Understanding Contact Lens Prescriptions: What Do the Numbers Mean?

Trying to understand your contact lens prescription can be difficult for most people. Optical prescriptions have standard abbreviations, making it easy to dispense correct lenses. Eye doctors use various letters and numbers to describe different eye parts.
 

Contact lens prescriptions differ from eyeglass prescriptions in the information they contain. Here’s how you can understand contact lens prescriptions and what the numbers mean.
 

Contact Lens Prescriptions

As more people shop online to save money, knowing what you are buying is critical. Are you planning to buy your contact lenses from a source different from where you got the exam? It can help to understand your prescription.
 

You cannot use your eyeglass prescription to buy contacts. Contact lens prescriptions contain information not in glasses prescriptions as the contacts rest directly on the eye.
 

Reading Your Lens Prescription

Reading your contact lens prescription will require understanding your eye power or sphere, diameter, base curve, and brand. A basic prescription is usually in table format.
 

The different markers allow optometrists to provide vital information about your eyes and the correction needed to improve your vision. You may require different correction for each eye, making the figures for each eye different.
 

What the Letters in the Prescription Mean

OD and OS: The letters appear along the top or side of the prescription. OD (Oculus Dexter) is Latin for the right eye, and OS (Oculus Sinister) describes the left eye. If your prescription has the letters OU (Oculus Uterque), the measurements are similar for both eyes.
 

PWR: The letters refer to refractive power. Sometimes, the measurement is called SPH (sphere). It is the amount of correction needed to bring the vision as close as possible to perfection (20/20). The measurement is in diopters. If there is a minus before the number, you have myopia. A plus sign shows hyperopia. Most people have different prescriptions for each eye.
 

DIA: The lens diameter determines where the lens will sit on the eye surface. The figure is in millimeters, typically between 13 and 15. Correct measurement helps to ensure the contact lens fits comfortably and does not scratch the eye.
 

BC: The letters describe the Base Curve. The contact lens curvature allows the contact lens to fit perfectly on the eye surface. This number helps to ensure the lenses are the right size to accommodate the cornea. The measurement is in millimeters. Some contact lens brands only come in one base curve.
 

Specialized Contact Lenses

If you require toric lenses for astigmatism, the prescription will have additional measurements. The prescription contains the abbreviations CYL or cylinder and AXIS. The cylinder value is the power required to correct astigmatism.
 

The number is usually between -4 and +4. Axis is the cylinder value orientation and is a number between 0 and180°. Some prescriptions, especially bifocal or multifocal lenses, have the letters ADD for added magnifying power.
 

Brand and Color

A contact lens prescription may contain information about the brand, color, and other details. This is the case if the eye doctor feels a specific brand offers the best lens option for your condition.
 

The prescription may also contain usage information or instructions on how often to replace the lenses. Most contact lens prescriptions last one or two years from the date of the exam.
 

For more on contact lens prescriptions and what the numbers mean, visit Westside Vision Optometry. Our office is in Los Angeles, California. Call (424) 249-1957 to book an appointment today.

https://www.healthline.com/health/how-to-read-eye-prescription

https://www.medicalnewstoday.com/articles/how-bad-is-my-eye-prescription