If you have ever had a prescription for glasses in your hands, you will have noticed a lot of data with signs that are difficult to understand. Here we are going to clarify each of these details point by point so that you understand well what correction your vision needs.

1.- Sphere (ESF or SPH)

This field specifies the diopters or power required for the lens to correct hyperopia or myopia . If the values ​​appear positive (+) we are talking about hyperopia, while if they appear negative (-) we are talking about myopia. These problems are associated with poor near and far vision respectively, and the higher the value in diopters, the worse the quality of vision without correction.

2.- Cylinder (CYL or CYL)

The cylinder value, if it appears, indicates the diopters needed to correct the astigmatism that occurs when the eye has two different prescriptions due to a non-spherical cornea. This data can be positive (+) or negative (-) depending on whether it is a hyperopic or myopic astigmatism and is accompanied by another data in the form of an axis in sexagesimal degrees , that is, between 0º and 180º, which is where the astigmatism is found.

It is because of this last fact that, even if two people have the same diopters of astigmatism, they do not see well if they exchange their glasses with different axes.

3.- Pupillary Distance

Pupillary distance or PD is, as its name suggests, the distance from the edge of the eye to the pupil, measured in millimeters (mm). Although it is a simple value to measure, it is often not included in the prescription, but it is a good idea to look for this and ask for it, as it will determine the optical center of the prescription lenses.

4.- Addition (ADD)

At this point the information gets a little “mixed” and complicated, but don’t worry, we’ll make it clear. This information is positive diopters , like those of hyperopia, but in this case they are those of presbyopia or tired eyes and they should never be confused because they are not the same.

The addition indicates the diopters that are added to those of myopia or hyperopia to see correctly up close when there is tired eyes. It is used when buying reading glasses or when bifocal or multifocal lenses are going to be used.

As a curiosity , a myopic person of -2 with an addition of +2 only has to take off his distance glasses to see well up close, because myopia compensates for the tired eyes. You can learn more about this in this article .

5.- Visual Acuity (VA)

This measurement is not used much in medical prescriptions in Chile because it is not used by opticians to make lenses, however, it is the most important because it speaks of the quality of vision with respect to what is considered statistically “normal.”

Visual acuity values ​​can be expressed as a percentage (120%, 100%, 50%…) or as a decimal (1.2, 1.0, 0.5…). Normal vision is one that reaches a value of 100% or 1.0. There is a scale that is common in English-speaking countries (the 1.2 scale). Snellen ) where VA is shown as a fraction. A VA of 20/20 would correspond to 100%.

Visual acuity is measured without correction (VAsc) to assess the quality of our vision without glasses and with correction (VAcc) to see the improvement we obtain with optical correction.

EXAMPLES OF OPTICAL EYEGLASSES PRESCRIPTIONS