How to Read Eye Prescription Numbers: Chart and Examples

Key Takeaways

• OD means right eye; OS means left eye. Read each row separately before interpreting the lens numbers or entering an order.
• SPH uses diopters (D) to describe spherical power; minus and plus signs matter. CYL and AXIS work together for astigmatism correction.
• AXIS runs from 1° to 180°, but a larger axis number does not mean more severe astigmatism. CYL describes the cylinder power.
• ADD specifies extra near power; PD is a millimeter fitting measurement. Neither should be guessed from other numbers on the prescription.

To read an eye prescription, locate the right-eye and left-eye rows, check the sign and value of SPH, read CYL together with AXIS, and then look for ADD, prism, and pupillary distance (PD). You do not need to diagnose your eyesight to understand what each field tells the lens maker.

An eyeglass prescription is a set of optical instructions, not a report card for how well someone sees. The familiar abbreviations become easier to follow when the correction and fitting information are treated as different kinds of measurements.

An eyeglass prescription records the corrective lens parameters determined during a refraction. OD and OS identify the right and left eyes; sphere (SPH) and cylinder (CYL) express optical power in diopters; axis specifies astigmatism orientation in degrees. ADD, prism, and pupillary distance provide additional correction or lens-positioning information when applicable.

The simplest way to use those definitions is to compare a realistic prescription grid with the paper or electronic copy from an eye exam.

Eye Prescription Chart: A Sample You Can Read in Minutes

The following eye prescription chart is fictional. Its purpose is to explain the format used on many U.S. spectacle prescriptions, not to recommend lens powers for a particular person.

Other entries in this made-up example: distance PD = 63 mm, recorded as OD 31 mm / OS 32 mm; prism = not prescribed. The numbers have different units: SPH, CYL, and ADD are powers in diopters; AXIS is an orientation; PD is a physical distance in millimeters.

The right eye needs −2.50 D of spherical correction and −0.75 D of cylinder at axis 090. The left eye uses −1.25 D sphere with −1.00 D cylinder at axis 175. An ADD of +1.75 D is listed for near correction in both eyes. ADD alone does not determine whether the final lenses should be bifocals or progressives; that decision depends on the prescribed lens design and the wearer’s needs.

One detail makes this chart especially useful: the right and left eyes do not have to share the same SPH, CYL, or AXIS values. A prescription can also be printed vertically, or use RE/LE instead of OD/OS. Follow the field labels, not the location of a number on the paper.

How to Read Eye Prescription Numbers: Every Field Explained

OD, OS, and OU: Right Eye, Left Eye, or Both?

OD (oculus dexter) identifies the right eye; OS (oculus sinister) identifies the left eye; OU (oculus uterque) means both eyes. RE and LE are English-language alternatives. OD after a clinician’s name may instead be the Doctor of Optometry credential, so its position matters.

A row labeled OD belongs to the wearer’s right eye, even when someone else is looking directly at the wearer. The existing OD and OS prescription meanings guide expands on these abbreviations and includes a separate reading tool; the grid above is enough for following the examples here.

SPH (Sphere): What Do Plus and Minus Numbers Mean?

SPH is the spherical lens power, measured in diopters (D). A minus value such as −2.00 D is typically used to correct myopia (nearsightedness); a plus value such as +1.50 D commonly corrects hyperopia (farsightedness). A 0.00 or PL (plano) entry denotes no spherical power in that field, not necessarily no prescription at all.

The sign is part of the measurement. −2.50 is not interchangeable with +2.50. The farther a spherical value lies from zero, the greater the spherical lens power specified, but the number does not by itself measure visual acuity or diagnose eye disease.

A printed eyeglass prescription may display SPH as S, Sphere, or Sph. Optical powers commonly appear in quarter-diopter increments, such as −1.25, −1.50, and −1.75. Copy the actual number from the prescription: do not round it because an order form presents a shorter list.

CYL and AXIS: How Does Astigmatism Correction Work?

CYL gives the additional cylindrical lens power used for astigmatism; AXIS states its orientation. A prescription with CYL −0.75 D and AXIS 090 is specifying a paired correction. CYL is not the same kind of value as SPH, and AXIS is not a strength score.

The pairing is technical rather than cosmetic: a cylinder measurement is meaningful only with the orientation at which it acts.

Astigmatism lens correction uses sphere, cylinder, and axis as a linked set of parameters. Sphere and cylinder are measured in diopters; cylinder indicates the difference in lens power between meridians; axis, from 1 to 180 degrees, identifies cylinder orientation. Axis is not a severity scale.

In practice, an axis of 180° is not more powerful than 90°. Larger absolute CYL power means a larger cylindrical component, not necessarily worse day-to-day vision. A prescription may also use plus-cylinder notation rather than the minus-cylinder format shown here; professionals can transpose between equivalent notations, but an online shopper should not perform a casual sign change.

The astigmatism glasses prescription guide explains how the CYL/AXIS pair affects lens selection and why different astigmatism-related terms should not be treated as interchangeable. Enter both values exactly as written on the prescription being used for the order.

ADD: What Is Additional Reading Power?

ADD means additional plus power for near work, often associated with presbyopia and used when a lens design provides more than one viewing distance. A +1.75 D ADD is not a replacement for distance SPH. It is an addition applied to the near portion of a suitable prescription design.

For example, an uncomplicated distance sphere of −2.00 D with +1.50 D ADD corresponds to a near spherical component of −0.50 D before other prescription and lens-design considerations. That arithmetic is an explanation, not a substitute for the optician’s final lens calculation. For prescriptions with cylinder, prism, or specialized designs, do not turn the near addition into a new standalone order yourself.

The lens choice also matters: conventional bifocals contain separate near and distance zones, whereas progressive designs transition through multiple viewing distances. The progressive versus bifocal lenses comparison handles that separate decision after the prescription has been understood.

PD: Single, Dual, and Near Pupillary Distance

PD (pupillary distance) measures pupil positioning in millimeters, not the strength of the glasses. A binocular or single PD may be written as 63 mm. The same distance may appear as two monocular values, for instance OD 31 mm and OS 32 mm, which add to 63 mm.

A single PD should not automatically be halved into equal left and right numbers. Some ordering systems also distinguish distance PD from near PD; the near measurement should not be derived using an assumed fixed subtraction. Precise optical centration can be especially important for stronger prescriptions and multifocal fitting.

Prism, Base Direction, DS, and PL

Prism is a prescribed optical displacement used for selected binocular-vision problems, including some forms of double vision. A prism entry usually contains both an amount, expressed in prism diopters (Δ), and a base direction such as BI (base in), BO (base out), BU (base up), or BD (base down). The base direction is essential and must never be inferred from SPH or AXIS.

DS may mean diopter sphere, indicating no separate cylinder component in that entry. PL or plano means zero spherical power. A dash, blank, or zero can have different meanings across paper and electronic forms, so unclear notation should be confirmed with the prescriber or dispensing optician rather than guessed.

How to Read a Glasses Prescription Step by Step

Return to the sample eye prescription chart and read it as five short checks. The goal is to reproduce a clinician’s written measurements accurately, not to change them.

1. Identify the eye. OD is the right eye; OS is the left eye. Confirm both labels before copying any numbers into a form.
2. Check SPH and its sign. OD is −2.50 D and OS is −1.25 D. Minus signs belong to the prescription, not to the page layout.
3. Keep CYL beside AXIS. OD has CYL −0.75 with axis 090; OS has CYL −1.00 with axis 175. A cylinder value should not be entered with an axis copied from the opposite eye.
4. Find any extra prescribed correction. This example lists ADD +1.75 for both eyes and no prism. Real-world prescriptions may omit ADD and/or include separate prism values.
5. Verify the fitting values separately. The sample distance PD is 63 mm total or 31/32 mm monocular. PD may be measured and supplied outside the main prescription grid.

A patient who still needs a PD can review the measurement formats and calibration steps in this PD measurement before ordering glasses tool. Self-measurement is not appropriate for every lens design; professional fitting may be necessary, especially for prism or progressive prescriptions.

The completed reading is therefore straightforward: two eyes with different spherical and cylindrical correction, two different cylinder orientations, and the same near addition. Nothing in the chart directly states a 20/20 score, guarantees a particular lens material, or identifies an eye disease.

Four Glasses Prescription Examples Explained

Example 1 — Nearsightedness Without Astigmatism

Both eyes have negative SPH values, consistent with spherical correction for nearsightedness. No cylinder correction is recorded, so the axis fields are not used. A person with this fictional prescription would still need the prescribed lens type and relevant fitting measurements before ordering.

Example 2 — Nearsightedness With Astigmatism

The OD row specifies −3.00 D SPH plus −1.25 D CYL at 180°. The OS row specifies −2.25 D SPH plus −0.50 D CYL at 020°. Axis 180 does not imply more severe astigmatism than axis 020; it simply places the correction in a different direction. Do not add SPH and CYL together and type the result into the SPH field. The American Academy of Ophthalmology prescription guide provides the clinical definitions behind this common notation.

Example 3 — A Prescription With ADD for Progressive Lenses

Each eye has a positive distance sphere, a modest cylindrical correction, and a +2.00 D near addition. These fields could be used for a prescribed multifocal design, but the numbers alone do not specify the finished progressive corridor, fitting height, or frame suitability. The wearer and eye-care professional must decide the appropriate lens design.

Example 4 — A Prescription With Prism

The right-eye row includes a prism of 1.0 prism diopter, base out. It would be unsafe to omit BO or to assume the left eye should receive the same prism. This is an illustration of notation, not a clinical recommendation. A prism prescription calls for careful confirmation of the prescribed amount, direction, and optical fitting.

What Do Your Eye Prescription Numbers Say About Your Eyesight?

Is −2.00 a Strong Eye Prescription?

−2.00 D means two diopters of minus spherical lens power. Compared with −0.50 D, it specifies more spherical minus correction; compared with −6.00 D, it specifies less. The value alone cannot tell a reader what line they can see on an eye chart, whether they need glasses for every task, or whether the eye is healthy.

The National Eye Institute lens overview distinguishes single-vision lenses from multifocal designs and explains that eyeglasses correct the way light focuses on the retina. Prescription interpretation is therefore about the lens correction, not a substitute for a comprehensive eye-health examination.

Is AXIS 180 Worse Than AXIS 90?

No. AXIS specifies orientation, and both 180° and 90° are valid directions for a cylinder correction. The CYL entry contains the cylindrical power. The exact axis may be important to clear vision, but it does not rank eyes from good to bad.

Can You Have 0.00 SPH and Still Need Glasses?

Yes. An eye may have plano SPH but a nonzero CYL and AXIS, meaning the spherical component is zero while astigmatism correction is prescribed. Other people may have a near addition or prism correction. An isolated 0.00 field is not a complete assessment of all lens needs.

Is 20/20 Vision the Same as an Eye Prescription?

No. A 20/20 score reports distance visual acuity under test conditions; an eyeglass prescription reports lens parameters. A numerical prescription cannot be converted reliably into a single 20/20-style vision score. Eye-chart performance can also be affected by factors beyond refractive error, so the two measures answer different questions.

How to Read an Eyeglass Prescription Before Ordering Online

The Prescription Entry Checklist

An online order goes wrong most easily when a correct paper prescription is transcribed incorrectly. Before payment, compare the order summary against the original signed or otherwise valid prescription, row by row.

A missing selection in a retailer’s form does not authorize changing the prescription. If a store does not support a prescribed prism, a required lens design, or a specific fitting measurement, pause the order and speak with the retailer or an eye-care professional. Distinct prescriptions written in plus-cylinder and minus-cylinder notation can sometimes describe equivalent optics, but the optical conversion should be handled professionally.

What If Your Prescription Does Not Include PD?

PD may be absent because it is a fitting measurement rather than a universal field on every eyeglass prescription. In the United States, the federal Eyeglass Rule requires automatic prescription release after a refractive exam, but its definition refers to information needed under applicable state law. Some states require PD on the prescription; federal rules do not impose that requirement in every state.

For readers ordering online, the regulatory distinction has a practical consequence: having the prescription and having every fitting measurement needed by a particular seller are not always the same thing.

Under the U.S. Eyeglass Rule (16 CFR Part 456), eye doctors must provide an eyeglass prescription after refraction and before offering glasses for sale. According to the Federal Trade Commission’s final rule published in June 2024, federal requirements do not universally mandate pupillary distance (PD); state rules may differ.

A missing PD therefore does not automatically mean the clinic issued an invalid prescription. The current FTC Eyeglass Rule guidance explains the state-law distinction and encourages eye-care offices that have already measured PD to give that information to patients.

For simple distance spectacles, an at-home PD check can help someone understand the difference between single and monocular measurements. Self-measurement does not replace professional centration or fitting-height measurements when the prescription or lens design requires them, particularly for progressives, prism, or demanding high-power lenses.

Can You Use a Contact Lens Prescription for Glasses?

No. A contact-lens prescription is not interchangeable with an eyeglass prescription, even when the sphere numbers look similar. Contacts sit on the ocular surface and require fitting information that a spectacle prescription ordinarily does not contain.

A prescribed contact-lens product typically includes brand or material, base curve, diameter, and power, plus other specifications when appropriate. A separate fitting visit also checks lens movement, comfort, and the eye’s response to the actual contact lens. Those measurements are not a substitute for the spectacle lens fitting parameters. The FDA contact-lens prescription requirements set out the required information for contact-lens prescriptions.

The correct next step depends on which prescription is missing. A glasses wearer who has only a contact-lens prescription should request a current spectacle prescription from an authorized prescriber. A contact-lens wearer who has only a glasses prescription should obtain a dedicated contact-lens fitting and a valid contact-lens prescription before ordering lenses. The two documents can show similar powers, especially in some low-power prescriptions, but that resemblance does not establish interchangeability.

An optical conversion also is not just a sign or decimal adjustment. A spectacle lens normally sits in front of the eye, whereas a contact lens rests on the tear film. For higher powers, that difference in position can affect effective correction; a proper contact-lens prescription also addresses how the particular lens fits and performs on the eye. Astigmatic contact lenses can involve manufacturer-specific stabilization and orientation requirements. No single online formula can reliably supply all the clinical and product parameters from a glasses prescription.

Keep the two prescriptions separate when entering an order. Lens manufacturers and retailers may use similar terms such as SPH, CYL, and AXIS for both, but the surrounding measurements and fitting process differ. The dedicated glasses versus contact lens prescriptions article explains those differences in greater detail. Never substitute one prescription document for the other or calculate missing contact-lens parameters yourself.

Frequently Asked Questions

What Does a Negative Eye Prescription Mean?

A negative SPH, such as −1.75 D, generally indicates minus spherical correction for nearsightedness. The exact number expresses lens power, not a diagnosis of overall eye health or a guaranteed eye-chart score.

What Does +2.00 ADD Mean on a Glasses Prescription?

ADD +2.00 means an extra +2.00 D near addition is prescribed on top of the relevant distance correction for an appropriate near or multifocal design. It should not be entered as distance SPH or assumed to be an over-the-counter reader strength.

Does a Higher AXIS Number Mean Worse Astigmatism?

No. AXIS values from 1° through 180° indicate the direction of cylinder correction. Cylinder magnitude, other prescription parameters, and actual visual performance are different questions.

Why Is PD Missing From My Eye Prescription?

PD may be recorded separately as a fitting measurement. Federal U.S. rules do not automatically require its inclusion in every state, although certain state requirements differ. Ask the prescriber or optician for an accurate PD measurement when needed for lens ordering.

Can a Glasses Prescription Expire?

Yes. Prescription expiration and validity requirements depend on the jurisdiction and prescription details. Check the issue and expiry information on the prescription and the applicable state rules rather than assuming every eyeglass prescription has the same lifetime.

Can an Eye Chart Tell Me My Glasses Prescription?

No. A distance visual-acuity chart measures how clearly a person resolves standardized symbols under specific conditions. A refraction determines the optical powers and axes required for a spectacle prescription; an eye chart alone cannot supply the full SPH/CYL/AXIS/ADD information.

Bottom Line

Reading a glasses prescription is mainly an exercise in separating eye labels, lens powers, orientation, and fitting measurements. Identify OD and OS, preserve the SPH and CYL signs, keep CYL paired with AXIS, and check every extra field required for the actual lenses. Use the prescribed numbers, not the teaching examples in this guide, and ask an eye-care professional to resolve unclear or missing entries.

This article explains prescription notation for general education. It does not replace an eye exam, individualized medical advice, or professional lens dispensing.