You just left your optometry appointment with a newly issued optical prescription. You look down at the slip of paper, expecting straightforward numbers, but instead, you are greeted by a grid of obscure medical abbreviations: OD, OS, SPH, CYL, AXIS, ADD, and PD.
When ordering prescription glasses online, entering these numbers incorrectly by even a single digit or misplaced plus/minus sign can lead to blurry vision, eye strain, or sudden headaches.
Here is an optical lab guide on how to read your glasses prescription, what each medical abbreviation means, how to calculate your Reading ADD power, and how to select the right optical lens coatings without overpaying.
The Key Eyeglass Prescription Terms Explained
According to clinical guidelines from the American Academy of Ophthalmology, an optical prescription is a medical blueprint designed to bend light precisely onto your retina. Here is what each column means:
1. OD vs. OS (Which Eye is Which?)
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OD (Oculus Dexter): Latin for "Right Eye."
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OS (Oculus Sinister): Latin for "Left Eye."
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OU (Oculus Uterque): Latin for "Both Eyes" (less common, used when both eyes share identical power).
2. SPH (Sphere / Optical Power)
Indicates the overall lens power required to correct your vision, measured in Diopters (D).
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Minus Sign (–): Indicates Nearsightedness (Myopia) — you see well up close, but distant objects appear blurry.
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Plus Sign (+): Indicates Fearsightedness (Hyperopia) — distant vision is clear, but close-up text requires effort.
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Note: The further the number is from zero (e.g., -5.50 vs -1.25), the stronger your prescription requirement.
3. CYL & AXIS (Astigmatism Correction)
If these two boxes are filled out on your prescription, you have astigmatism — an oval or football-shaped curvature of your eye's cornea.
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CYL (Cylinder): Represents the extra lens power needed to smooth out corneal unevenness.
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AXIS (1° to 180°): The orientation angle showing where the astigmatism correction needs to sit in your frame.
What Is "ADD" on an Eye Prescription?
The ADD (Addition) power is one of the most frequently misunderstood numbers on an optical prescription.
ADD represents the additional magnifying power added to the lower portion of a lens to correct Presbyopia — the natural aging process of the eye's crystalline lens that makes reading small print difficult (typically starting around age 40+).
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Always a Plus (+) Number: ADD values typically range from +0.75 to +3.00 D in +0.25 increments.
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Used for Bifocals & Progressives: If your prescription includes an ADD value, you qualify for Progressive No-Line Lenses or dedicated Reading Glasses.
How to Convert a Progressive Prescription to Single Vision Reading Glasses
If you have a progressive prescription but only want dedicated, single-vision reading glasses, use this simple optical formula:
Reading SPH = Distance SPH + ADD Power
Example: If your Distance SPH is -2.00 and your ADD is +1.50, your Reading SPH becomes -0.50 (Keep CYL and AXIS unchanged).
Essential Lens Add-Ons & Coatings: What Do You Really Need?
When customizing your prescription glasses online, you will encounter various lens treatments. Here is a breakdown of essential coatings versus unnecessary markups:
| Lens Treatment / Coating | Primary Benefit | Recommended For |
| Anti-Reflective (AR) Coating | Eliminates lens glare, halos from streetlights, and cosmetic reflections in photos. | Essential for all wearers (especially night drivers and screen users). |
| UV400 Protection | Blocks 100% of damaging UVA & UVB radiation from reaching the retina. | Essential for all wearers (Included standard at PHANEO). |
| Blue Light Filtering | Filters high-energy visible (HEV) light emitted by digital displays and LED lighting. | Office workers, gamers, and heavy smartphone users. |
| High-Index Refractive Material | Thins out thick, heavy lens edges for strong prescriptions (1.61, 1.67, 1.74). | Prescriptions over ±3.00 SPH. |
The M2C Difference: Premium Prescription Accuracy Starting at $6.59
Traditional optical boutiques frequently charge $50 to $100 extra for anti-scratch, anti-glare, and UV coatings as separate "add-on" upsells.
At PHANEO, we believe essential eye protection is not an optional luxury. Our optical manufacturing lab integrates multi-layer anti-reflective coatings and UV400 filters directly into our factory-direct prescription lenses — delivering custom-made prescription eyewear starting at just $6.59.
Frequently Asked Questions
Q: Is my contact lens prescription the same as my glasses prescription?
A: No. Contact lenses sit directly on your cornea, whereas eyeglasses sit roughly 12 mm away from your eye. Eyeglass prescriptions require specific vertex distance adjustments and cannot be used to order contacts.
Q: What does PD stand for and why is it mandatory?
A: Pupillary Distance (PD) is the exact distance (in millimeters) between the centers of your pupils. It ensures the optical center of each lens aligns perfectly with your eyes to prevent double vision or visual strain.
Q: How long is an eyeglass prescription valid?
A: Eyeglass prescriptions are generally valid for 1 to 2 years, depending on state regulations and the optometrist's recommendation.
Get Medical-Grade Precision Direct From the Lab
Reading your eye prescription doesn't have to be confusing. Once you have your SPH, CYL, AXIS, and PD values ready, entering them into PHANEO's streamlined ordering tool takes less than two minutes.
Skip the retail markups and experience lab-direct precision today.
Order Custom Prescription Glasses Direct From PHANEO Starting at $6.59 →
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