Is Contact Lens Prescription the Same as Glasses?
Throughout this article, we will answer the question “is contact lens prescription the same as glasses?” and explore the two different prescriptions. Understandably, many people assume that their two prescriptions are the same, but is this the case?
The answer is no! Your contact lens prescription and glasses prescription is not the same. Since glasses rest slightly in front of your eyes and contact lenses sit directly on them, you need two separate tests to determine their unique measurements.
How is contact lens prescription different from glasses?
The two differ because contact lens prescriptions include certain specifications that are not part of a glasses prescription. If you would like the option of wearing both contact lenses and glasses, then you need to know both individual prescriptions.
The main factor that sets your contact lens prescription apart is that it contains added specifications that do not apply to glasses, such as base curve and diameter. With this key difference in mind, let’s discover the basics to read both prescriptions.
How to read contact lens prescription
Some of the specifications you find in your contact lens prescription will seem unfamiliar if you have only worn glasses. However, all of the numbers and letters have a unique purpose.
Not sure where to find this information? You can often see your contact prescription on the end or side of the box, as well as on the blister packs. Here’s what everything means:
• Diameter (DIA): This parameter determines the contact width you need for your eyes. It is represented in millimetres.
• Base curve (BC): Also usually written in millimetres, BC outlines what curvature matches your eyes
• Sphere/Power (SPH/PWR): Sphere or power is used to establish whether you are long-sighted (hyperopia) or short-sighted (myopia). The ( + ) symbol is used for hyperopia, while the ( - ) symbol is used for myopia.
• Cylinder (CYL): This figure shows the extra corrective power needed for your astigmatism. It is represented as a plus or minus along with a negative value that is a multiple of 0.25.
• Axis (AX): This figure corrects the abnormal curvature of the eye caused by astigmatism. It decides the angle of correction needed and is between 0 - 180 degrees.
Contact lens prescriptions for presbyopia will contain the following:
• Addition (ADD): Represented as a number between 0.50 and 3.00 or as low, medium, or high, this figure shows what level of correction you need to have clear vision at a close distance.
• Dominant (D/N): The dominant or non-dominant eye is marked on prescriptions for multifocal or bifocal lenses with a “D” / “N” or “OD” / “OS”.
How to read glasses prescription
When you compare the above figures to your glasses prescription, you will notice the differences. Here is how you can make sense of your glasses prescription:
• Sphere (SPH): ( +) or ( - ) determines if you are long or short-sighted and the number that follows is the power of correction.
• Addition (ADD): This represents the correction needed for close distance for activities such as reading.
• Cylinder (CYL): This number refers to how much correction your astigmatism needs. If this is blank, it does not require correction.
• AXIS (AX): This indicates the position/angle of the cylinder and is between 0 and 180 degrees.
• Pupillary distance (PD): This figure indicates the distance between your pupils. Use our pupillary distance tool if you need to find it out.
• Prism: When someone suffers from muscle imbalances in their eyes, prism correction aligns double vision (diplopia).
• Base: Different to base curve for contacts, base shows the direction of the prism needed in your lenses and is usually represented as IN, OUT, UP, or DOWN.
As you can see, not all of the figures on your contact lens and glasses prescription will match. . Understanding the difference is essential to avoid wearing the incorrect prescription which can lead to eye issues such as blurry vision. Now that you know the difference, you should be good to go!