Q: How do you know the thickness you need?
A: Dear Suzanne Delapena,
The feature of distance lenses
If you are farsighted, the lenses are usually thinner at the edge and thicker at the center.
The feature of reading lenses
If you are nearsighted, your lenses are usually thinner at the center and thicker at the edge.
The recommend of the index
If your power is around -2.00, choose 1.56 index, it will be around 3mm
If your power is around -4.00, choose 1.61 index, it will be around 3 to 4mm
If your power is around -6.00, choose 1.67 index, it will be around 4 to 5mm
If your power is more than that, choose thinnest lens, 1.74 index. It will be around 5mm to 8mm.
What affect lens thickness
Index
To understand this, you should know that lens thickness is generally categorized into 4 groups, or we normally call it “index” ie 1.56, 1.61, 1.67 and 1.74. The higher the index, the thinner the lens is.
2.Prescription
Prescription This is easy to understand. For the same index, the higher the prescription, the thicker the lens is.
3.Pupillary Distance
Pupillary distance is the distance between two pupil centers. The idea is to align the optical center to the pupillary center so that we can minimize distortion and optimize the vision. The wider the pupillary distance, the lens will be thinner.
4.Frame size
Since the lens thickness increases exponentially, as the frame size gets larger, it will utilize the side of the lens, which is also the thicker part. Therefore, for the same prescription and lens index, the larger the frame, the thicker the lens will turn out.