If you have ever gotten a prescription for glasses or contacts, it probably looks something like the above. But what do all the numbers and columns mean? Let’s break it down.
First, every prescription will have the date it was provided to you, the date it was prescribed to you, and how long the prescription is good for. Prescriptions expire because your eyes change and what you need now could be very different from what you need a year from now.
You’ll also notice the information of the practice that provided the prescription, the doctor's signature, and the doctor’s license number. Your name, address, date of birth, and phone number are also included to ensure that the prescription is indeed yours.
All of that is pretty straightforward. Let’s move on to the more complicated stuff.
To the far left of the prescription, you’ll see the abbreviations RT and LT. These are, quite literally, right and left and refer to which eye the prescription is for. You may also see it written as OD and OS. OD derives from the Latin for Right Eye and OS derives from the Latin for Left Eye. I had never seen a prescription form where RT/OD was not on top of LT/OS.
Depending on your age, you may also have an additional column on your prescription even further left that reads D.V. and N.V. This refers to distance vision and near vision respectively.
Not too complicated, but needs explained at least once.
Now what about the rest of the columns?
Sphere – Refers to your corrective power, or the strength of the lens necessary to allow you to see 20/20. In a patient with no astigmatism, no need for bifocals, and proper eye alignment, this will be the only column with numbers in it. It is the root of the prescription.
Cylinder – The cylinder columns indicates the corrective power needed for astigmatism. In a patient with 20/20 vision, but an astigmatism that needs correcting, the sphere column will be empty or 0, while the cylinder and axis columns have values.
Axis – Astigmatism is a vision disturbance in one specific point along the meridian of your vision that ‘skews’ it. The axis in your prescription refers to the degree/direction of the astigmatism to be corrected so the correction for it is placed in the correct area.
Prism – sometimes one column, sometimes two (horizontal [hz] & vertical [vt]), the prism column indicates if a prism is necessary in the glasses to encourage eye alignment. In a contact lens prescription, the prism column will be missing or blank as prisms are currently specific to glasses.
Add – this is for bifocals. An add is the corrective power at the bottom half of the bifocal that “softens” or “lessens” the correction needed for distance so near vision is more comfortable.
Finally, you’ll see some variation of PD on your prescription. Every pad seems to have it in a different place. Some prescriptions will break it into Near PD and Distance PD. PD stands for pupillary distance and is how far about the center of your eyes are from each other. Especially for the prescriptions with axis and prisms, this is a very important measurement to get correct. There are some guides online on how to measure this yourself, but best practice is to ensure your eye doctor just writes it down on your prescription, especially if you are planning on ordering glasses from somewhere that isn’t your doctor’s office.
And that’s how to read a prescription!
Now you may be wondering, “Why is my glasses prescription different than my contact lens prescription”. The very simple answer is your contacts are directly against the eye while glasses are up to an inch away from it so the correction power needed is going to differ. How much it differs will depend on the individual and the contact lens brand.
No matter your prescription, if your main form of vision correction is Daily Contact Lenses, check out our DailyLens to tackle the hassle of your contact lens routine. No mess, no stress, just vision.
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