Lens Thickness and Refractive Index
The thickness of the lens is related to the refractive index. The higher the refractive index, the thinner the lens. You can choose the lens that is more suitable for you according to your own habits and preferences.
How to Choose The Index
If you don't know how to choose the Refractive Index,you can refer to these informations,and you can get the most comfortable prescription glasses.
How to Read Your Prescription
‘+’ or ‘-‘
‘+’ – Shows if you are long sighted (longsightedness)
‘-‘ – Shows if you are short sighted (shortsightedness)
If your Sphere (SPH) is ‘+’,you are farsighted,please tell us that after you put on the glasses, do you see further clearly or see near clearly compared with not wearing glasses.
Each row of an Rx has three main sections: Sphere (SPH), Cylinder (CYL), and AXIS. The SPH section corrects nearsighted or farsighted vision. The CYL and AXIS sections correct an astigmatism.
There may also be a fourth section on the Rx , NV-ADD (for Near Vision-Reading ADDition), which could be used to order a pair of bifocal or progressive glasses with a close-up vision section in the bottom part of the lens.
The SPH, CYL, and NV-ADD numbers will always have a plus or minus sign.
How to Measure Your PD
PD stands for Pupillary Distance, which is the measurement from the center of one pupil to the center of the other. Your PD is an important factor and tells you where you look through the lens of your glasses and should be as accurate as possible. For people with strong prescription, this is especially important. You can normally find your PD on your prescription. Generally speaking, the PD numbers for adults stays the same. The average PD range for adults is 57-72 mm and for kids is about 43-58 mm.
Your pupillary distance (PD) is the measurement of the distance between your pupils.
This is needed for the manufacturer of the eyeglasses to know where to place the optical center on each lens, so you can see well with the glasses.