How to Read a Prescription

When you have an eye exam you are often given a slip of paper containing your prescription. However, most of us do not know how to read this information as we are unfamiliar with the terms and solely rely on what is told to us by our optometrist.

Not all eye prescriptions are the same and there is a significant difference between glasses and contact lenses prescriptions. This is due to the fact that glasses rest approximately 1 to 2 centimetres from your eyes and contact lenses are placed directly on the surface of the eye, and also because contact lenses prescriptions contain information directly related to size and positioning of the lens. Overall, glasses prescriptions are a more accurate account of an individual’s visual conditions, given that glasses are able to accommodate for the correction of more complex conditions than contact lenses.

There are a lot of abbreviations used for medical terms and without knowing what these mean it is very difficult to read a prescription. Below is a list of the most commonly used terms and abbreviations:

• OD and OS – Are abbreviations for Oculus Dexter and Oculus Sinister, which is Latin for the right eye and left eye.
• + – This represents where the light reaches in the eye. A plus sign signifies far/long sighted, which is when the light is focused beyond the retina.
• – – This represents where the light reaches in the eye. A minus sign signifies near/short-sightedness which is when the light is focused in front of the retina.
• D – Dioptre is the unit of measurement to determine the refractive power of the lens
• Sphere (SPH) – This is the amount of lens power required to correctly focus the light to the retina. Can have either a + or – sign in front of the number (if it is not 0)