If you have ever had a recipe for the prescription of glasses in your hands, you will have observed a lot of data with signs that are difficult to understand. Here we will clarify point by point each of these data so you understand well what correction your vision needs.
1.- Sphere (ESF or SPH)
This field specifies the diopters o necessary power of the lens to correct the farsightedness or myopia. If the values appear in positive (+) we are talking about a hyperopia whereas if they appear negative (-) we are in front of a myopia. These problems are associated with poor near and far vision respectively and the higher the value in diopters, the worse the quality of the vision without correction.
2.- Cylinder (CIL or CYL)
The value of the cylinder, if it appears, indicates the diopters necessary to correct the astigmatism which occurs when the eye has two different graduations due to a non-spherical cornea. This data can be positive (+) or negative (-) depending on whether it is a hypermetropic or myopic astigmatism and is accompanied by other data in the form of an axis in sexagesimal degreesIe Between 0º and 180º which is where astigmatism is.
It is by this last fact that, although two people have the same astigmatism diopters, they do not see well if they exchange their glasses having different axes.
3.- Distance Pupilar
The pupillary distance or DP is, as the name suggests, the distance from the edge of the eye to the pupil, measurement in millimeters (mm). While it is a simple value to measure many times they do not put it in the recipe, it is good to look at this and ask for it, since it will determine the optical center of the prescription glasses.
4.- Addition (ADD)
At this point the information is "mixed" a little and it gets complicated but do not worry, let's make it clear. This data is positive diopters, like those of hyperopia, but in this case are those of the presbyopia o tired eyesight and they should never be confused because they are not the same.
The addition indicates the diopters that are added to those of nearsightedness or farsightedness to see properly up close when there is tired eyesight. It is used when you are going to buy glasses close up or when you are going to use bifocal or multifocal glasses.
How curiosity, a myopic of -2 with an addition of + 2 you only have to remove the glasses from far to see closely because the myopia compensates the tired sight. You can know more about it in this article.
5.- Visual acuity (AV)
This measure is not used much in medical prescriptions in Chile because it is not used by lenses to make crystals, however, it is the most important because it speaks of the quality of vision with respect to what is considered "normal" statistically.
The values of visual acuity can be reflected in the form of porcentaje (120%, 100%, 50% ...) or in form decimal (1.2, 1.0, 0.5 ...). A normal vision is one that reaches the value of 100% or 1.0. There is a frequent scale in Anglo-Saxon countries (scale of Snellen) where the VA is shown as a fraction. An 20 / 20 AV would correspond to 100%.
Visual acuity is measured without correction (AVsc) to assess the quality of our vision without glasses and with correction (AVcc) to see the improvement we get with optical correction.