Enter your prescription values from your eye exam report. All fields are optional — enter what you have.
OD — Right Eye
D
Nearsighted: negative | Farsighted: positive
D
Astigmatism correction (usually negative)
°
1–180° — direction of astigmatism
D
For bifocals / progressives (age 40+)
OS — Left Eye
D
D
°
D
Overall Prescription Strength
—
⚠ Medical Disclaimer: This tool is for educational purposes only. Always consult a licensed optometrist or ophthalmologist for your prescription needs. Do not order glasses without a valid, current prescription.
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Understanding Your Eye Prescription
An eyeglass prescription contains several values that together describe your vision correction needs. Each value has a specific meaning — once you understand them, your prescription becomes much easier to read.
Prescription Values Explained
SPH (Sphere) — Overall lens power in diopters (D)
Negative values (-) = myopia (nearsightedness). Positive values (+) = hyperopia (farsightedness). Zero = no sphere correction needed. Values beyond ±6.00 are considered high prescriptions.
CYL (Cylinder) + AXIS — Astigmatism correction
CYL measures the degree of astigmatism. AXIS (1–180°) tells the lens maker the orientation. If CYL is blank, you have no significant astigmatism. CYL values over ±2.00 are considered moderate to high.
ADD — Near addition for presbyopia (bifocals/progressives)
ADD is always positive and is added to the distance SPH to get the reading prescription. Typical ADD range: +0.75 to +3.50. Your reading SPH = Distance SPH + ADD.
💡 OD vs OS: OD = Oculus Dexter (right eye). OS = Oculus Sinister (left eye). OU = Oculus Uterque (both eyes). These are Latin abbreviations still used in optometry worldwide.
Frequently Asked Questions
A negative SPH value (e.g., -2.50) means you are myopic (nearsighted) — you can see close objects clearly but distant objects appear blurry. The larger the negative number, the stronger the correction needed. -1.00 to -3.00 is mild myopia; -3.00 to -6.00 is moderate; beyond -6.00 is high myopia.
SPH corrects for overall refractive error (nearsightedness or farsightedness) uniformly across the lens. CYL corrects for astigmatism — where the eye is shaped more like a football than a sphere — and is directional, requiring an AXIS value to specify orientation. A prescription can have SPH only, CYL only, or both.
If you have an ADD value, your reading prescription = Distance SPH + ADD. For example: OD -2.00 ADD +2.00 → Reading OD = +0.00 (plano). OS -1.50 ADD +2.00 → Reading OS = +0.50. The CYL and AXIS remain the same for both distance and reading. You do NOT need a separate exam for reading-only glasses if you have an ADD value.
Not directly. Contact lens prescriptions include additional measurements: base curve (BC), diameter (DIA), and brand. Contacts sit on the eye rather than in front of it, so the power is often slightly different. A contact lens fitting exam is required separately. Generally, the SPH is adjusted slightly for contacts due to the shorter vertex distance.
Adults should have a comprehensive eye exam every 1–2 years. Prescriptions can change gradually and wearing outdated glasses can cause eyestrain and headaches. Children and teens should be examined annually as their prescriptions often change faster. In the US, prescriptions expire after 1–2 years depending on state law.
Sphere (SPH) corrects nearsightedness/farsightedness — the base lens power. Cylinder (CYL) corrects astigmatism from an irregular cornea. Axis (0°–180°) specifies the cylinder's orientation. A prescription of -2.50 -1.25 × 090 means: -2.50 diopters of nearsighted correction, -1.25 diopters of astigmatism correction, oriented at 90 degrees.
The "Add" (Addition) is extra magnifying power for the reading zone of progressive or bifocal lenses, typically +0.75 to +3.00 diopters. It compensates for presbyopia — the age-related near-focus loss starting in the mid-40s. The Add is the same for both eyes. Single-vision reading glasses use Distance SPH + Add as their total power.
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