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What Do the Numbers on My Prescription Mean?

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by Dr. Rachel Ng OD

As you leave your annual eye appointment, a prescription is granted if you benefit from wearing glasses. Many children and adults require refractive correction either for full time wear or part time wear to enhance their vision and prevent eyestrain.

As you walk towards the gallery to be personally fit with a frame by a stylist, you may wonder what the numbers on the glasses prescription mean.

The first number on the script is what is called the sphere power.

It will be positive for a farsighted person, or it may be negative for a person who is nearsighted. The unit of this number is called a diopter which indicates the power of the prescription. A higher number would indicate a stronger prescription.

The second number of the script is called the cylinder power.

This indicates the amount of astigmatism in the prescription. Astigmatism is common and easily corrected with glasses or contact lenses. It occurs when the eye is not completely round but more oval in shape. Those with astigmatism may notice more glare and haloes if no corrective lenses are worn.

The third number following indicates the direction of the cylinder.

This is measured in degrees therefore this number will always fall between 1 and 180. This determines the direction of the astigmatism. Most eyes are symmetrical and will have similar astigmatism axes however it is not always the case.

When a frame stylist examines your prescription, they will recommend specific frames styles to suit your prescription and visual needs. For example, a high minus sphere for high myopia will result in a lens that is thick on the edges and thin in the middle.

A frame stylist may recommend a plastic frame with a thicker edge that will hide the thickness of the lens. Additionally, a frame smaller in size will reduce the thickness of the lens being visible. Not only are your spectacles meant to help you see clearly but also to look your best.

Knowing the individual needs of each wearer is imperative to ensure the highest level of comfort.