How to read eye prescription (od vs os included)

A telltale sign that you need eyeglasses is that you suffer from frequent headaches. Your doctor might recommend that you have your eyes tested. Other major reasons for an eye test are that you begin to have blurry vision and have to keep reading material at a distance.

Blurry vision is called refractive error and requires glasses. Your eye test will reveal whether you have one of the following refractive errors: nearsightedness, astigmatism, presbyopia, or farsightedness.

One of the absolute necessities for eyeglasses is your eye prescription. You cannot get a pair of eyeglasses if you do not have an eye test. In recent years, many optometrists have done separate eye tests or given you a package with the eye test included.

A separate eye prescription allows you to have the option of choosing frames from different outlets. However, you must note that in such cases, the eye test will come with a disclaimer. For that reason, it is important for you to know how to read eye prescription.

OD vs OS

There are some necessary terms we must remember before learning more about how to read an eye prescription. OD and OS are two simple yet important abbreviations.

OD means "right eye" and OS means "left eye," which are shortened from the Latin terms oculus dexter and oculus sinister. 

What is an eye prescription?

Generally speaking, optical prescriptions are printed or handwritten by the optometrist, both of which are accepted:

1. Handwritten prescription

2. Printed optical prescription

Some of the elements included in an eye test will provide information specifically for:

1. Prescription for your left eye – LE or OS (Left Eye)

2. Prescription for your right eye – RE or OD (Right Eye)

Most optometrists use OS and OD, but in recent times, some optometrists have opted for the English abbreviations LE and RE instead.

3. How the lens will refract light – SPH (Sphere of the eye)

4. If you have astigmatism it will include the correction number – CYL (Cylinder of the eye)

5. The units of measurement for the optical power of the lens are diopters. These are the measurement units used to determine the optical power of the lens.

6. The additional correction numbers needed for close focusing are the ADD measurements.

The optometrists have specialized equipment to do all the testing and measurements required to meet these requirements. These state-of-the-art testing facilities allow them to make further medical referrals if there are any problems that lenses cannot fix.

How to read an eye prescription?

According to different usage, common types of optical prescriptions are at the following:

1. Prescription of distance and reading

RT or OD or RE or R: The Right Eye

LT or OS or LE or L: The Left Eye

OU or BE: The Eyes

AXIS: The axis of the cylinder lens. The astigmatism axis takes the angle between the cylinder axis and the horizontal line as the standard, and is currently marked by TABO labeling method, where the horizontal dimension is not called 0°, but 180°.

S: Spherical lens, (-) for myopia and (+) for yperopia or presbyopia

C: Cylindrical lens, used for astigmatism

DS: Focal power of the spherical lens

DC: Focal power of the cylindrical lens

PD(Pupillary distance): The distance in millimeters between the centers of pupils

In particular, each degree is marked with a symbol, and each symbol represents different numbers of degrees. Make sure that they are correct.

2. The prescription of progressive and bifocal

Add: The addition of luminosity, presbyopia, bifocals and progressive lenses

PH(Pupil Height): The height measured in millimeters of the pupil center on the lens

Compared with the prescription of distance and reading, prescriptions of progressive and bifocal add an NV or ADD parameter, which can be filled according to the optometric forms.

3. The prescription of trifocal

Prism Degree Notation:

P: Prism unit of triple prism(△)

B: The direction of the prism base

BI: Basal inward (base near the nasal side)

BO: Basal outward (base near the temporal side)

BU: Basal upward

BD: Basal downward

You will find that getting a separate eye prescription will give you more options when choosing glasses. For this reason, you should know how to read eye prescription. In the previous section, we showed you some of the abbreviations that are used on the prescription.

By knowing what these are, you are able to read your prescription. Both eyes are tested separately, which will be recorded as OD or OS (right eye or left eye). Each of these is assigned a number for distance and ADD. Of specific importance is the number under SPH. Additional numbers are allocated under CYL, axis, prism, and base.

You can determine the weakness of your eyes by how far away from zero the number is on your prescription. The farther away, your eyesight will need more correction, which means a stronger prescription. If you are farsighted, the allocated number will have a plus sign. If you are nearsighted, the allocated number will have a minus sign. Included will also be the distance between the centers of the pupils, which is the pupillary distance (PD). See below for an example.

Other parameters of optical presciptions

PAL: Progressive Addition (or Adjustment) Lens. Sometimes on a Progressive Rx an eye Dr. will write two different numbers for the NV-ADD to increase the reading power in the NV-ADD for Progressive lenses.

PL: Plano. Latin for "flat." If this is in the SPH section of an Rx, it means no nearsighted or farsighted correction is needed.

BAL: the Rx calls for balance lenses, meaning the same Rx for each eye. Often used when a person has no sight in one eye, so both lenses will have the same thickness.

Tips to Find the Right Glasses with Your Eye Prescription

Lensmart offers you a wide range of frames that will help you choose your lenses. One of the best ways to choose your glasses with your prescription is to choose a larger frame, such as Nors. The reason for this is that it will offer more comfort, especially if you have a prescription for multifocals.

An excellent choice for your single vision prescription is to choose a smaller frame. Finley or other rectangle glasses are an excellent choice. 

How to find the right glasses for you is as follows:

1. First of all, know how to read your eye prescription. It will give you an advantage when choosing your glasses. It will help you choose the frame that is best for you.

2. Make sure you know your pupillary distance (PD) so that your lenses are fitted correctly.

3. Always keep in mind all the other elements that would help you find the right glasses. As with all glasses, choose the right ones for your face shape, skin color, and so forth.

Recommended articles:

All explained: how to know if you need glasses

What is CYL, AXIS and SPH in eye prescription?

Pupillary distance explained: how to measure PD

Explained: Why do new glasses make you dizzy?

What are 20/10, 20/20, and 20/40 vision?

Everything about an eye exam you should know

Astigmatism vs. normal: all you need to know

Explained: how to adjust your glasses at home properly