Reading and understanding your eyeglasses prescription

If you've ever looked at your glasses prescription 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 eyeglass prescription and what's behind all those letters in that scribbly, hard-to-read eye doctor's handwriting. To put it simply, the further away from zero the number on your prescription is, the more vision correction you need. A plus (+) sign in front of the number means you are farsighted, while a minus (-) sign means you are nearsighted.

Now let’s learn about the different types of prescriptions.

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 Prescriptions

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

Progressive-Vision Prescriptions

A progressive-vision prescription corrects for multiple fields of vision: typically distance, intermediate, and near/reading all in one eyeglass 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 eye alignment problems and experience difficulty focusing, eye fatigue, limited depth perception, and double vision, it's possible you have a prism prescription. The number under ‘Prism’ is the amount of prescribed prismatic power, which is measured in prism diopters, denoted by a triangle:

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 consists of three measurements: sphere, cylinder, and axis. These numbers can also tell you what type of vision correction you need. It is important to know how to measure sunglasses so you get the right fit, along with the proper prescription.

SPH = Sphere

The sphere number indicates if you have nearsighted or farsighted vision. The number indicates lens power, and 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 astigmatism correction in the lens. For example:

Cylinder and Axis Prescription Example

A minus sign in the cylinder column denotes nearsighted astigmatism, and a plus sign in the column denotes farsighted astigmatism. If your prescription shows nothing in the cylinder column, you’re in luck, and you don’t have astigmatism, or if you do, it’s not worth correcting because your degree of astigmatism is minute. If you do have astigmatism, make sure to use sunglasses protection, since astigmatism can get worse with age.

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.

Understanding Your Prescription with Revant Optics

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