What are the different materials for eyeglass lenses?
There are 5 main types of lens materials for eyeglasses and sunglasses. Each type of lens material can help correct refractive errors such as nearsightedness, farsightedness, astigmatism, or presbyopia.
Before going into the different materials, it can be good to understand the index of refraction. Some materials are categorized by the index of refraction, which indicates how fast light travels through a given material.
Essentially, the higher the refractive index of a material, the slower light moves through it, which results in a greater bending (refracting) of light rays. With a higher refractive index, less lens material is required to bend light to the same degree as a lens with a lower refractive index.
In other words, for any eyeglass prescription, a lens made of a material with a high-refractive-index will be thinner than a lens made of a material with a lower refractive index.
Now to the 5 main materials:
Glass lenses are among the best lens material in providing visual clarity and being highly scratch resistant, due to their hard surface.
However, glass lenses are heavy, thick, and have a lower impact resistance. In many cases, glass lenses have to be specifically treated to comply with impact-resistant regulations and can not always fit in every frame design.
Plastic (CR-39) is the standard glasses lens material. Compared to glass lenses, plastic lenses are lighter and less likely to shatter as easily. Plastic lenses offer great optics and vision correction for refractive errors and block out 80% of UV light.
However, CR-39 plastic lenses tend to be thicker than other plastic materials as they have a lower index of refraction.
Polycarbonate lenses have a higher index, higher impact resistance, and superior UV protection than standard plastic lenses. Polycarbonate lenses are more prone to scratches and thus adding an anti-scratch coating will help keep your lens clear.
These thinner and durable polycarbonate lenses are for sure a popular choice among glasses wearers. If you have an active lifestyle and need safety glasses for work or leisure, then polycarbonate lenses are a great pick. They are also recommended for kids'Glasses.
Glasses that require a higher prescription and are fitted with polycarbonate lenses can cause chromatic aberration (see image below). Chromatic aberration is the distortion of an image caused by the lens not being able to focus all colours on the same point. This happens because the lenses have a lower abbe value which means a higher dispersion of light - hence the light does not focus on one exact point.
Trivex lenses are another great choice for children’s eyewear and safety glasses as they have a higher impact resistance. Trivex lenses are also thinner and lightweight, offering exceptional optics and very low chromatic aberration due to their higher abbe value. This means that trivex lenses can provide a clearer and crispier visual experience.
Just like the CR-39, the trivex lens has a lower index of refraction, causing the lens to be thicker with a higher prescription.
High index lens materials are the thinnest and lightest of them all. High index lenses can be used for stronger prescriptions as they look more aesthetically pleasing with thinner lenses. High index lenses bend light more efficiently as they have a higher index of refraction.
High index lenses have superior optics and impact resistance but these factors can depend on the type of high index material used - glass or plastic. Like many other lens materials, high index lenses provide quality UV protection.