What’s the Difference Between Glasses and Contact Lens Prescriptions?

July 27th, 2021

Wearing eyeglasses, contacts or both is a personal choice. However, it’s important to understand that both vision correction options have different prescriptions requiring different eye exams. Our eye doctors in Mesa and Chandler have the training to provide you with both prescriptions and help you learn more about the care and use of each option.

At Swagel Wootton Eye Institute, we provide comprehensive care that includes explaining your prescriptions and helping you choose the products you need from our optical center. For glasses that includes the prescription, frames in style. For contact lenses that includes identifying the right brand and style to match your vision needs.

Eyeglasses Rx

Eyeglass prescriptions vary significantly from contact lens prescriptions. However, there are also similarities. For example, eyeglasses use the same abbreviation for right eye and left eye.

  • OS: ocular sinister or left eye
  • OD: ocular dexter or right eye

Sphere (SPH)

This indicates the lens power required for vision correction. Negative numbers refer to nearsightedness while positive numbers refer to farsightedness. The further away from zero, the stronger your prescription.

Cylinder (CYL)

When you have astigmatism, your eye isn’t completely spherical. The cylinder indicates the correction needed due to this anomaly.


The axis indicates the position of the abnormal curve on your cornea. It’s written in degrees (1 to 180) and compensates for astigmatism.


If you have bifocal lenses, this is where the doctor will write the prescription for the bottom half of your lenses.


This is a special prescription that only applies to people with double vision. Glasses with prism fuse the two images together so that people with double vision can see properly.

Contact Lenses Rx

Learn what the different parts of your contact lens prescription mean.


These are Latin abbreviations that stand for the following:

  • OS: ocular sinister or left eye
  • OD: ocular dexter or right eye
  • OU: ocular uterque or both eyes


BC stands for base curve and indicates the back curvature of the lens. Measured in millimeters, it helps guarantee the best fit for your corneal curvature. The steeper the cornea, the lower the BC.


DIA, short for diameter, measures the width of the contact in millimeters. It specifies where the lens will rest. Contact lenses of the wrong diameter cause irritation and abrasion that can injure your eye.


CYL, short for cylinder, appears on your prescription if you have astigmatism. The cylinder is measured in an optical unit called a diopter.


This is another measurement specific to astigmatism. If your prescription contains an axis measurement, it indicates how the cylinder is oriented.


Our eye doctors in Mesa and Chandler use this space in your prescription to include specifications for a bifocal lens, if required.


If you choose a tinted lens to change your eye color, it’s noted on your prescription here.

Contact lenses sit directly on the eye whereas eyeglasses typically rest about 12 millimeters from the eye’s surface. Therefore, you need different prescriptions for these vision correction options. As part of our service to our clients, your eye doctor will also discuss other options for permanent vision correction such as cataract and LASIK surgery in Mesa and Chandler.

Swagel Wootton Eye Institute also specializes in other types of specialty contact lenses to address a multitude of corneal conditions, including rigid gas permeable lenses (RGPs), hybrid lenses, and most commonly scleral lenses. Scleral lenses are complex, often custom-made, lenses designed to exactly fit the contour of any shaped cornea. They are often the only option for patients with keratoconusdry eye, or other corneal irregularities.

We are a leading eye institute in Arizona specializing in cataract, LASIK and other laser correction procedures. Our eye doctors in Mesa and Chandler provide comprehensive eye care for your entire family from the youngest to the oldest members. Contact us today to schedule an eye exam.