Have you been using contact lenses for a long time or are you going to wear them soon? Then you might want to know what the optical specialist must define for choosing the most suitable lenses for your eyes. When issuing a prescription, it is necessary to specify the parameters of the contact lenses on the basis of which the optimal lenses are subsequently selected. Since each person has different eyes, it is important to ensure a comfortable fit.
The basic parameters of contact lenses include:
- The curvature or baseline curve indicates the steepness or evenness of the contact lenses. This should be equal to the curvature of the cornea of the eye, as determined by an ophthalmologist using a slit lamp measurement. Most often the value is between 8.0 and 9.0. The lens box is labeled BC (Base Curve).
- Diameter determines which part of the cornea the lens covers. Specifies the width of the lens from one edge to the other. Most standard contact lenses are produced today on average between 13.5 and 14.5 mm. On the package you will find this information next to the abbreviation DIA.
- The power of the lens or number of diopters determines the ability of the eye to refract rays of light. This is the inverse of the focal length. This can be explained simply by the fact that a lens with a focal length of 1 meter has an optical power of 1 dioptres. The more diopters you need, the worse your vision is. A number with the number of diopters is preceded by a plus (+) or minus (-) sign. A minus sign indicates that it is nearsightedness or poor vision at a distance. Plus, it means that the lenses correct long-sightedness, ie poor vision at close range.
These three basic parameters of the contact lenses are sufficient to provide spherical contact lenses having the same power across the optical portion of the lens. However, if your eye condition is more complicated and you suffer from astigmatism or presbyopia, for example, additional lens parameters should be specified. Toric contact lenses for astigmatism have different strengths in different lens meridians. Presbyopia multifocal lenses consist of different zones for correcting near and far vision.
Additional parameters of toric contact lenses:
- The axis , indicating the rotation angle of the eye curve. It is measured in degrees. It is labeled as AXIS on the packaging.
- Cylinder or cylinder. Lenses for astigmatism have a minus sign before the value.
An additional parameter of multifocal contact lenses is:
- Addition (Abbreviation ADD) - Diopters indicate the value needed to correct distant vision at a distance, and the addition determines the value of the proximity allowance.
If you are just getting started with contact lenses, you may have to try several types at the beginning to find the ideal lenses with the parameters that suit you best. This is always assisted by an eye specialist who can provide a sample of lenses for testing. After the agreed time, you will return to his office to assess whether it has been comfortable to wear the suggested type of lenses and whether you will start to take it regularly.
It should also be noted that the parameters of the contact lenses may change over time. Contact lenses may be changed by the attending physician based on findings during regular checkups, or if you experience discomfort or poor vision.
The article is based on scientific publications.