What does SPH mean on a prescription?

SPH (Sphere) indicates the amount of lens power to correct nearsightedness (minus) or farsightedness (plus).

What is the difference between plus and minus cylinder notation?

Plus cylinder is used by some optometrists while minus cylinder is more common. They represent the same correction mathematically but with different SPH and CYL values.

Refractive Error Calculator - Prescription Converter

👁️ Right Eye (OD)

SPH (D)

CYL (D)

AXIS (°)

👁️ Left Eye (OS)

SPH (D)

CYL (D)

AXIS (°)

Current Notation

⚠️ For educational purposes only. Always consult your eye care professional.

📖 Understanding Your Prescription

SPH (Sphere): The main lens power. Negative (-) for nearsightedness (myopia), positive (+) for farsightedness (hyperopia).

CYL (Cylinder): The amount of astigmatism correction. Measures the lens power needed for uneven corneal curvature.

AXIS: The angle (1-180°) at which the cylinder power is placed. Indicates the orientation of astigmatism.

Minus Cylinder: Most common notation. The cylinder power is negative and combined with sphere to get total power.

Plus Cylinder: Alternative notation. The cylinder power is positive. The mathematical relationship: SPH(+cyl) = SPH(-cyl) + CYL(-cyl), and CYL(+cyl) = -CYL(-cyl).

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👁️ Right Eye (OD)

👁️ Left Eye (OS)

📖 Understanding Your Prescription