How to Read Your Eyeglass Prescription (Rx)
An optical prescription is a standardized medical document issued by an optometrist (OD) or ophthalmologist (MD) specifying the exact corrective lens parameters required for clear and comfortable vision.
Entering your prescription details accurately ensures your custom lenses are crafted with optical precision. Refer to the comprehensive glossary and parameter guide below to interpret your prescription before placing your order.
Key Prescription Abbreviations
| Parameter | Term | Definition & Clinical Purpose | Typical Values |
|---|---|---|---|
| OD | Oculus Dexter | The medical designation for your Right Eye. | — |
| OS | Oculus Sinister | The medical designation for your Left Eye. | — |
| OU | Oculus Uterque | Refers to Both Eyes (used when values apply equally to each eye). | — |
| SPH | Sphere | Primary refractive correction power. Indicates the degree of nearsightedness (Myopia) or farsightedness (Hyperopia). | Measured in quarter-diopters (e.g., -2.25, +1.50). |
| CYL | Cylinder | Corrective lens power required to compensate for corneal curvature irregularities (Astigmatism). | Negative (-) or positive (+) diopters. |
| AXIS | Axis | Orientation angle of the astigmatic cylindrical correction on the lens plane. | Integer between 1° and 180°. |
| ADD | Near Addition | Additional magnifying power required for reading or close-up focus in multifocal (bifocal or progressive) lenses. | Positive values (e.g., +1.00 to +3.00), almost always identical for both eyes. |
| PRISM | Prismatic Power | Optical lens deviation prescribed to correct binocular alignment conditions, such as diplopia (double vision). | Numerical value paired with a base direction (BU, BD, BI, BO). |
In-Depth Parameter Breakdown
1. SPH (Sphere)
— Negative (-) Values: Indicate Myopia (nearsightedness), meaning distant objects appear blurred.
— Positive (+) Values: Indicate Hyperopia (farsightedness), meaning nearby objects require extra refractive accommodation.
— Plano / "PL" / "0.00": Indicates no spherical correction is needed (zero diopters of refractive error). Select 0.00 during checkout.
2. CYL & AXIS (Astigmatism Correction)
— Direct Dependency: A CYL value cannot exist without an AXIS value, and vice versa. They operate as a functional pair.
— Absence of Astigmatism: If your prescription states "DS" (Diopter Sphere), "SPH", or leaves the CYL column blank, you do not have astigmatism in that eye. Select 0.00 or None for both CYL and Axis.
— Axis Coordinate: Indicates the precise angular meridian of the cylinder, ranging strictly from 1 to 180 degrees. It does not denote lens thickness or strength.
3. ADD (Near Addition / NV-ADD)
— Frequently listed as ADD or NV-ADD (Near Vision Addition).
— This parameter is only necessary if you are purchasing Progressive, Bifocal, or Dedicated Reading Glasses. If you are purchasing single-vision distance glasses, leave this field blank.
4. Prism & Base Orientation
Prism is an advanced optical correction and is rarely prescribed. If not explicitly recorded on your prescription slip, do not add prism values, as unprescribed prism will induce eyestrain and visual distortion.
When prism is present, each value is accompanied by a directional base orientation:
• BU: Base Up
• BD: Base Down
• BI: Base In (toward the bridge of the nose)
• BO: Base Out (toward the ear/temple)
Critical Reminders Before You Submit
Eyeglass Rx vs. Contact Lens Rx:
Eyeglass prescriptions and contact lens prescriptions are not interchangeable. Contact lenses sit directly on the cornea, altering the required optical vertex distance and cylinder parameters. Always use a prescription specifically intended for spectacles.
Quarter-Diopter Increments:
SPH and CYL values strictly increase or decrease in steps of 0.25 diopters (e.g., 0.25, 0.50, 0.75, 1.00). An Axis value, however, is always an integer from 1 to 180.
Pupillary Distance (PD):
To finalize your custom lenses, you will also need your Pupillary Distance (PD)—the measurement in millimeters between the centers of your pupils. If your doctor did not write your PD on your prescription, consult our PD Measurement Guide to measure it accurately at home.
Still Unsure About Your Numbers?
Upload a photo or scanned copy of your official prescription slip during checkout, and our licensed optical specialists will review and verify your values before lab production begins.