What Your Prescription Numbers Really Mean and How to Read Them

You’ve likely looked at your contact lens and eyeglasses prescription and thought it looked like a complicated math equation. These abbreviations and numbers are the blueprints for clear vision and are unique to every patient.

This sheet of paper outlines the vision correction power required to allow you to see clearly with corrective eyewear. Our eye doctors at The Laser Eye Center™ in Southern California explain how to read your vision prescription. 

Abbreviations on Your Vision Prescription 

One of the first things you may notice about your prescription is the abbreviations used on the paper. OD, OS and OU are used to prescribe contact lenses, eyeglasses and medications for eye diseases or conditions. Oculus dexter (OD) represents your right eye and oculus sinister (OS) your left. Oculus uterque (OU) describes both eyes. Other abbreviations used in vision prescriptions include: 

• SPH: The sphere portion of your prescription lists your lens power. The lens power corrects your eyesight for myopia (nearsightedness) and hyperopia (farsightedness). A minus sign indicates nearsightedness, and a plus sign or the absence of a quantifier means that you are farsighted. 

• CYL: The cylinder part of your vision prescription represents the degree of astigmatism. This area may be blank if you do not have astigmatism. The minus and plus signs are also used in this column to designate nearsighted astigmatism or farsighted astigmatism, respectively. 

Other areas of your vision prescription indicate the axis, add and prism.

The axis section defines the astigmatism direction, such as horizontal astigmatism of 180 degrees. The add portion shows the required magnifying power to accommodate presbyopia. Presbyopia is the age-related loss of near vision that occurs when the natural eye lens hardens and loses its flexibility and ability to adapt for clear close-up eyesight.

The “add” is used at the bottom of multifocal lenses or “bifocals” and typically applies to people over 40. This number may have a plus sign and applies to both eyes. 

The final section of your vision prescription is the prism. The prism compensates for misaligned eyes. Some prescriptions require a prismatic power to correct your vision while accommodating alignment concerns. BO- base out, BU- base up, BD- base down and BI- base indicate prism power. 

Schedule Your Eye Exam at The Laser Eye Center™ 

If you have questions about your vision prescription or it’s time for an eye exam, contact our eye doctors at The Laser Eye Center™ to schedule an appointment today.