What Does Your Contact Lens Prescription Mean?
Ever wondered what your contact lens prescription actually means or how to read it? Fortunately, we’re here to help.
Dr. Edwin Wallington, OD, breaks down what a contact lens prescription means and how to understand your own contact lens prescription.
Why Do I Need to Know How to Read My Prescription?
First things first, it can help to understand the function of your contacts and the specific needs of your eyes.
A contact lens has to fit nicely onto the cornea while still allowing the tear layer to perform its job. This is all part of determining your unique contact lens prescription.
There are several factors that go into deciding the correct prescription for each individual. In fact, many individuals even have different specifications for each eye!
Working with your eye doctor to determine and provide your valid prescription is an important step in getting contact lenses.
Contact Prescription Abbreviations and Terms
There are many different measurements that make up a contact prescription. Certain specialized types like contacts for astigmatism, for example, may have additional measurements.
We’ll go over some of the standard measurements that you’ll find on all valid prescriptions.
Base Curve (BC)
The first part of a contact lens prescription is the base curve. Base curve is an indicator of the steepness of the contact lens.
It is a metric to guide fitting the lens curve based on the shape of your cornea.
- If your cornea is flatter, your doctor will reach for a higher numbered base curve.
- If your cornea is steeper, your prescription will have a lower base curve number.
Imagine two bowls side by side. They’re the same width around, but one is taller than the other. The taller one would have a steeper slope from the bottom to the opening. Well, that is exactly what the base curve is.
Next up is the diameter size of the contact lens. An appropriately fit base curve has to be just a little loose so the cornea isn’t squeezed too tight.
The contact lens diameter helps stabilize this soft fit to allow the contact lens to sit comfortably on the dome of the cornea and allow for tear movement.
The style of the contact lens consists of individual materials, water content, and oxygen transmissibility along with other agents and curves to enhance the design.
The style is what usually “makes or breaks” a contact lens fit.
Base curve is objectively determined, diameter is almost always predetermined, but style is subjective. Since different people have different natures to their eyes, each individual may prefer a different style of contact lenses.
The power is a measurement used to determine the prescription strength for contact lenses. Power measurements can be either positive or negative, depending on the direction that the light’s focal point needs to move to focus for your eyes.
The basic sphere power measurement is what you’ll find most commonly in prescriptions, however, there are other power measurements that may be found on more specialized prescription types.
These power values are determined by where the power number sits within the overall range and is based on how much assistance our eyes need to focus.
What Does a Contact Lens Prescription Look Like?
A contact lens prescription is only considered valid if it meets the many criteria set forth by the FDA. These include:
- Patient name
- Exam date
- Expiration date
- Full prescriber information
- Manufacturer and brand information
- Base curve
Other details such as cylinder power, axis,and add power are also details that are necessary only if the listed brand requires it.
Go to a licensed eyecare provider to receive an eye exam to get a valid prescription, such as an optometrist or an ophthalmologist.
How to Read a Contact Lens Prescription on the Box
The details on a contacts box for your specific prescription should have all of the same information that was mentioned above. Those are all of the essential pieces to a valid prescription.
It’s also important to note that contacts and glasses prescriptions are not always the same. A contacts prescription should be seen as unique from other vision prescriptions.
Eyeglass power prescriptions are not the same as contact lens prescriptions. Besides all of the fitting details such as base curve and diameter of the contact lens, a contact lens power usually does not convert directly from a glasses power.
Types of Contact Prescriptions
As mentioned above, there are some aspects of a prescription that all prescriptions will contain, as they are required by the FDA. However, there are different types of contacts that will contain additional information to ensure the prescription is accurate and complete.
Every contact lens box will have the:
- Base Curve
Example: Acuvue Oasys 8.4 /-2.50/14.0
Other Brands may require additional power information. An example of this would be a contact lens for astigmatism (also known as a TORIC lens), which must also include:
- Cylinder Power
- Axis (ex: 180).
Example: Acuvue Oasys for Astigmatism 8.6/-2.50-1.25X180/14.5
Another power that may need to be identified in a contact lens prescription is ADD power, typically for people over forty with presbyopia or in need of a multifocal
Example: Acuvue Oasys Multifocal 8.4/-2.50/14.3 MED (Medium ADD power = MED).
The Deliver Contacts Viewpoint
Deliver Contacts is in the business of selling top brand contact lenses at the best prices on the internet with free delivery, but not at the expense of our customers’ eye health.
The industry of eye health care is currently being tested and pushed to limit the standards on contact lenses. Deliver Contacts affirms that contacts should continue to be fit by licensed professionals and supports the stance of the American Optometric Association (AOA) and their own Michigan Optometric Association (MOA) in their continued leadership to protect the ocular health of the American people.
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