Got your eyeglass prescription in hand and it looks like a foreign language? Don’t worry, you’re not alone. Most people find the abbreviations and numbers a bit baffling at first glance. The good news is, understanding your prescription isn’t as complicated as it seems. Essentially, it’s a detailed blueprint for making lenses that will correct your specific vision issues, whether you’re nearsighted, farsighted, have astigmatism, or need multifocal lenses for reading. This article will break down each section, helping you decipher what those letters and numbers mean for your eyes.
Let’s start with the most fundamental abbreviations you’ll see. These tell you which eye each measurement applies to.
OD: Right Eye
OD stands for Oculus Dexter. In plain English, this means your right eye. You’ll always see the prescription details for your right eye listed under this heading first.
OS: Left Eye
OS stands for Oculus Sinister. As you might guess, this refers to your left eye. The details for your left eye will follow the OD information.
OU: Both Eyes
OU stands for Oculus Uterque. This abbreviation indicates that the measurement or prescription is the same for both eyes. While less common for individual corrective powers, you might see it for certain measurements that apply universally to both eyes, or if your vision correction is identical in each eye which is rare. When you see it, it means the information applies equally to your right and left eyes.
Understanding Spherical and Cylindrical Power
This is where the bulk of your vision correction information lies. It dictates the primary strength of your lenses.
SPH: Spherical Sphere Power
The SPH column tells you the main lens power required to correct your vision. This is measured in diopters (D).
Nearsightedness (Myopia)
If you have a minus sign (-) before the number in the SPH column, you are nearsighted. This means you have difficulty seeing distant objects clearly. The larger the number after the minus sign, the stronger your prescription and the more nearsighted you are. For example, -2.00 D is a stronger correction than -0.75 D. These lenses are concave and spread light before it reaches your eye, moving the focal point further back onto your retina.
Farsightedness (Hyperopia)
A plus sign (+) before the number in the SPH column indicates you are farsighted. This suggests you have trouble seeing close-up objects clearly, though severe farsightedness can affect all distances. Similar to nearsightedness, a higher number after the plus sign means a stronger prescription. For instance, +3.50 D signifies a greater degree of farsightedness than +1.00 D. These lenses are convex and converge light, moving the focal point forward onto your retina.
“Plano” or “PL”
Sometimes, you might see “Plano” or “PL” in the SPH column. This indicates that no spherical correction is needed for that particular eye. Effectively, it means 0.00 diopters of spherical power. Your vision is clear enough without this correction, but you might still have astigmatism or other prescriptive needs.
CYL: Cylindrical Power
This column addresses astigmatism, a common condition where your eye’s cornea or lens has an irregular curvature, leading to blurred or distorted vision at all distances.
Amount of Astigmatism
The number in the CYL column, like SPH, is measured in diopters. It usually has a minus sign (-), but occasionally a plus sign (+) depending on the optometrist’s charting system (though minus is far more common). This number indicates the strength of the cylindrical lens needed to correct your astigmatism. No number or “0.00” in this column means you don’t have astigmatism. A higher number, whether positive or negative, means more astigmatism. For example, -1.50 D CYL indicates more astigmatism than -0.50 D CYL.
Impact on Vision
Think of astigmatism as your eye being shaped more like a football than a basketball. This irregular shape causes light to focus unevenly on your retina, leading to blurry vision in certain directions. The cylindrical lens works to counteract this irregularity, bending light more in one specific meridian than others.
The Axis and Addition Power
These two sections provide crucial details for how the cylindrical power is oriented and if you need additional power for reading.
AXIS: Axis for Astigmatism
If you have a number in the CYL column, there will always be a corresponding number in the AXIS column. This number ranges from 1 to 180 and indicates the orientation or meridian of your astigmatism.
Orientation of Correction
The AXIS tells the optician precisely how to position the cylindrical lens to correct your astigmatism. Imagine a protractor laid over your eye, with 90 degrees representing the vertical meridian and 180 degrees representing the horizontal meridian. An AXIS of 90 means the astigmatism is vertical, while an AXIS of 180 means it is horizontal. An AXIS of 45 would be diagonal. This precise alignment is critical; even a slight rotation can make the correction ineffective and cause eye strain or blur. The AXIS measurement is not a measure of power but rather a directional indicator.
ADD: Additional Magnification Power
The ADD column is primarily for people who need extra power for reading or close-up work. This is common for individuals over 40 experiencing presbyopia.
Presbyopia: Age-Related Farsightedness
Presbyopia is a natural, age-related condition where the eye’s natural lens loses its flexibility, making it harder to focus on near objects. The ADD power is the extra magnification layered onto your distance prescription to help you see up close. This is why you often see this on bifocal, trifocal, or progressive lenses.
How It Works
The ADD power is always a positive number and is usually the same for both eyes. For example, if your distance prescription is -2.00 D SPH and your ADD is +2.00 D, your reading prescription would effectively be 0.00 D SPH (-2.00 D + +2.00 D = 0.00 D) for that eye. This additional power is simply added to the spherical power in the lower portion of multifocal lenses. The numbers typically range from +0.75 D to +3.00 D, increasing as presbyopia progresses.
Prism and Pupillary Distance: Finer Details
These measurements are less common on basic prescriptions but are important for specific vision needs.
PRISM: Prism Correction
Prism correction is needed when your eyes don’t align perfectly. It helps correct double vision or eye strain.
Correcting Eye Alignment Issues
If your eyes tend to drift inward or outward, or if one eye is higher or lower than the other, your brain receives two slightly different images. A prism in your lenses redirects light before it enters your eye, aligning the images and helping your eyes work together more comfortably. This can alleviate symptoms like headaches, eye strain, and double vision.
Prism Details: Power and Base
On your prescription, prism will be noted with a number (the power, measured in prism diopters) and a direction (the base). The base indicates the thickest edge of the prism, which is where the light is bent. Common base directions include:
- BO (Base Out): For eyes that drift inward. The thickest part of the prism is towards your temples.
- BI (Base In): For eyes that drift outward. The thickest part of the prism is towards your nose.
- BU (Base Up): For one eye being lower than the other. The thickest part of the prism is upwards.
- BD (Base Down): For one eye being higher than the other. The thickest part of the prism is downwards.
You might see a combination, for example, 1.00Δ BI. This means 1 prism diopter, base in. The prism prescription is often specific to each eye.
PD: Pupillary Distance
Pupillary distance, or PD, is the measurement of the distance between the centers of your pupils.
Why PD Matters
This measurement is crucial for correctly positioning the optical center of your lenses. If your PD is inaccurate, the optical center of your lenses won’t align with your pupils, which can lead to eye strain, headaches, and blurry vision, even if the rest of your prescription is correct. It ensures you are looking through the most effective part of your lenses.
Common PD Formats
- Single PD: A single number, like “62mm,” means the measurement is for both eyes combined. The optical lab will divide this by two for each lens.
- Dual PD: Two numbers, like “31/31mm” or “32/30mm,” indicate separate measurements for each eye (right eye first, then left). This is often more precise. For example, 31/31mm means both pupils are 31mm from the center of your nose, while 32/30mm means your right pupil is 32mm from the center and your left is 30mm. These slight differences are normal.
Where You Find It
Sometimes, PD is included on your eyeglass prescription. Other times, the optician or the optical dispenser will measure it separately. It’s not uncommon for it to be left off the prescription itself, as it’s a measurement taken during the ordering process rather than a refractive error correction. If you’re ordering glasses online, you may need to measure it yourself or ask your optometrist for it.
Lens Type and Other Considerations
| Prescription Term | Meaning |
|---|---|
| OD | Right eye |
| OS | Left eye |
| SPH | Sphere, indicates the amount of lens power needed to correct nearsightedness or farsightedness |
| CYL | Cylinder, indicates the amount of lens power needed to correct astigmatism |
| AXIS | Axis, indicates the orientation of the cylinder power needed to correct astigmatism |
| ADD | Addition, indicates the additional magnifying power needed for reading or close-up work |
Beyond the numbers, your prescription might include notes about the type of lenses recommended or any special coatings.
Lens Type Recommendations
Sometimes, your eye doctor will recommend a specific type of lens based on your vision needs and lifestyle.
Single Vision Lenses
These lenses have one corrective power throughout the entire lens and are used for correcting distance vision, intermediate vision, or near vision, but not a combination. If you only need correction for nearsightedness or farsightedness, without presbyopia, you’ll likely have single vision lenses.
Multifocal Lenses
This category includes bifocals, trifocals, and progressive lenses.
- Bifocals: Have two distinct optical powers, usually a larger area for distance vision and a smaller segment in the lower part for reading. There is a visible line separating these two zones.
- Trifocals: Similar to bifocals but add a third segment for intermediate vision, useful for computer work. These have two visible lines.
- Progressive Lenses (No-Line Bifocals): Offer a seamless transition of power from distance vision at the top, through intermediate vision in the middle, to near vision at the bottom. There are no visible lines, making them aesthetically popular and providing a more natural vision experience, though they can take some getting used to. Your prescription will indicate if an ADD power is included.
Special Coatings and Treatments
While not strictly part of your refractive prescription, these recommendations enhance the functionality and durability of your glasses. Your eye doctor might suggest them, or you’ll discuss them with the optical dispenser.
Anti-Reflective (AR) Coating
This coating reduces glare from light reflecting off the surface of your lenses, improving clarity and reducing eye strain, particularly useful for night driving and computer use. It also makes your lenses almost invisible, enhancing the appearance of your glasses.
UV Protection
Built into or coated onto lenses, UV protection blocks harmful ultraviolet rays, protecting your eyes from sun damage. This is a crucial health benefit, regardless of whether your lenses are clear or tinted.
Scratch-Resistant Coating
While no lens is entirely scratch-proof, this coating makes them more resistant to daily wear and tear, extending the life of your lenses.
Blue Light Filtering
With increased digital screen use, blue light filtering coatings are becoming popular. They aim to reduce exposure to blue light emitted from screens, which some believe can contribute to eye strain and sleep disruption.
Photochromic Lenses (Transitions)
These lenses darken automatically when exposed to UV light outdoors and return to clear indoors, eliminating the need for separate prescription sunglasses. The speed and degree of darkening can vary.
Getting Your Glasses Made
Once you understand your prescription, the next step is getting your glasses made.
The Role of Your Optician
Your optician or optical dispenser takes your detailed prescription and translates it into the physical lenses. They will also consider your frame choice, taking measurements to ensure the lenses are properly centered in the frames for your eyes. This is where your PD measurement becomes critical. They might discuss lens materials, thickness (especially for stronger prescriptions to avoid “coke bottle” lenses), and any recommended coatings or treatments.
Verify Your Prescription
It’s a good practice to double-check that the details on your physical prescription match what you’ve ordered, especially if you’re purchasing online. Ensure the OD/OS, SPH, CYL, AXIS, ADD, and any PRISM values are correctly transcribed. An error in even one number or sign can lead to uncomfortable or incorrect vision correction.
Follow-Up and Adjustments
Once you receive your new glasses, wear them as directed by your optician or eye doctor. If you experience persistent discomfort, blurriness, headaches, or eye strain after an initial adjustment period (which can sometimes take a few days, especially for progressives), don’t hesitate to contact your optician or eye doctor. Sometimes minor adjustments to the frame fit or even a re-check of the prescription might be needed. Your vision health is important, and clear, comfortable vision is the goal.
FAQs
What information is included in an eyeglass prescription?
An eyeglass prescription typically includes the patient’s name, the prescribing doctor’s name, the prescription date, the sphere (SPH), cylinder (CYL), axis, and pupillary distance (PD) measurements.
What do the sphere (SPH), cylinder (CYL), and axis measurements mean in an eyeglass prescription?
The sphere (SPH) measurement indicates the amount of lens power needed to correct nearsightedness or farsightedness. The cylinder (CYL) measurement indicates the amount of lens power needed to correct astigmatism. The axis measurement specifies the orientation of the cylinder power in the lens.
How is the pupillary distance (PD) measured and why is it important?
The pupillary distance (PD) is the distance between the centers of the pupils in millimeters. It is important because it ensures that the optical center of the lenses aligns with the center of the pupils, providing the most accurate vision correction.
Can I use my eyeglass prescription to purchase glasses online?
Yes, many online retailers accept eyeglass prescriptions for purchasing glasses. However, it is important to ensure that the prescription is up to date and accurately filled out to ensure the correct lenses are made.
How often should I have my eyeglass prescription checked?
It is recommended to have your eyeglass prescription checked annually, or as advised by your eye care professional. Changes in vision can occur over time, and regular check-ups ensure that your prescription is up to date and providing the best vision correction.