You cannot get glasses online if you don’t know the prescription.
The optometry steps for wearing glasses need to be done in an offline physical store.
After the optometrist performs the test, the main parameters are the following data. You need to see an optician for prescription glasses. Only in this way can you get glasses that fit the person's prescription.
The terms are as follows:
Pupillary distance (PD)
The horizontal distance between the two points of the pupil center of the left and right eyes. Generally, there is no special note for PD on the prescription form. Indicates the far interpupillary distance of both eyes. Generally expressed by the English abbreviation "PD", the unit is millimeters (mm).
Sphere lens (SPH)
The degree of myopia, hyperopia and presbyopia. SPH is "-", which means myopia; SPH is "+", which means farsightedness or presbyopia. Spherical lenses are divided into concave lenses and convex lenses. Concave lenses are represented by "-" and are used to correct myopia; convex lenses are represented by "+" and are used to correct farsightedness.
Cylinder (CYL)
The degree of astigmatism.
Axis (AXIS)
The direction of astigmatism. Note: There is an axis of astigmatism only if there is a degree of astigmatism; there is no axis if there is no degree of astigmatism.
Corrected visual acuity (VA)
Refers to the visual acuity detected after wearing glasses.
Extended information:
Optometry must be accurate:
Optometry is the main basis for wearing glasses. The accuracy of the optometry is directly related to the success rate of the glasses prepared. First of all, the refraction must be accurate, and the upper and lower difference should not exceed 12.5 degrees of the prescription; secondly, the astigmatism axis must be accurate, and generally the axial difference should be limited to plus or minus 1 to 3 degrees; thirdly, the interpupillary distance must be accurate, and the pupil distance must be accurate. The distance should be equal to the optical center distance of the lens.
If you do not pay attention to the above-mentioned checks in optometry, the prepared spectacle lenses will cause adverse effects such as blurred vision, fatigue, dizziness, nausea, and even double vision. It is best to go to a professional eye hospital for refraction. For children or children who are wearing glasses for the first time, they must use dilated refraction to ensure accuracy.
You can also check if there are any problems with the fundus of your eyes. In short, it is right to go to the hospital. Many optical shops are not professional optometrists, and they do not have good equipment for optometry. The price of hospital optometry is less than 100 yuan, which is not expensive but the effect is much better.
Baidu Encyclopedia-Optics