Why Contact Lens Prescriptions Are Different from Glasses Prescriptions

If you use both eyeglasses and contact lenses, you might wonder why the prescriptions for each are different. Here's a simple explanation.

Eyeglasses vs. Contact Lenses

Eyeglasses Prescription:

  • Sphere (SPH): Corrects nearsightedness or farsightedness.
  • Cylinder (CYL) and Axis: Correct astigmatism.
  • Add: For reading lenses, like bifocals.

Contact Lens Prescription:

  • Includes Sphere, Cylinder, and Axis, but adjusted for contacts.
  • Adds Base Curve (BC): The curvature of the lens to fit your eye.
  • Includes Diameter (DIA): The size of the lens.
  • Specifies Lens Brand and Material: Ensures comfort and eye health.
  • Details Replacement and Wear Schedule: How often to replace and how long to wear.

Key Differences

  1. Fit and Comfort: Contacts sit directly on your eye, so they need to fit the shape of your cornea perfectly. Glasses don't have this requirement because they sit away from your eyes.
  2. Lens Material and Type: Contacts come in various materials, each suited to different eyes. The prescription specifies the best material for you.
  3. Base Curve and Diameter: Contacts need to match your eye's curvature and size for comfort and effectiveness.
  4. Power Adjustments: Contacts might need slightly different power adjustments compared to glasses since they sit directly on your eye.
  5. Eye Health: Contacts require specific details to ensure they don't harm your eyes, considering factors like dryness or allergies.


Glasses and contact lenses serve the same purpose but require different prescriptions due to how they interact with your eyes. Always consult with your eye care professional to get the right prescriptions and ensure the best vision and eye health.