LET'S LEARN ABOUT OPTICAL CORRECTIONS AND RECIPES
When the ophthalmologist or optician graduates our vision and sees that we need optical correction, they generally write us a prescription for glasses or contact lenses that we must take to the optician when we go to buy them. But it is not easy to understand what he puts in it. With this little guide you will be able to correctly read and interpret the prescription for your optical glasses.
THE PRESCRIPTION OF EYEGLASSES AND OPTICAL FRAMES GENERALLY CONTAINS CRIPTIC VALUES AND UNINTELLIGIBLE TO THOSE WITH NO OPTICAL KNOWLEDGE.
In most cases, the patient does not understand the values, symbols and abbreviations that appear in the vision graduation prescription delivered by professionals. With this brief guide and through practical examples we want to shed some light and help you understand what we are dealing with.
The values shown on your glasses prescription are also those of your vision prescription. That is, the optical correction that your eyes need to have the clearest vision possible and achieve the highest visual acuity.
FREQUENT ABBREVIATIONS IN THE RECIPE
RE : Right eye
LE : Left Eye
AO : Both eyes
AD : addition
ESF : Sphere
CYL : Cylinder
VA : Visual acuity
VL : Far / distant vision
VC/VP : Near / near vision
VI : intermediate vision
PD : Pupillary Distance
If you have ever held a prescription for glasses in your hands, you will have observed a lot of data with signs that are difficult to understand. Here we are going to clarify each of these data point by point so that you understand well what correction your eyesight needs.
1.- Sphere (ESF or SPH)
This field specifies the diopters or power required of the lens to correct for farsightedness or nearsightedness . If the values appear positive (+) we are talking about hyperopia while if they appear negative (-) we are facing myopia. These problems are associated with poor near and far vision, respectively, and the higher the value in diopters, the worse the quality of uncorrected vision.
2.- Cylinder (CIL or CYL)
The cylinder value, if displayed, indicates the diopters needed to correct for 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 Find the astigmatism.
It is because of this last fact that, even if two people have the same astigmatism diopters, they do not see well if they exchange their glasses having different axes.
3.- Pupillary Distance
The 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, many times they do not put it in the prescription, it is good to look at this and ask for it, since it will determine the optical center of the medical prescription lenses.
4.- Addition (ADD)
At this point the information is "mixed" a bit and it gets complicated but don't worry, we are going to make it clear. This information is positive diopters , like those of farsightedness, but in this case they are those of presbyopia or 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 myopia or hyperopia to see correctly up close when there is tired eyesight. It is used when buying close-up glasses or when bifocal or multifocal lenses are going to be used.
As a curiosity , a nearsighted person of -2 with an addition of +2 only has to remove his glasses from a distance to see well up close, since myopia compensates for tired eyesight. You can know more about it in this article .
5.- Visual Acuity (VA)
This measure is not used much in medical prescriptions in Chile since it is not used by opticians to make glasses, however it is the most important because it speaks of the quality of vision with respect to what is statistically considered "normal".
The visual acuity values can be reflected as a percentage (120%, 100%, 50%...) or as a 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 AV is shown as a fraction. An AV of 20/20 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 obtain with optical correction.
Below we present a series of examples of the different prescriptions for glasses that we can find.
Example of a prescription for a myopic person:
RE : -2.75 LE : -1.25
Example of a prescription for a hyperopic person:
RE : +1.25 LE : +2.00
Example of a prescription for a person with myopia and astigmatism :
OD : -3.25 (-0.75) 110º LE : -2.25 (-1.25) 90º
This same graduation can be expressed in an equivalent way with positive cylinder values by applying a transposition rule.
RE : -4.00 (+0.75) 20º LE : -3.50 (+1.25) 180º
Example of prescription for a person with farsightedness , astigmatism and presbyopia :
RE : +2.00 (-0.5) 80º Ad +2.00 LE : +1.50 (-1.00) 45º Ad +2.25
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