Why it exists
A normal cornea is spherical: it bends light in the same way in every direction. An astigmatic cornea is more steeply curved along one axis than the other, like a rugby ball. Light rays no longer meet at one point but at two, and the image is stretched or doubled.
Removing the natural lens does nothing to change this geometry: the astigmatism lies in the cornea, so it remains after the operation. Without correction, a patient with astigmatism who has cataract surgery sees blurred both far and near, and wears glasses all the time.
How it works
A toric lens has a different power along two perpendicular axes. It exactly offsets the uneven curvature of the cornea, provided it is positioned along the precise axis of your astigmatism.
This axis is measured before the operation by corneal topography, and the lens is rotated into place to within a degree as it is implanted. A ten-degree misalignment loses about a third of the corrective effect, which is why this step calls for such care.
How much astigmatism is worth correcting
Below about one dioptre, astigmatism causes little trouble and does not justify the extra charge. Above that, correcting it makes a real difference to how you see. The pre-operative assessment decides: what counts is the value measured by topography, not the one on your glasses prescription, which also includes the part due to the natural lens.
What you should know
- Toric correction can be added to every lens family: there are toric monofocal, toric EDOF and toric multifocal lenses.
- The extra charge is not covered by French national health insurance (Assurance Maladie). A top-up health insurance policy (mutuelle) may cover all or part of it.
- Later rotation of the lens within the capsular bag can happen. It is rare, and may require the lens to be repositioned.
- The correction applies to regular astigmatism. Irregular astigmatism, caused for example by keratoconus or a corneal scar, needs a different approach.
The alternative
Mild astigmatism can also be treated with corneal relaxing incisions made during the operation. The result is less precise and less stable than with a toric lens, but the option exists and we can discuss it at your consultation.
Toric correction across the four lens families
Same principle, with astigmatism correction added. Its axis must be aligned precisely.
The intermediate-distance comfort of the Monofocal Plus, combined with astigmatism correction.
Extended depth of focus, combined with astigmatism correction.
Every distance, plus astigmatism correction. Of all four, this lens needs the most precise alignment.
Clear vision without glasses Variable comfort Glasses needed Toric axis marks
The two gold marks show the axis of the lens, which must line up with the axis of your astigmatism. A ten-degree misalignment loses about a third of the corrective effect, hence the care this step requires.
Dr Emmanuel Halimi
Ophthalmic surgeon · RPPS 10100555084 · Medical Council of Hauts-de-Seine no. 92/23003
Page written and approved by the surgeon.
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