THE CLEAR VISION GUIDE

Understand your glasses prescription

Learn what SPH, CYL, AXIS, ADD, PD and prism mean with a clearly labelled example and a plain-language glossary.

EXAMPLE ONLY · NOT A PRESCRIPTION

Example of minus-cylinder notation
Eye	SPH	CYL	AXIS	PD
Right / OD	−4.00 D	−0.50 D	180°	31 mm
Left / OS	−3.75 D	−0.75 D	170°	32 mm

PD in this example is recorded separately for each eye. This demonstration must not be used to order lenses.

SPH

Sphere

The spherical lens power, written in dioptres (D). Keep the plus or minus sign exactly as prescribed.

CYL

The cylinder power used to correct astigmatism. Different notation conventions exist; do not change the sign on its own.

AXIS

The orientation of cylinder correction, expressed in degrees. It is an angle, not an additional lens power.

ADD

Additional plus power for near tasks when prescribed. It should be interpreted with the rest of the prescription.

A fitting distance in millimetres. It may be written as a total or separately for each eye; ask which format is used.

PRISM

Prescribed prism includes an amount and a base direction. Keep both and ask the prescriber to explain their purpose.

Sources checked: 2026-09-20