How to read and understand everything about your eyeglasses prescription

If you’ve ever looked at the prescription for your glasses, and felt it has more confusing acronyms than a text conversation between two teenagers you’re not alone. We’re here to help you better understand your prescription and what’s behind all those letters in that scribbly, hard-to-read doctor’s handwriting.

Example prescription form with definitions of key terms

Single or progressive prescriptions

Most prescriptions fall within one of two categories, single or progressive. Here’s a brief explanation of both. 

Single-Vision Prescription

A single-vision prescription corrects for one field of vision: immediate or near distance. Glasses with this lens type correct nearsightedness or farsightedness.

Progressive-Vision Prescription

A progressive-vision prescription corrects for multiple fields of vision: typically distance, intermediate, and near/reading all in one lens. Progressive lenses are multi-focal with three viewing areas with no visible lines between each area.

Single Vision vs Progressive Vision

Prism prescriptions

If you have vision alignment issues and experience difficulty focusing, eye fatigue, limited depth perception, and double vision, it's possible you have a prism prescription. 

Prism and Base Prescription Example

Reading your prescription for eyeglass lenses 

Here are the basics  

OD, OS = Right eye, left eye

And in more detail…

OD = Oculus Dexter (the right eye)

OS = Oculus Sinister (the left eye)

OU = Oculus Uterque (both eyes) 

PD = Pupillary distance

The distance between the pupils in your eyes is known as pupillary distance (PD). With prescription glasses, your PD is your “optical center,” or where you look through your lenses when staring straight ahead. 

SPH, CYL, AXIS = Sphere, cylinder and axis.

Each eye prescription is comprised of three measurements: sphere, cylinder, and axis. These numbers can also tell you what type of vision correction you need. 

SPH = Sphere

The sphere number indicates if you have nearsighted or farsighted vision. It is measured in a unit called a diopter or, “D.” If you are nearsighted, this measurement will be a negative number with a ( - ) symbol. If you’re farsighted, this measurement is usually a positive number with a ( + ) symbol. The higher the number, the stronger the correction.

Farsighted vs Nearsighted

CYL = Cylinder & Axis

If your eyes have astigmatism (a slightly oval-shaped cornea) they typically require a lens with a cylindrical curve. This type of prescription has a cylinder and an axis number (1°-180°), which both tell the lens maker where to place the correction in the lens. For example:

Cylinder and Axis Prescription Example

Segment Height

This measurement is used to accurately place the progressive power on your lenses. It is the height from the bottom of the lens to the center of your pupil when wearing the glasses. We'll need this value for any progressive orders.

ADD Value

This measurement is used to accurately place the progressive power on your lenses. It is the height from the bottom of the lens to the center of your pupil when wearing the glasses. We'll need this value for any progressive orders.

So now that you’re a pro at reading your eyewear prescription, you can update your glasses anytime without even having to leave home. At Revant, we make custom-cut prescription lenses for any frame and hand-install them with precision. From start to finish, the process takes only a few weeks and your glasses are shipped directly to your door. 

Shop our prescription lenses here.