Astigmatism

Astigmatism means that the refractive power differs from one direction (meridian) to another, so light focuses on several focal lines, producing ghosting or smeared images.

Key Facts

• Cause: uneven curvature of the cornea or the lens.
• Symptoms: vision may be blurry both at near and far, with noticeable glare and starbursts at night.
• Correction: cylindrical lenses (with an axis) in glasses or contact lenses; for regular astigmatism, orthokeratology lenses can help.

Understanding the Axis

• In a prescription, CYL is the astigmatism power (negative cylinder is common) and AX is the axis (0°-180°).
• The axis marks the direction that has no refractive power; the perpendicular direction carries the cylinder’s power.

Regular astigmatism can be corrected precisely; irregular astigmatism (such as keratoconus) requires specialist intervention and rigid lenses.