OD vs OS: What Do They Mean on an Eye Prescription?
OD means right eye, and OS means left eye. OD stands for oculus dexter, the Latin term for the right eye, while OS stands for oculus sinister, meaning the left eye. On an eyeglass prescription, these abbreviations show which eye each set of prescription values belongs to.
You may also see OU, which stands for oculus uterque and means both eyes. OD, OS, and OU do not describe how strong your prescription is. They simply identify whether a measurement applies to the right eye, left eye, or both eyes.
If you are ordering prescription glasses, make sure the values listed under OD are entered for your right eye and the values under OS are entered for your left eye. Reversing them can result in lenses being made with the prescription values assigned to the wrong eye.
|
Abbreviation |
Latin Term |
Meaning |
Typical Use |
|---|---|---|---|
|
OD |
Oculus dexter |
Right eye |
Right-eye prescription values |
|
OS |
Oculus sinister |
Left eye |
Left-eye prescription values |
|
OU |
Oculus uterque |
Both eyes |
Information that applies to both eyes |
What Do OD and OS Mean on an Eye Prescription?
OD and OS are used to keep the prescription values for each eye clearly separated.
OD identifies the right eye. OS identifies the left eye. Because the two eyes can have different prescription powers, cylinder values, axes, or other corrections, keeping the measurements assigned to the correct eye is essential when prescription lenses are made.
The abbreviations themselves do not indicate whether one eye sees better than the other. They also do not indicate which eye is dominant or whether the prescription is strong or mild.
They are simply labels that tell you which eye the numbers belong to.
Where Do OD and OS Appear?
OD and OS commonly appear on eyeglass prescriptions, contact lens prescriptions, eye examination records, and other clinical documents.
On an eyeglass prescription, the information is usually arranged so that each eye has its own row or column. The values beside OD apply to the right eye, while the values beside OS apply to the left eye.
This matters because the two eyes do not necessarily have identical prescriptions. One eye may be more nearsighted or farsighted than the other, or the amount and orientation of astigmatism may differ.
Why Is Each Eye Listed Separately?
An eyeglass prescription is written eye by eye because each eye has its own optical requirements.
For example, someone might have a sphere value of -2.00 in the right eye and -3.00 in the left eye. Another person may have similar sphere values in both eyes but different cylinder or axis measurements for astigmatism.
OD and OS provide the basic structure that keeps those measurements assigned correctly.
How to Read the Other Values on Your Prescription
OD and OS identify the eye, while the numbers and abbreviations beside them describe the actual prescription.
Common terms include:
- SPH: Sphere power used to correct nearsightedness or farsightedness
- CYL: Cylinder power used when astigmatism is present
- AXIS: The orientation of astigmatism, measured from 0 to 180 degrees
- ADD: Additional near power used for bifocal, progressive, or other multifocal prescriptions
- PRISM: A prescribed correction used for certain binocular vision or eye-alignment needs
- PD: Pupillary distance, used to position prescription lenses relative to the pupils
If you want a full explanation of these terms, see our How to Read an Eye Prescription Guide.
SPH: Sphere
SPH shows the main focusing power prescribed for the eye.
A minus value generally indicates myopia, or nearsightedness, while a plus value generally indicates hyperopia, or farsightedness.
If OD and OS have different sphere values, the right and left lenses will require different optical powers.
CYL and AXIS: Astigmatism Correction
CYL and AXIS are used together when astigmatism correction is prescribed.
CYL indicates the amount of astigmatism correction, while AXIS describes its orientation. Because the axis is specific to each eye, it is important that the OD and OS values remain correctly assigned.
ADD: Near Addition
ADD is additional near power used in multifocal prescriptions such as bifocals and progressive lenses.
The ADD value is often similar or the same for both eyes, but the distance prescription under OD and OS may still differ.
PRISM
Prism may appear on some prescriptions when a specific binocular vision or eye-alignment correction has been prescribed.
Because prism can be prescribed differently for the right and left eyes, the OD and OS labels remain important when the lenses are made.
Why OD and OS Matter When Prescription Lenses Are Made
OD and OS are more than labels on a prescription form. They help ensure that each lens is produced for the correct eye.
The laboratory uses the prescription assigned to OD for the right lens and the prescription assigned to OS for the left lens.
Depending on the prescription, the two lenses may differ in:
- sphere power
- cylinder power
- axis
- prism
- thickness
- optical center position
This is especially noticeable when the prescription differs substantially between the two eyes.
OD, OS, and Pupillary Distance
Pupillary distance, or PD, is another important measurement used when prescription lenses are positioned in a frame.
A PD may be written as one binocular measurement or as two monocular measurements.
For example:
- Binocular PD: 62 mm
- Monocular PD: 31 mm OD / 31 mm OS
Monocular PD measurements describe the distance from the center of the nose to each pupil separately. They can be useful when the right and left sides are not perfectly symmetrical.
If you need help understanding or measuring PD, see our How to Measure Pupillary Distance Guide.
OD and OS in Progressive and Multifocal Prescriptions
OD and OS remain important when progressive, bifocal, or other multifocal lenses are prescribed.
A progressive prescription may include separate sphere, cylinder, and axis values for each eye, together with an ADD value for near vision.
The finished right and left lenses therefore need to be made according to the values assigned to OD and OS while also using the appropriate fitting measurements for the selected frame.
If you are considering progressives, our Progressive Glasses Guide explains how progressive lenses work and what to consider when choosing a frame.
OD and OS in Stronger Prescriptions
OD and OS are particularly useful when the prescription strength differs noticeably between the two eyes.
For example, one eye may require a stronger minus or plus power than the other. That difference can affect the finished thickness and appearance of the lenses.
Frame size, lens shape, lens material, refractive index, and the position of the eyes within the frame can all influence the final result.
If your prescription is strong and lens thickness is a concern, see our High Prescription Glasses Guide.
Common Misunderstandings About OD and OS
OD and OS are simple terms, but they are easy to confuse when reading a prescription for the first time.
Does OD Mean the Stronger Eye?
No. OD simply means right eye. OS means left eye.
Neither abbreviation tells you which eye has the stronger prescription or better vision.
Does OD Mean Doctor of Optometry?
OD can also be used as a professional degree abbreviation for Doctor of Optometry. On an eyeglass prescription, however, the surrounding context usually makes the meaning clear.
If OD appears beside SPH, CYL, AXIS, or other prescription values, it refers to the right eye.
Is OU the Same as OD and OS?
No.
OD refers specifically to the right eye, OS refers specifically to the left eye, and OU refers to both eyes together.
OU may be used when a note or measurement applies to both eyes, but separate OD and OS entries are normally needed when the prescription values differ.
What About RE and LE?
Some prescription forms use RE for right eye and LE for left eye instead of OD and OS.
The meaning is the same; only the notation is different.
What Should You Check Before Ordering Prescription Glasses?
Before submitting a prescription for an online glasses order, check that the information has been entered exactly as written.
Important details include:
- OD: Confirm the right-eye values
- OS: Confirm the left-eye values
- SPH: Check the plus or minus sign carefully
- CYL and AXIS: Enter them exactly as prescribed when present
- ADD: Include it when your lens type requires near addition
- PD: Use the correct binocular or monocular measurement
- PRISM: Include it exactly as prescribed if it appears on the prescription
One of the most important checks is simply making sure that the OD and OS values have not been reversed.
If any part of the prescription is unclear, or if you are unsure whether the prescription is current, confirm the information with your eye-care professional before ordering.
OD vs OS: The Simple Way to Remember Them
The easiest way to remember the terms is:
- OD = Right Eye
- OS = Left Eye
- OU = Both Eyes
Once you know which eye each abbreviation refers to, the rest of the prescription becomes much easier to follow.
OD and OS organize the prescription so that the correct sphere, cylinder, axis, ADD, prism, and other values are assigned to the correct eye. That simple distinction is fundamental when prescription lenses are ordered and made.
Ready to Order Prescription Glasses?
Once you understand which prescription values belong to OD and OS, you can review your prescription more confidently and make sure the right-eye and left-eye information is entered correctly.
Choose a frame that fits your style and measurements, then select the prescription lens options that match your visual needs.