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.
Example of a glasses prescription:
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 right eye and left eye.
+ – This represents where the light reaches in the eye. A plus sign signifies far/long sighted (hyperopia) 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 sighted sighted (myopia) 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)
Cylinder (CYL) – This looks at the shape of the eye to determine whether there is an astigmatism present. If the eye is more rugby ball shaped than football than an astigmatism will be present. This figure determines how much of an astigmatism there is present and can have either a + or – sign in front of the number (if it is not 0).
Axis – This examines where there is a difference in the curvature of the cornea and determines the orientation of the astigmatism. It is quantified between 0 and 180 degrees
ADD – This is for those that have presbyopia and are wearing reading glasses. It is used to determine the additional magnification required for near vision and is always represented as a plus sign.
Prism – Some prescriptions include a prism, this is indicative that there are alignment issues with one or both eyes. The figure used represents the amount of prismatic power required to compensate for this issue to help prevent headaches and double vision.
Base – This is the location of where the prism should be placed in the lens.
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