How to Read Your Contact Lens Prescription

If you wear contact lenses regularly, you may already know how to read your contact lens prescription. However, the terms and values on an eye prescription can be confusing for some individuals. So, here in this useful guide, ‘how to read an eye prescription’ is explained in detail so you can understand what each of the values on your contact lens prescription means. Let’s start by understanding how to get an updated contact lens prescription.

• How to get your contact lens prescription
• Contact lens eye prescription explained
• Astigmatism contact lens prescription explained
• Multifocal contact lens prescription explained
• Frequently asked questions

How to get your contact lens prescription

First, you need to have your eyes tested by a certified optometrist. After your eyes are tested, you’ll have a lens-fitting appointment. Once your optician is happy with how your lenses fit, they will issue you a copy of your contact lens prescription. NHS recommends that everyone should have an eye exam at least once every two years, or more often if advised by their optician.

Contact lens eye prescription explained

The three main specifications on a regular contact lens prescription are power, base curve and diameter. However, it must also specify the patient’s name, optician’s name and signature, and the issue and prescription expiry date.

Let’s understand the specifications mentioned on your prescription.

Power/Sphere (PWR/SPH)

Measured in dioptres, power or sphere indicates the level of correction your contact lens must provide to correct your vision. If your prescription shows a minus sign (-), this means that you are short-sighted and have myopia and if your prescription shows a plus sign (+), this means that you are long-sighted and have hyperopia.

Base curve (BC)

The base curve is the curvature of the back surface of the contact lens. This measurement helps ensure the contact lens fits your eye correctly. It relates to the curvature of your cornea and is measured in millimetres (mm). A lower base curve denotes a steeper curve, while a higher base curve indicates a flatter curve.

Diameter (DIA)

The diameter measures the width of your contact lenses from one edge to another and is measured in millimetres. Wearing a lens with the wrong diameter may cause blurry vision and discomfort.

Astigmatism contact lens prescription explained

If a contact lens prescription is for someone with astigmatism who needs toric contact lenses, it will include the Cylinder and Axis value.

Cylinder (CYL)

Cylinder is usually written in minus (-) form and describes the amount of astigmatism. It signifies the extra visual requirements needed in toric lenses to correct astigmatism.

Axis

The axis is measured in degrees (between 1 and 180) and determines the angle of correction needed for the cylinder power. This figure is needed to compensate for the cornea’s non-spherical shape due to astigmatism. Simply put, the axis indicates the orientation of the cylinder power and where it should sit.

Multifocal contact lens prescription explained

If a contact lens prescription is for someone with presbyopia who needs multifocal contact lenses, it will include the ADD field and may also have ‘D’ and ‘N’.

Addition (ADD)

ADD power is usually written in dioptres as a plus (+) value and indicates the power you need to see at a closer distance, such as for reading or performing a close task. It indicates the magnifying power in multifocal contact lenses. This is usually a number between 0.50 and 3.00.

Dominant (D) and Non-dominant (N)

Presbyopia requires correction through multifocal contact lenses that sometimes offer visual correction through a ‘dominant’ and ‘non-dominant eye’. The figures ‘D’ and ‘N’ are used to indicate which is which. Sometimes, this is also referred to as ‘distance’ and ‘near’.

Frequently asked questions

What is the strongest contact lens prescription?

Contact lenses can be prescribed for extreme degrees of myopia or hyperopia, including those who need correction of more than -20 dioptres. Some tailor-made lenses can be available in over -30 dioptres. For regular soft contact lenses, the highest corrective power is usually about -12.00 dioptres. Some monthly soft contact lenses can correct up to +/-20 dioptres sphere, and some toric contact lenses can correct astigmatism up to -5.75 cylinder.

Can I use my glasses prescription for contact lenses?

No, you cannot use your glasses prescription to buy contact lenses because glasses sit slightly further away from your eyes, while contact lenses sit directly on the cornea. For detailed information, you can read our blog on ‘Can you convert a glasses prescription to a contact lens prescription?’

What are the effects of wearing contact lenses with the wrong base curve?

As the base curve determines the right fit of contact lenses, wearing lenses with the wrong base curve can cause irritation, redness, blurry vision, discomfort and potentially damage the cornea.

How to order contact lenses online?

You can order contact lenses online easily from Feel Good Contacts at affordable prices. For more information, refer to this step-by-step guide on ‘How to Order Contact Lenses.’