Your ophthalmologist gave you a prescription, but how do you read it properly? Between acronyms, numbers and hidden meaning, here is how to decode it.

Medical prescriptions are often complex to read, whether on the name of the drugs, or on the traditional cliché of the doctor’s handwriting … Those in ophthalmology are in this respect even more specific, and useacronyms unique to the profession.

On the prescription given to you by the doctor and to be sent to the optician, for example, there are several abbreviations.

• FROM : for Eye Dking
• AND: for G eyeeft
• ODG: for Eye Dking and Geft
• VP: for Vision de Pvery
• VL : for the Vision de Loin
• WE : for Vision Iintermediate
• SPH : designates the term Sphere
• ADD : designates the term Addition
• AV: denotes the term ofVisual acuity
• CYL : designates the term Cylinder

So far, everything is fine, and you might have even deduced these codes on your own. Alas, the ordinance is linked with other figures, without link between them.

For example, you can read:

OG -2,10 (-0,50) 90 °

OD -0,50 (-0,50) 150 °

Each line corresponds to the vision of one eye, OG for the left, OD for the right.

The first digit corresponds to the default of focal distance, also called the Sphere, that is, the place where the light rays cross in relation to the retina. Ideally in one eye Emmetropic (without defect), this figure would be zero (it is sometimes written (+ -) 0,00 when an eye is emmetropic). Here it is expressed in diopters, the corrective power recommended for optical glass.

Negative number: sign of myopia

If the number is preceded by a ‘-‘ sign, it means that the focal length is in front of the retina, and therefore that the patient is myopic. Here, the left eye is more myopic than the right eye, and the correction to be made will be all the more important. The person therefore sees blurry from afar, but well up close.

Positive number: sign of hyperopia

If, on the contrary, the figure is preceded by a ‘+’ sign, this time the focal length is behind the retina, and therefore the person studied is hyperopic. The person therefore sees blurry up close, but correctly in the distance.

Figures in brackets: astigmatism

The numbers in parentheses quantify theAstigmatism, it is the Cylinder, the shift between the images due to a deformation of the cornea. The figure which follows them is expressed in degrees (here 90 and 170 °), it is theAxe, or the angle of orientation of astigmatism. Vision will be blurry both near and far.

Numbers after the acronym “Add”: presbyopia

Sometimes, and especially with age after 45 years, the prescription is adorned with an “Add”, which means “Addition”. This indicates the correction to be made to treat a presbyopia, in particular for the addition of progressive lenses.

The pupillary distance:

The gap between the two pupils is written in different ways, sometimes with a simple “gap” written on the prescription, or in relation to each eye: OD 33, OG 33,5.

What is a diopter?

The diopter is a physical unit used in optics, more specifically to designate the vergence, the inverse of the image focal length (in meters). It is mainly used to quantify the optical correction to be made to a lens.

For example, if you are nearsighted with a left eye diopter of -2, it means that you are able to see an object 50 cm away “effortlessly”, while a myopic of -4 diopters will see clearly at. ¼ = 25 cm (but more blurry from a distance).

A link also exists between the measurement of visual acuity and the diopter to be applied in correction.

So,

• An emmetropic eye (without defect) will have 0 diopters, that is to say a vision of 10/10
• Low myope of -0,75 diopter equals 5/10 to 7/10 vision
• A low myopia of -1,50 diopters is equivalent to a vision of 2/10 to 4/10
• An average myopia of -2,50 diopters is equivalent to a vision of 1/10
• A strong myopia of -6 diopters is equivalent to a vision less than 1/20

The most attentive may have already noticed it, but the certificates of authenticity provided by the opticians do not present the same figures as those on the prescription. Until sometimes seeing positive numbers instead of negative, or different angles in case of astigmatism.

This difference is normal, it is due to a difference in standard between the optical measurement of the ophthalmologist, based on the human eye, and that of lens manufacturers, linked to their curvature.

An ophthalmic prescription is valid for different durations depending on the age of the patient. Thus it lasts less for the young and the elderly, categories with a rapid evolution of the eye.

It lasts :

• 1 year for children under 16 *
• 5 years for 16 to 42 years old *
• 3 years for people over 42 *

(* For prescriptions after October 17, 2016 and unless the ophthalmologist contraindicates them)