Are eyeglasses and contact lenses prescribed the same? Unraveling the mystery of the vision correction puzzle
Have you ever wondered if your prescriptions for glasses and contact lenses are the same? If you are someone who regularly switches between the two and has carefully examined these prescription lists, you may have noticed some differences. This blog post will help you understand why these prescriptions are different and what this means for your vision correction.

Clearing the Fog
First, let's make sure that the prescriptions for glasses and contact lenses are not the same. While both are used to correct your vision, there are key differences in the measurements and values that determine how your eyes are corrected.

Anatomy of the Eye: A Quick Primer
The cornea, the clear front surface of the eye, and the eye's lens work together to focus light onto the retina, the light-sensitive tissue at the back of the eye. When the cornea and lens cannot fully focus light, you develop refractive errors such as myopia (nearsightedness), hyperopia (farsightedness) and astigmatism.

Eyeglasses vs. contact lenses: why the difference?
The main reason for the prescription difference is the distance between the corrective lenses and your eyes. Eyeglasses are placed about 12 mm from your eye, while contact lenses are placed directly on the surface of the cornea. This difference in distance affects the way light is refracted and focused on the retina, resulting in different measurements of vision correction.

Decoding prescriptions: What do the numbers mean?
The following is a breakdown of common values in eyeglass and contact lens prescriptions:

Sphere (SPH): This value represents the number of lens diopters needed to correct nearsightedness or farsightedness. It is usually measured in diopters and is usually the same for both eyeglasses and contact lenses.

Cylindrical (CYL) and Axial (AX): These values correct astigmatism, irregular curvature of the cornea or lens. While the CYL values may be similar in both prescriptions, the axis values may differ depending on the distance between the lens and the eye.

Base arc (BC): Specific to contact lens prescriptions, BC indicates the curvature of the contact lens to ensure a proper fit to your cornea. This value does not apply to eyeglasses.

Diameter (DIA): Another contact lens specific value, DIA indicates the overall size of the contact lens to fit comfortably in your eye.

Additive Degrees (ADD): Commonly found in prescriptions for bifocal, progressive or multifocal lenses, ADD indicates the number of additional degrees of near vision required. This value may vary by eyeglass and contact lens prescription.

What does this mean for you?
As you can see, there are important differences between eyeglass and contact lens prescriptions that affect vision correction. It is important to obtain separate prescriptions for eyeglasses and contact lenses during your eye exam. Using the wrong prescription can lead to discomfort, headaches and inadequate vision correction.

Remember, your eyes are unique and your vision correction should be tailored to your specific needs. If you have any questions or concerns, please consult your eye care professional to ensure you are getting the best care for your eyes.