How to Read Your Eye Prescription: SPH, CYL, Axis, and Everything Else Explained

作者: 发布时间: 2026-08-14 11:29:06 查看数: 6

Your doctor hands you a prescription card, and it looks like a row of numbers and abbreviations that mean nothing at a glance. That card is everything you need to order prescription glasses online, but only if you know what each field actually means. The numbers are straightforward once you know the logic behind them.

Quick Reference: Your Prescription at a Glance

Field	What It Means	Example	How to Read It
OD	Right eye (oculus dexter)	OD: -2.00	Your right eye needs a -2.00 SPH lens
OS	Left eye (oculus sinister)	OS: -1.75	Your left eye needs a -1.75 SPH lens
SPH	Lens power to correct nearsight or farsight	-2.00 / +1.50	– = nearsighted; + = farsighted; higher number = stronger
CYL	Astigmatism correction strength	-0.75	Blank = no astigmatism; any value = correction needed
Axis	Direction of astigmatism (1–180°)	090	Only appears with CYL; copy exactly as written
ADD	Extra reading power for bifocals/progressives	+2.00	Always positive; applies to the reading zone of the lens
PD	Distance between pupils in mm	63 / 31/32	Single number = both eyes; two numbers = right/left separately
Prism	Corrects eye alignment issues	1.5 BU	Number = strength; BU/BD/BI/BO = direction of correction

What Is SPH?

SPH stands for sphere. It tells you how strong your lenses need to be to bring your vision into focus, and whether you are nearsighted or farsighted.

How to Read the Sign

● Minus (–) means nearsighted (myopia). You can see close up but struggle with distance. Nearsighted glasses carry a negative SPH value.

● Plus (+) means farsighted (hyperopia). You see better at a distance but struggle up close.

How to Read the Number

The number is measured in diopters (D), increasing in 0.25 steps. The further from zero, the stronger the prescription.

SPH Value	What It Means
0.00 to –1.00	Mild nearsightedness
–1.25 to –3.00	Moderate nearsightedness
–3.25 to –6.00	High nearsightedness
–6.00 and above	Very high nearsightedness
+0.25 and above	Farsightedness

If your SPH field says pl or plano, it means zero, no correction needed in that eye for distance.

What Is CYL?

CYL stands for cylinder. It measures the degree of astigmatism in your eye, which happens when the cornea or lens is not perfectly round.

A CYL value on your glasses prescription means your lenses need an extra curve in a specific direction to correct blurry or distorted vision. Not everyone has astigmatism. If your CYL field is blank or reads 0.00, your eyes are symmetrical enough that no astigmatism correction is needed.

Positive vs. Negative CYL

Prescriptions can be written in two formats: minus cylinder (most common in the US) or plus cylinder (used in some other countries). The two formats describe the same correction differently. If you are ordering astigmatism glasses online, use the format written on your prescription without converting it.

CYL Always Comes with an Axis

CYL on its own is not enough. The lens needs to know not just how much correction to apply, but in which direction. That is what Axis does.

What Is Axis?

Axis tells the lab where to position the cylinder correction on your lens. It is a number from 1 to 180, representing degrees of orientation.

Axis only appears when CYL has a value. If your CYL is blank, Axis will be blank too.

What the Numbers Mean

The Axis number does not indicate severity. An Axis of 180 is not worse than an Axis of 45. It simply tells the lens maker which angle to cut the astigmatism correction at.