Understanding your glasses prescription

A glasses prescription receipt can tell you a lot about your eyesight. But often the information can be difficult to understand if you are not used to the technical terms.

OD og OS

OD and OS are abbreviations for oculus dexter and oculus sinister, which are Latin terms for the right eye and the left eye.
Next to each of the two abbreviations is a number. If the number is positive (plus), it means that you are far-sighted and are least-challenged in terms of seeing things far away. If the number is negative (minus), you are short-sighted and are least-challenged seeing things up close. The higher the numbers are for the right and left eye, the higher the strength required in the glasses/contact lenses.

CYL (cylinder) 

CYL is an abbreviation for cylinder, which tells you whether or not you have astigmatism in one or both of your eyes. If there isn’t a number then this means you do not have astigmatism. The larger the number, the greater the astigmatism.

It may sound slightly serious to find out that you have astigmatism in one of your eyes. But this simply means that there is a slight imperfection in the curvature of the cornea. Astigmatisms are corrected by the lenses of the glasses.

If you have astigmatism, the direction of the curvature will be indicated using the term Axe. This will tell you which direction the defect is in. This is measured in degrees. The number given indicates the severity of the astigmatism. The number is between 0-180, where 90 corresponds to the vertical meridian and 180 is the horizontal meridian. This number tells the angle that is required for the lenses to be in order to take correct the astigmatism.

ADD (Addition)

Here you can find extra information about other types of corrections; for example, if you need multi-strength lenses or a reading lenses. The number tells you about the required strength in order to achieve the optimal correction.

PD (Pupil distance)

This is the distance between your pupils (in millimetres).

Visual strength vs. visual acuity

The glasses prescription receipt will mention the visual strength, which importantly should not be confused with visual acuity. These are two different concepts. Read about the different on the page: ‘Difference between visual strength and visual acuity’.