Learn · Your prescription, number by number

What does CYL mean on your prescription?

CYL — cylinder — is your astigmatism correction: how much extra power the lens adds along one direction to even out a cornea that is not perfectly round. It never appears alone; it always has an axis beside it.

THE ANATOMY OF A PRESCRIPTION

	SPH	CYL	AXIS	ADD
OD	−2.25	−0.75	175	+0.75
OS	−2.75	−0.50	12	+0.75

PD 62 mm · Progressive lenses

Astigmatism, in one sentence

A perfectly shaped cornea is a slice of a sphere, like a football cut in half. Most corneas are slightly closer to a rugby ball — a little steeper in one direction than the other — so light focuses at two different distances instead of one point. That is astigmatism, and the cylinder is the correction that pulls the two back together.

It is extremely common, and usually small

Some cylinder shows up in a majority of prescriptions. Rough bands:

Under −0.75 D — mild. Very common; often barely noticeable uncorrected.
−0.75 to −1.50 D — moderate. Uncorrected, fine detail softens and night-time lights start to streak.
Beyond −1.50 D — significant. Lines can look stretched or doubled, and the correction makes an obvious difference.

Minus or plus cylinder? The same correction can be written two mathematically equivalent ways — a fact that confuses many people comparing an old prescription against a new one. European optometry usually writes minus cylinder; some ophthalmology notation writes plus. −2.25 −0.75 × 175 and −3.00 +0.75 × 85 are the same lens. If two prescriptions look wildly different, check the convention before assuming your eyes changed.

Astigmatism is usually stable — but the axis can drift

The amount of cylinder tends to change slowly in adults. What moves more often is its orientation, and a rotating axis with steady cylinder can leave a lens feeling subtly wrong even though the numbers look similar. This is one of the clearest cases where having the previous prescriptions in front of you beats measuring again from scratch.

Does astigmatism mean contact lenses are out?

No. Toric soft lenses correct cylinder routinely; they are weighted so they settle at a consistent rotation on the eye. Your contact-lens prescription will not have the same numbers as your glasses — it is a different distance from the eye — which is why it is worth keeping both.

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