For the first time to wear reading glasses, it is necessary to know about the pupil distance of the near pupil (pupil distance). Due to the aggregation effect of the human eye when it looks close, the pupil distance of the near pupil (take the reading distance of 33cm as an example) is 4~6mm smaller than that of the far pupil distance (head distance) of PD.
Reading glasses have an important optical index OCD (the horizontal distance between the optical center of the two lenses). OCD and PD should be as consistent as possible.
According to the national standards, there is a difference between the two. According to the relevant national standards, the tolerance of ±3mm for sunset red reading glasses, that is to say, the OCD value of the reading glasses should be between 59-65mm for a customer who USES PD=62mm.However, the best solution is to choose glasses with an OCD value less than pupil distance. Glasses with an OCD value much greater than pupil distance will cause sore eyes, fatigue and inability to concentrate vision.
If the pupil distance is too small and too large, so that the lens cannot be selected, and the matching lens cannot be assembled (no oversized frame, oversized piece), then the focal-free reading glasses are the best choice.
Use the distance
As the characteristic of presbyopia is the eye to see far, see close adjustment ability is poor.For example, when the user's visual acuity diopter is + 4.00d (commonly known as 400 degrees), its visual acuity regulation ability can only function within a few centimeters. A pair of reading glasses only supplements the user's visual acuity with a fixed diopter, but does not enhance the user's visual acuity regulation.
That is to say, the user is not fixed to wear a fixed degree of reading glasses, but should use their own vision based on the distance to choose the appropriate degree of reading glasses.For example, when reading a book, reading a newspaper or writing, the use distance is 33cm, which is called reading distance.