How to choose the right lenses index for your glasses
What's index lens?The refractive index of the lens indicates the efficiency of lens material on bending or refracting light. A higher refractive index indicates that light is more bended and spends more time on passing through the lens. Also, a higher refractive index can deal with higher prescription glasses. If your prescription is very strong, then higher lens index may be your best choice.
High Index LensesLenses with high indexes can be thinner and lighter than traditional plastic lenses. Compared with traditional lenses, highly index lenses can bend the light more efficiently, so they can be thinner while maintaining the same correction power.
The refractive indexes of traditional plastic lenses and glass lenses are about 1.5 and 1.52 respectively. Any lens material with a refractive index higher than these numbers are considered a highly index lens material.
How to Choose the Right Glasses LensDifferences among different lens indexes can generate great impacts. Thicker lenses are more affordable, but they can only handle lower vision correction demand. Thinner lenses are lighter and more fashionable, but the price is also higher. They can satisfy various vision correction demands, including higher prescriptions. This guidance will teach you how to read the prescription: How to Read Your Eyeglass Prescription
1.5 Index Lens – Standard lensIf you are looking for a more cost-efficient lens with a weak prescription, these lenses may be your correct answer. Lenses with this index can deal with prescriptions with an SPH correction of +/- 2.25 and lower or a CYL correction of +/- 1.50 and lower.
1.57 Index LensFor those with slightly stronger prescriptions, these lenses may be a better choice than standard lenses. These lenses are thinner and stronger than lenses with a 1.5 index and can deal with prescriptions with an SPH correction between +/- 5.00 and +/- 4.00 and a CYL correction of +/- 3.00 and lower.
1.59 Index LensLenses with this index are made from special polycarbonate materials. This means that they can provide 100% UV protection. They are more durable and resistant to shock, which make them an ideal choice for most people.
Sometimes, customers ordering rimless glasses or semi-rimless glasses containing 1.59 polycarbonate lenses may complain about color difference issues. Moreover, 1.59 polycarbonate lenses are more vulnerable than 1.50, 1.57 and 1.53 lenses since its material is softer than others. However, you can choose some lens coatings to protect the lens. Please refer to this guidance to learn about how to choose the lens coating: Lens coatings: UV, Scratch resistant, Anti-reflective
1.6 Index LensThese fashionable ultra-thin lenses are ideal for strong prescriptions or very thin eyeglasses frame. These lenses are suitable for prescriptions with an SPH correction between +/- 4.25 and +/- 6.75 and a CYL correction between +/- 2.25 and +/- 3.00.
1.67 Index LensThese lighter and thinner lenses can avoid distortion of eyes due to stronger prescriptions. If you have a very strong prescription, this may be your best choice. We usually recommend that these lenses are applicable to prescriptions with an SPH correction between +/- 7.00 and +/- 9.00 and a CYL correction between +/- 3.25 and +/- 4.00.
1.74 Index Lens
Our thinnest lenses are designed for prescriptions with the highest power. These lenses are applicable to prescriptions with an SPH correction of +/- 9.25 and above and a CYL correction between +/- 4.25 and +/- 6.00.
You can refer to this graph for choosing correct lenses with the optimal refractive index:
Although lenses with high refractive indexes are thinner than traditional lenses, their final thickness still depends on your prescription and some other factors, including: your Pupillary Distance(How to Measure Your PD(Pupillary Distance) ), shape of the glasses frame, correction power, astigmatism power and axis, spherical or aspherical lenses and so on.
People looking for thinner lenses should pay more attention on dimensions and shape of the glasses frame. Thick lenses, especially those with high refractive indexes, can distort our eyes and the eye area. Therefore, people wearing thick lenses should choose round frames or oval frames to reduce such distortion as much as possible.
Except lens refractive index, the abbe number should also be considered. The abbe number is a number used for evaluating the dispersive power of the optical system. A small abbe number means large dispersive power; on the contrary, larger abbe numbers indicate that the dispersive power is small.
The abbe number of lenses with 1.50 refractive indexes can reach 58. However, when it comes to lenses with 1.74 or a higher refractive index, the abbe number can drop to only 32-36. This means that thinner lenses can lower the true feeling of eyes on colors and reduce the comfort level since they have lower abbe numbers.