Radius of curvature of contact lenses
Hereditary diseases, unhealthy lifestyle, stress, prolonged sitting in front of a monitor screen can leave their negative imprints on the quality of vision. Therefore, over time, many people have to use aids to ensure quality vision - glasses or contact lenses. Due to our unique lifestyle, wearing glasses is not suitable for everyone.
For example, athletes, actors, circus performers, diesel locomotive drivers, due to the nature of their work, cannot afford to wear glasses. And modern people, who primarily value comfort and freedom of action in everyday life, make their choice in favor of contact lenses.
The content of the article
What is the radius of curvature
This concept refers to the ratio of the radius of the inner surface of the lens to its outer diameter. This numerical designation is used to ensure that the product, when fixed to the eyeball, follows its contour as clearly as possible. Otherwise, with daily use of lenses, uncomfortable sensations, irritation of the surface of the cornea of the eye, and even the occurrence of various diseases may occur.
This is indicated on the individual packaging BS or BC. In addition, contact lenses with a properly selected radius of curvature provide a clearer image, which is characterized as optical power. It depends on the radius of curvature of the outer and inner surfaces of the lens and the refractive index of the material used.
How to determine the radius of curvature
It is selected individually in each case. The ophthalmologist uses autorefractometry to individually and more tightly fix the lens on the surface of the eyeball. Based on the results obtained, the ophthalmologist can determine the need to use certain models.
Did you know: Having an identical radius of curvature, contact lenses from different manufacturers have different degrees of fit on the eyeball.
Therefore, it is not enough to know only your curvature index when purchasing contact lenses. When purchasing from optics stores, you must also indicate the manufacturer whose products you have worn recently.
Radius of Curvature Table
| Keratoconus stage | Central radius of the cornea, mm | R0, mm | R0-R1, mm | R2-R1, mm | Optical zone diameter, mm | CL diameter, mm | Width of the peripheral zone, mm |
| 1 | 7,2 – 7,0 | 7,25 – 7,0 | 0,5 – 0,8 | 0,8 – 1,2 | 4,5 – 7,0 | 9,2 – 9,5 | 0,7 – 1,2 |
| 2 | 7,0 –6,75 | 7,1 – 6,75 0,5 – 0,7 | 0,7– 1,2 | 4,5 – 7,0 | 9,2 – 9,5 | 0,7 – 1,2 | |
| 3 | 6,7 – 6,0 | 6,8 – 6,0 | 0,4– 0,6 | 0,7 –1,2 | 4,5 – 7,0 | 9,2 – 9,5 | 0,7 – 1,2 |
| 4 | 6,0 – 5,0 | 6,1 – 5,0 | 0,4– 0,6 | 0,6 – 1,2 | 4,5 – 7,0 | 9,2 – 9,5 | 0,7 – 1,2 |
Where R0 — radius of the optical zone, R1 — radius of the sliding zone, R2 — radius of peripheral curvature.
Individual selection of the radius of curvature is determined by the doctor
It is worth understanding that there are numerical expressions for the curvature parameter that are used most often. But even among ophthalmologists there is no such thing as a standard size.
The size and radius of the main apple are completely individual for each person, so the correct selection of contact lenses is carried out strictly according to individual parameters.
It is worth noting that the most popular products with indicators from 8,3 before 8,8 They are sold in optics stores all the time, but deviations, both upward and downward, may require an individual order.
The influence of the radius of curvature on vision
Incorrectly selected lenses can contribute to the development of discomfort during prolonged wear, unclear display of the contour of surrounding objects and the development of diseases. An overly tight fixation on the surface of the eyeball almost completely blocks the access of oxygen to the cornea of the eye.
In addition, the exchange and drainage of tears in the space between the cornea and the contact lens is significantly disrupted. This situation is dangerous because the impaired metabolism does not manifest itself in any way until a critical situation arises due to the fact that the cornea of the eye does not have pain receptors, which leads to corneal hypoxia.
To prevent such a case, it is recommended to use special lenses based on silicone and hydrogel, where silicone is responsible for the access of air to the cornea of the eye directly from the atmosphere, and the hydrogel is responsible for the compatibility of the structure of the lens and the tissues of the eyeball.
Otherwise, installing lenses with an incorrect radius of curvature in a larger direction will lead to a situation where the product on the surface of the eyeball will not be sufficiently fixed.
This causes it to shift when blinking and cause severe irritation. With such incorrect selection, patients often complain of small grains of dust or sand getting into the space between the cornea and the lens, which contribute to severe irritation.
Of course, for a high-quality selection of contact lenses, knowing your radius of curvature is simply necessary.However, a clear understanding is required that only a professional specialist can select the most correct choice.
