Short answer
Cyl (cylinder) on your prescription measures astigmatism — the amount of corneal or lens irregularity that causes blurred or distorted vision at all distances. It is written in dioptres (D), usually with a minus sign (e.g. −1.75), alongside an Axis (1°–180°) showing orientation. A blank or zero Cyl means no significant astigmatism.
Sph, Cyl, and Axis explained
Your glasses or contact lens prescription has three main fields for each eye: Sph (sphere), Cyl (cylinder), and Axis.
| Field | What it measures | Example | Sign |
|---|---|---|---|
| Sph (Sphere) | Overall focusing error — myopia or hyperopia | −3.50 or +2.00 | Minus (−) = short-sighted · Plus (+) = long-sighted |
| Cyl (Cylinder) | Astigmatism strength in dioptres | −1.75 | Usually minus in UK/EU prescriptions |
| Axis | Orientation of astigmatism | 85 | 1° to 180° — no plus or minus sign |
How to read a full prescription
−3.50 / −1.75 × 85 means −3.50 D myopia, −1.75 D astigmatism, with the cylinder oriented at 85°. All three numbers describe one eye — left and right may differ.
The slash or space separates Sph from Cyl; the × (or x) introduces the Axis. Some prescriptions write DS (dioptres sphere) when Cyl is blank — meaning no astigmatism correction needed for that eye.
What do different Cyl values mean?
| Cyl value | Level | Typical symptoms | Treatment if you want freedom from glasses |
|---|---|---|---|
| −0.25 to −0.75 D | Low | Mild blur — may not need correction | LASIK if bothersome |
| −0.75 to −1.5 D | Mild | Noticeable smear, night starbursts | LASIK · SMILE Pro |
| −1.5 to −3.0 D | Moderate | Clear distortion at all distances | LASIK · SMILE · toric ICL |
| −3.0 to −5.0 D | High | Strong directional blur, poor night driving | LASIK or toric ICL |
| Above −5.0 D | Very high | Severe distortion — topography essential | Toric ICL preferred |
What if Cyl is blank or zero?
No significant astigmatism — your blur is from Sph alone (pure myopia or hyperopia). You only need sphere correction in glasses or laser planning.
Very low Cyl (e.g. −0.25) may be omitted on some prescriptions if the optometrist considers it clinically insignificant. Only an eye test confirms what your eyes actually need.
Why do I need toric glasses or contacts?
Standard spherical lenses only correct Sph. Any Cyl value requires a toric lens — shaped to counteract astigmatism at the correct Axis. Toric contacts must stay aligned; rotation causes intermittent blur.
Many people with Cyl on their prescription seek laser surgery because toric contacts are fiddly and glasses feel never quite sharp enough. Read: Can LASIK fix astigmatism?
Does Cyl always mean keratoconus?
No. Most Cyl values indicate regular, stable astigmatism — highly correctable. Keratoconus causes irregular, progressive astigmatism detected on corneal topography, not from the Cyl number alone.
Compare: Astigmatism vs keratoconus · Return to astigmatism prescription section.
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Related: Astigmatism guide · Can LASIK fix astigmatism? · Myopia vs astigmatism