When we buy contact lenses, we often only ask the businesses how many degrees they need, but in fact, there are many parameters of contact lenses, which have a certain impact on the wearing effect, so we should pay more attention to them. So what does the BC on the package mean?
BC (base curve) refers to the radian of the inner surface of the contact lens, in mm. When the base arc is large, it indicates that the inner surface is relatively smooth, and when the base arc is small, it indicates that the inner surface is relatively curved. Generally speaking, the common contact lens base arc in the market is mostly between 8.4-8.6, which is also in line with the average curvature of our eyes.
When the lens base arc does not match the eyeball base arc, it will affect the comfort of wearing. When the lens base arc is larger than the eyeball base arc, the adhesion of the lens is not high, and it is easy to shift or even fall out of the eye; conversely, if the lens is tightly attracted to the eyeball, it will cause anoxia and damage to the cornea. In a few people, the basic arc of the eyeball is not within the range of average radian, so they will feel uncomfortable when using it.
To verify whether the base arc is properly tightened, you can use clean fingers to gently push the edge of the lens, and it is easy to slide away, indicating that the base arc is large, and how to push it is too tight, only part of it is just suitable. When selecting the base arc, it can be slightly larger, and can be adapted within 0.2mm difference, but it must not be smaller.
If you have comfortable contact lenses, you can buy them directly according to the parameters marked on the product. If you have never contacted or used contact lenses, it is recommended to go to the hospital to check the eye data in detail. In case of emergency, 8.6MM lenses can be purchased preferentially, with a wider range of application.