In order to overcome these challenges, materials for prescription lenses are available in different levels of refractive index. Lens index (or refractive index) is a number that describes how efficiently a lens material bends light. In simple terms, the lens index affects thick or thin your lenses will be. Because they focus light more efficiently, lenses of a higher index require less material to produce a lens of a given prescription, resulting in a thinner and lighter lens.

 For example, the standard material used to produce prescription lenses is CR-39 plastic, which has a refractive index of 1.50. A prescription lens made with a higher index material (e.g. 1.67) would be thinner and lighter compared to the CR-39 lens.

Spectacle lenses are generally made from either plastic or glass. Each material comes in different refractive indices suited for different prescriptions.

 Plastic Lens Index Chart

Glass Lens Index Chart

Plastic lenses are the most commonly used lens material today. They are lightweight, which improves comfort for everyday wear, and they are available in a wide range of refractive index options. Plastic lenses are also impact resistant, especially materials such polycarbonate and Trivex, making them a safe choice as they are less prone to shattering compared to glass.

Glass lenses offer exceptional optical clarity and superior scratch resistance, but they are heavier and more fragile than plastic lenses. Some people still prefer glass lenses, particularly those with very high prescriptions. As glass is available in higher refractive indices than plastic, this can allow lenses to be made thin enough to fit glasses frames, where high index plastic may not be adequate.

For the majority of people who wear glasses, plastic lenses are the most practical choice due to their comfort and safety. In rarer situations, glass lenses may offer an advantage by accommodating very high prescriptions.

High-index lenses are generally recommended for people with moderate to high prescriptions, typically stronger than ±3.00D. As prescription strength increases, standard lenses become thicker, heavier, and less comfortable. High-index materials help solve these issues by offering a slimmer and lighter alternative.

Rimless or semi-rimless frames expose the lens edges. High-index materials keep those edges thinner, making them suitable for stronger prescriptions. Besides, they can also choose larger or more fashionable frame.

• Thinner lenses: The higher the index, the thinner the lens for the same prescription. High-index lenses can significantly reduce thickness at the edge of the lens for glasses that correct myopia (nearsightedness), or thickness at the centre of the lens for glasses that correct hyperopia (farsightedness).
• Lighter weight: Thinner lenses reduce the overall weight of the glasses. It can improve comfort on the nose, reduce pressure on the ears and enhance overall wearability throughout the day.
• More natural look: Higher-index lenses reduce magnification (in farsighted prescriptions) and minification (in nearsighted prescriptions), resulting in a more natural appearance.

• More expensive – high index lenses generally cost more than standard lenses as they are manufactured from premium materials.
• More fragile – high index lens may potentially be more fragile than regular lenses.
• Potential vision distortion – high index lenses tend to have a lower Abbe number (a measure of how much a lens disperses light), which can cause colour fringing and distortion around the edges of the vision.

Choosing the right lens index can significantly improve your comfort, appearance, and overall eyewear experience. Whether you’re aiming for thinner lenses, lighter glasses, or a more stylish frame choice, high-index lenses offer a premium upgrade—especially for moderate to high prescriptions.

If you’re unsure which lens index is right for you, an optometrist or optician can help recommend the best material based on your prescription, lifestyle, and frame selection.