How To Read Glasses Prescription For Contacts
This article will help you understand your new contact lens prescription after you have completed your contact lens fitting and received your prescription.
Where can I find my prescription?
In most cases, the details of the contact lenses you should wear can be found on the following documents:
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The prescription for contact lenses that your optician has provided to you;
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You can find this information on the box side of your contact lenses
It is also possible to contact your optician to find out the details of your lenses if you are unable to locate your prescription.
A copy of your prescription will be given to you at your local optician when you have a contact lens fitting or check-up. This is usually contained on a form such as the one below.
The proper way to read your contact lens prescription
Typically, a prescription for contact lenses consists of the following elements:
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A Basecurve (BC): is a number that describes the curvature of your contact lens. This number is used by your optician to determine the best fitting contact lens for you. For example, a BC of 8.5 denotes a contact lens with a curvature that matches the curvature of your eye.
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Diameter: Diameter measures the distance between one edge of the contact lens and the other. It is used to determine what parts of your eye the contact lens will cover.
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A power (pwr) / sphere (sph) / dioptre (D) value: indicates how much power your lens must have to correct your long or shortsightedness and is expressed in Dioptres. When the number is greater, your prescription is stronger. Consequently, a minus (-) sign indicates you are short-sighted, while a plus (+) sign indicates you are long-sighted.
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Contact lens name: Most contact lens prescriptions will have a brand, type, and manufacturer name, allowing for the possibility of reordering your lenses if the prescription is still valid. For example, 1 Day Acuvue Moist. ACUVUE, CooperVision, Ciba Vision / Alcon, and Bausch and Lomb are the main manufacturers that you will come across.
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Cylinder: refers to how much astigmatism you have, determined by the curvature of the structures in your eye. If this section is empty, you are simply longsighted or shortsighted. If you do have astigmatism, a value will be entered here, along with an axis. For example, left eye: -2.25; right eye: -2.25.
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Astigmatism axis: Measured in degrees, this value is normally between 0-180 and indicates the direction in which power is added to the contact lens to correct astigmatism. Examples are 10, 19, and 29.
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Additional power: value is any extra magnification provided by a multifocal contact lens to assist with reading and close work. This can be recorded as a High, Low, Medium or the power value rather than a + value.
Are contact lens prescriptions and glasses prescriptions the same?
There is a difference between a prescription for contact lenses and a prescription for glasses
If you are ordering contact lenses, you should know the difference between a glasses prescription and a contact lens prescription. It’s very common for glasses prescriptions to be confused with contact lens prescriptions.
Contact lenses cannot be purchased from a glasses prescription since they sit on the surface of the eye while spectacle lenses are positioned slightly farther away. This difference in position determines how powerful the lens will be.
It is important to note that the sphere, cylinder, and axis values in your glasses prescription must be adjusted by your optician to achieve the same power in your contact lens. Your optician is the only one who can calculate this for you.
The prescription for spectacles will not contain the following information:
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Base curve;
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Diameter;
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Name and manufacturer of contact lenses.
In most cases, contact lens prescriptions will not have an axis value other than steps of 5 or 10 degrees.
