# What Does The Radius Of Curvature Of Lenses Mean?

## Video: What Does The Radius Of Curvature Of Lenses Mean?

The radius of curvature of contact lenses is a parameter that determines their size. If it is chosen incorrectly, when wearing such lenses, a person will experience inconvenience, and his vision may deteriorate significantly.

## How is the radius of curvature of lenses determined?

The radius of curvature of the lens will depend on the structure of the human eyeballs. Since the lens is positioned on the cornea of ​​the eye, it must follow its shape as closely as possible. The human eyeball has approximately the following indicators: the length of the eye equator (the largest circumference of the eye in the frontal plane) is 23.6 mm, the length of the optical axis is 24 mm, and the vertical diameter of the eye is 23.4 mm. For a person with such standard parameters, the radius of curvature will be 8, 6. Lenses with indicators from 8, 3 to 8, 8 can be easily found on sale.

If the radius of curvature deviates significantly from the average norm, the lenses must be made to order. Their sketch is drawn up in consultation with an ophthalmologist. The doctor determines the desired radius of curvature of the lens in a way called "autorefractometry". A specialist examines the cornea of ​​the eye using computer diagnostic methods. Autorefractometry is based on the principle of infrared light emission. The resulting image of the light beam before and after its reflection from the retina is recorded by special sensors. In addition to the radius of curvature of the lens, the difference in refraction (the refractive power of the optical system of the eye, expressed in diopters) between the eyes and the magnitude of astigmatism (inability of the eyes to correctly focus) are also determined. An infinitely distant image is used as a fixation point in the study.

## What to do if contact lenses don't fit

In the event that the lenses have already been purchased, and the radius of curvature does not fit, you need to proceed as follows. If this difference does not exceed 0.2, doctors usually advise wearing such lenses, provided that discomfort is not felt. If this deviation exceeds 0, 2, they cannot be worn. In the event that a person wears more convex contact lenses, their mobility will be difficult. The blood vessels will squeeze and this will inevitably lead to reddening of the eyes. The eyeballs will be in constant tension, and tear exchange disorders may appear. The threat of inflammation will increase, vision will be unstable.

In the event that the radius of curvature is higher than the required value, contact lenses will be too mobile. They can easily fall out of the eyes, harm the cornea, and cause watery eyes. Flat lenses easily move away from the cornea, a person will not be able to see anything. Since they touch the upper eye muscles, pain will appear when blinking.