Understanding Your Contact Lens Prescription

A contact lens prescription is essential for ensuring that lenses fit well, correct vision properly, and maintain eye health. Here, we’ll walk through the different parts of a contact lens prescription so you can feel confident ordering lenses and understanding what each part means

1. Contact Lens Rx

The abbreviation "Rx" simply stands for "prescription." It’s crucial to confirm that the prescription specifically states it is for contact lenses, as prescriptions for glasses are different. Contact lens prescriptions take into account that lenses sit directly on the eye, unlike glasses lenses, which are positioned slightly away from the eye. Using a glasses prescription to buy contact lenses can result in improper fit and incorrect vision correction.

2. Expiry Date

Most contact lens prescriptions are valid for 12 months. The expiration date encourages regular eye exams to ensure that your eyes remain healthy, especially since your vision and eye shape can change over time. Eye care professionals also use regular visits to check for any complications related to contact lens wear, such as dryness or corneal health issues, which ensures that you’re using the most suitable lens product.

3. Base Curve (BC) & Diameter (DIA)

The Base Curve (BC) refers to the curvature of the back surface of the contact lens. This curvature needs to match your cornea’s shape to ensure a secure and comfortable fit. The Diameter (DIA) is the size of the lens from one edge to the other, measured in millimeters. Both of these measurements are critical for proper fit and comfort. After a contact lens fitting, your optometrist will determine the right BC and DIA based on your cornea’s shape and size.

4. Sphere, Cylinder, and Axis

These three values are essential for correcting vision, particularly for people with astigmatism. Sphere (SPH): The Sphere, or power, corrects nearsightedness or farsightedness. This value is written in diopters (D) and may include a plus (+) or minus (-) sign, depending on your specific needs. Cylinder (CYL): The Cylinder value indicates astigmatism correction. Astigmatism is caused by an irregular curvature of the cornea, and the CYL power corrects this by balancing the uneven shape. Axis: The Axis is the angle at which the cylindrical correction should be placed to properly address the irregular shape of the cornea. This value ranges from 0 to 180 degrees and is only present if the prescription includes a CYL value.

5. Multifocal Variables (Add, DNHL, Mono D/N)

These additional variables are specific to multifocal or bifocal contact lenses, which are designed for people who need help with both near and distance vision, usually due to presbyopia. Add: This refers to the additional power needed to assist with close-up vision, usually marked as “High” or “Low” based on the amount of correction required. DNHL or Distance/Near: Some brands use DNHL to mark lenses for distance or near use in one eye as part of a monovision system. Your optometrist will determine the best configuration. Mono D/N: Monovision involves using one eye for distance (D) and the other for near vision (N). This type of design can be useful if you need both distance and reading support but prefer a monofocal lens.

6. Contact Lens Brand and Type

Unlike glasses, contact lenses are brand-specific. A valid contact lens prescription specifies a particular brand and type, as different brands may have variations in lens material, water content, and curvature. This customization ensures the best fit, vision clarity, and comfort for your eyes. If you wish to change brands or try a different type of lens, a new prescription from your optometrist is required.

Ordering Your Contact Lenses with Confidence

Knowing these details can make ordering contact lenses easier and more straightforward. Keep in mind: Always use a valid, up-to-date prescription, and double-check that it specifies contact lenses, not glasses. Consult with your optometrist if you’re interested in switching brands or types of lenses, as new measurements may be necessary. Stay current with eye exams, as they’re essential to maintaining eye health and ensuring that your prescription continues to be effective. With an accurate understanding of these prescription elements, you’ll be better prepared to order your contact lenses confidently and enjoy the best possible vision and comfort.