Prescription knowledge center
How to read a glasses prescription
Decode eyeglass prescription fields in plain language, explore PD and astigmatism notation, and use the interactive decoder. Educational explanations only — not a substitute for your written prescription or an eye exam.
Featured tools
Interactive educational tools related to this topic.
Prescription Decoder
Paste or enter OD/OS sphere, cylinder, axis, ADD, prism, and PD to get plain-English educational explanations.
Pupillary Distance
Learn what PD means, explore single vs dual PD, and practice educational measurement concepts for glasses fitting.
Reading ADD Explainer
Learn what ADD means for progressive, bifocal, and reading lenses — educational ranges only, not a prescription.
Frame Size
Decode eye size, bridge, and temple measurements such as 52□18 140 and learn how frame fit works.
Prescription basics
Core eyeglass prescription fields and how to read them.
OD (Right Eye) on a Glasses Prescription
OD means oculus dexter—the right eye. Learn how OD columns work with OS, why eyes differ, and how to read right-eye powers without myths.
OS (Left Eye) on a Glasses Prescription
OS means oculus sinister—the left eye. Learn left-eye prescription layout, OS vs OD differences, and how to avoid left/right mix-ups when ordering lenses.
OU (Both Eyes) on a Glasses Prescription
OU means both eyes. See when OU appears, how it relates to OD/OS, and why binocular notes are not a shortcut past monocular powers.
Sphere (SPH) on a Glasses Prescription
Sphere is the primary focusing power in diopters. Learn plus vs minus sphere without false acuity claims.
Cylinder (CYL) on a Glasses Prescription
Cylinder power corrects astigmatism in a glasses prescription. Learn how CYL works with axis—and what magnitude does not prove.
Axis on a Glasses Prescription
Axis (0–180°) orients cylindrical correction. Learn what axis does and does not mean—and why it is not a severity score.
ADD Power on a Glasses Prescription
ADD is near addition power for bifocals and progressives. Educational overview of near-focus support—not a DIY reader prescription.
Prism on a Glasses Prescription
Prism diopters can be prescribed for binocular alignment needs. Learn educational basics without self-diagnosing double vision.
Prism Base Direction Explained
Base in, out, up, or down describes prism orientation. Educational guide to base notation and why reversing base reverses effect.
PD on a Glasses Prescription
Pupillary distance helps center lenses. Learn how PD appears with prescriptions and orders—and why DIY PD can fail for progressives.
Plano (PL / 0.00) on a Glasses Prescription
Plano means no spherical powered correction in that field. Learn how PL/0.00 interacts with cylinder, balance lenses, and myths about “perfect eyes.”
Astigmatism prescriptions
Cylinder, axis, and plus/minus-cylinder notation education.
Astigmatism on Your Glasses Prescription
Astigmatism on a glasses Rx shows up mainly through cylinder and axis. Learn educational basics without converting CYL into a Snellen score.
Cylinder Explained on Glasses Prescriptions
Deep-dive education on CYL as astigmatic spectacle power: pairing with axis, magnitude myths, and acuity independence.
Axis Explained on Glasses Prescriptions
Axis orients cylindrical correction in degrees. Learn why axis is direction—not severity—and how it pairs with CYL.
Minus-Cylinder Notation Explained
Educational guide to minus-cylinder spectacle notation: how written SPH/CYL/AXIS appear and why transposition confuses patients.
Plus-Cylinder Notation Explained
Educational guide to plus-cylinder spectacle notation and how it relates to minus-cylinder form after transposition.
Prescription Transposition Education
Learn what plus/minus cylinder transposition means educationally—why numbers reshuffle and why you should not DIY transpose for orders.
Why Axis Can Change Between Exams
Educational reasons axis may differ between visits: true change, measurement variability, and notation—without panic scripts.
Pupillary distance (PD)
Single vs dual PD, distance vs near PD, and measurement basics.
Single PD vs Dual PD
Single (binocular) PD is one total number; dual (monocular) PDs split right and left. Learn when each matters for lens centration.
How to Measure PD (Educational)
Professional measurement with a pupillometer or calibrated digital system is preferred, especially for progressives and higher powers. Home methods are rough educational exercises.
Average Pupillary Distance
Average PD charts are statistical summaries, not your face. Learn why averages mislead ordering and when professional measurement matters.
Near PD vs Distance PD
Distance PD and near PD differ because fixation distance changes geometry. Learn why progressives and near work make the distinction educationally important.
Prescription strength questions
Educational pages about common sphere magnitudes and “how strong” questions — without equating diopters to acuity.
-0.50 Sphere Prescription Explained
Educational guide to a -0.50 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-1.00 Sphere Prescription Explained
Educational guide to a -1.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-1.50 Sphere Prescription Explained
Educational guide to a -1.50 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-2.00 Sphere Prescription Explained
Educational guide to a -2.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-2.50 Sphere Prescription Explained
Educational guide to a -2.50 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-3.00 Sphere Prescription Explained
Educational guide to a -3.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-4.00 Sphere Prescription Explained
Educational guide to a -4.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-5.00 Sphere Prescription Explained
Educational guide to a -5.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
-6.00 Sphere Prescription Explained
Educational guide to a -6.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
+0.50 Sphere Prescription Explained
Educational guide to a +0.50 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
+1.00 Sphere Prescription Explained
Educational guide to a +1.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
+1.50 Sphere Prescription Explained
Educational guide to a +1.50 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
+2.00 Sphere Prescription Explained
Educational guide to a +2.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
+2.50 Sphere Prescription Explained
Educational guide to a +2.50 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
+3.00 Sphere Prescription Explained
Educational guide to a +3.00 D spherical glasses prescription value — not an acuity conversion and not a diagnosis.
Is -1.00 Eyesight Bad?
-1.00 D sphere is a mild minus sphere example. It is not a verdict on eye health. Do not convert -1.00 to a guaranteed Snellen fraction.
Is -2.00 Eyesight Bad?
-2.00 D sphere is a moderate minus sphere example. It is not a verdict on eye health. Do not convert -2.00 to a guaranteed Snellen fraction.
Is -3.00 Eyesight Bad?
-3.00 D sphere is a noticeable minus sphere example in consumer talk. It is not a verdict on eye health. Do not convert -3.00 to a guaranteed Snellen fraction.
What Is Considered a Strong Glasses Prescription?
“Strong” is informal. Learn how to think about higher diopter magnitudes without fake Snellen conversions or fear marketing.
What Does 0.00 Mean on an Eye Prescription?
0.00 usually means no spherical powered correction in that field—educational nuances for plano-like values and neighbors on the form.
What Does Plano Mean on an Eye Prescription?
Plano means no spherical powered correction in that field. Learn how PL relates to 0.00, balance lenses, and myths.
What Does 180 Axis Mean?
Axis 180° (or 0/180 depending on convention) orients cylindrical power horizontally in common teaching—direction, not severity.
Does Higher Cylinder Mean Worse Astigmatism?
Higher CYL means more cylindrical spectacle power was prescribed—not a complete severity or disease verdict by itself.
Can Eye Prescriptions Improve?
Prescriptions can change in more than one direction across life. Learn educational patterns without promising DIY improvement.
Why Did My Prescription Change?
Educational reasons prescriptions change: true refractive shifts, notation, tasks, and eye health—without panic defaults.
Can OD and OS Have Different Prescriptions?
Yes—eyes often differ. Learn why anisometropia appears on Rxs and what to ask about comfort and acuity.
What Does ADD Mean on a Glasses Prescription?
ADD is near addition for multifocals. Learn how it differs from drugstore readers and from distance sphere.
Glasses vs contacts & prescription rights
Why spectacle and contact prescriptions differ, and U.S. consumer prescription-release basics.
Glasses Prescription vs Contact Lens Prescription
Glasses and contact lens prescriptions are not interchangeable. Learn why vertex distance, fitting parameters, and regulations differ—educational, not a fitting guide.
US Eyeglass Prescription Release (Educational)
Educational overview of U.S. eyeglass prescription release concepts under the FTC Eyeglass Rule—not legal advice for your dispute.
More guides
Additional related educational pages.
