Glasses and contact lens prescriptions are not interchangeable. Both describe vision correction, but a contact prescription also identifies the fitted lens product and its relevant specifications. Optical powers may differ because glasses sit away from the eye; fit, design and product availability also affect the final contact prescription.
What appears on each prescription?
Scroll the table to read every column.
| Field | Glasses prescription or dispensing record | Contact lens prescription / product |
|---|---|---|
| SPH / PWR | Spherical power | Spherical power; may differ after vertex adjustment and fitting |
| CYL and AXIS | When astigmatism correction is prescribed | On toric designs when prescribed; not on every spherical lens |
| ADD | When a near addition is prescribed | Multifocal designs when prescribed; may use product-specific categories |
| BC and DIA | Not contact-fitting specifications on a glasses order | Base curve/designation and diameter, as applicable to the fitted product |
| Manufacturer / brand | Frame and spectacle lens selection are separate | The prescribed contact lens product matters |
| PD and prism | PD is used for spectacle centration; prescribed prism may also appear | Routine soft contact orders do not copy spectacle PD or prism; specialty needs require assessment |
The FDA lists contact prescription requirements, including manufacturer/material, power, base curve or designation and diameter when appropriate. A package label identifies a product; it is not a complete patient prescription.
How to Read a Contact Lens Prescription and Lens Box
Start with the eye and exact product name. Then match the fields that apply to that design. Do not fill an empty field with an assumed value or choose a different brand just because the numbers look close.
Scroll the table to read every column.
| Abbreviation | What it means | How to read it |
|---|---|---|
| OD / OS / OU | Right eye / left eye / both eyes | Keep each eye’s parameters together; OU is used only when the record specifies both |
| SPH / PWR / D | Spherical power in diopters | Preserve the plus or minus sign; PL/plano means zero spherical power |
| BC | Base curve or design designation | Usually a radius in millimeters; it is not power |
| DIA | Diameter | Overall lens diameter in millimeters |
| CYL | Cylinder power | Toric astigmatism correction when present; a spherical lens need not have this field |
| AXIS | Cylinder orientation in degrees | Goes with the toric CYL; do not invent an axis when it is absent |
| ADD | Near addition for a multifocal design | May be numeric or LOW/MED/HIGH; categories are specific to the product |
| EXP and LOT on the package | Use-by date and batch identifier | Neither is the prescription’s expiration date |
The ACUVUE prescription-reading guide explains eye, power, curvature, diameter and ADD fields. Products use different labeling formats; ask the dispensing provider about an unclear abbreviation.
Illustrative reading example, not an order or recommendation: a record marked OD, PWR -3.00, BC 8.6 and DIA 14.2 means right eye, minus 3.00 diopters, a stated 8.6 mm curve and 14.2 mm diameter for the named product. A toric row would also specify its CYL and AXIS. Without the exact product and valid prescription, those four values are not enough to select a lens.
For why matching BC does not make two brands equivalent, see base curve and contact lens fitting. For the separate date checks on the packaging and prescription, see EXP, opened-lens replacement and prescription expiry.
Why does vertex distance change the power?
Glasses sit in front of the cornea; contacts sit at the eye. At a stated 12 mm vertex distance, the theoretical glasses-to-contacts formula is F / (1 – 0.012 × F). A minus power becomes less negative; a plus power becomes more positive.
Scroll the table to read every column.
| Spectacle input, 12 mm | Raw theoretical corneal-plane power | Site’s 0.25 D display |
|---|---|---|
| -5.00 D | -4.71698 D | -4.75 D |
| +6.00 D | +6.46552 D | +6.50 D |
These are optical examples, not product selections. Use the two-way vertex calculator to compare theoretical powers: choose Glasses → Contacts or Contacts → Glasses and enter the corresponding input power. The reverse equation is an optical equivalent, not a new glasses prescription. For a spherical reference, use the 12 mm vertex conversion chart. Astigmatic inputs require separate meridian calculations in the toric conversion tool.
Does fitting require a separate appointment?
Contact lens fitting is a distinct service from spectacle refraction, but it can be provided during the same appointment or through additional visits. A separate service does not always mean a separate visit. Ask the practice what its package includes, including trial lenses and follow-up; use the exam and fitting cost guide to avoid counting an included service twice.
Your prescriber determines the final contact lens specification after the appropriate assessment. In the U.S., the FTC requires a prescription copy when fitting is complete. A calculator result, a lens box or a glasses prescription does not replace that fitted contact prescription.
