One of the important parameters is the radius of base curvature, in the recipe it is denoted BC, R. What does this indicator mean and what happens if you do not follow it?
Each person's cornea has its own radius of curvature, and the contact lens must match this. It needs to remain mobile on the eye, but at the same time not put too much pressure on it. Thus, the radius of the base curvature of a contact lens is the curvature of its posterior surface, corresponding to the shape of the cornea of the eye.
This indicator is indicated measured in millimeters and, as a rule, has values from 7.8 to 9.5 mm. The standard BC value is 8.6 mm, while in optics shops and online stores you can usually easily find contact lenses with a parameter from 8.3 to 8.8 mm.
Only a professional ophthalmologist using special equipment can understand which value is right for you. For this, a study is carried out, which is called autorefractometry. It provides extensive information about the state of the organs of vision and the features of the visual system. This diagnosis takes quite a bit of time, just a few minutes.
Incorrectly fitting lenses can cause a lot of trouble: from simple discomfort to impaired tear production, blurred vision and serious eye diseases.
If the lens fit is not suitable, the eyes will be affected. Too convex can compress the vessels and cause excessive tension in the eye muscles, because their mobility in front of the eyes will be limited. This is expressed, first of all, in a strong reddening of the eyes. In addition, dryness and even inflammation may occur, since a lens pressed too tightly against the cornea does not allow the tear to move. Too flat, with too large a radius of curvature, too mobile and loose on the cornea. They do not provide sufficient correction, vision may be blurred, and the lenses may even fall out of the eyes. There may also be increased tearing and pain when blinking, as a loose lens touches the upper eyelid.
If you already know the radius of curvature of a certain brand, but want to switch to another, ask your doctor for advice – different brands of lenses can have a different fit on your eyes!