Why a toric lens must be considered in every cataract operation

“I only have a small astigmatism in my glasses, so I don’t need a toric lens” — this is one of the most common wrong conclusions before cataract surgery. Paradoxically, in some patients astigmatism can be greater after surgery than before it — if nobody measured precisely where that astigmatism comes from before the operation. We explain why this happens.

Astigmatism is not one thing — it has two sources

Astigmatism is a refractive error in which the eye does not focus light at a single point because its optical system is not perfectly symmetrical. The image becomes blurred or distorted regardless of distance. Importantly, the total astigmatism of the eye is made up of two components:

Corneal astigmatism — results from the uneven curvature of the cornea, which instead of a section of a sphere resembles a section of a rugby ball. This component is permanent: it does not disappear after cataract surgery.

Lenticular (internal) astigmatism — comes from the natural lens of the eye: its shape, its position and, with age, uneven cataractous opacities.

Glasses and the result of a refraction test correct the sum of both components. And this is where the problem begins.

The lens can mask corneal astigmatism

In many people lenticular astigmatism has an axis opposite to the corneal one — the components partly cancel each other out. A patient may have, say, 2.0 dioptres of corneal astigmatism but wear a cylindrical correction of only 0.5 dioptres in their glasses, because the rest is “fixed” by their own lens.

During cataract surgery the natural lens is removed — and with it the entire lenticular component, including the beneficial part. Pure corneal astigmatism remains. If we implant a standard (non-toric) lens, the patient with a “small 0.5-dioptre astigmatism” wakes up after surgery with 2.0 dioptres of astigmatism — four times more than before the operation. The cataract is gone, but vision without glasses can be disappointing.

The conclusion: the cornea matters, not the glasses

Whether a toric lens is needed is not decided by the spectacle prescription but by measuring the cornea itself. That is why the following are essential before qualification for surgery:

• keratometry and optical biometry — measurement of corneal curvature and the eye’s parameters,
• corneal topography — a map of its shape that also detects irregular astigmatism,
• aberration analysis — an assessment of how the eye’s optical system really behaves.

On this basis we know how much astigmatism will remain after the lens is removed — and whether it is worth correcting it with a toric lens.

How does a toric lens work?

A toric lens has different power in two perpendicular axes — like a cylindrical spectacle lens, but implanted permanently inside the eye. During surgery the surgeon positions it precisely in the calculated axis. A correctly chosen and positioned toric lens neutralises corneal astigmatism, giving sharp vision without cylinders in glasses.

Toric versions exist for every type of lens — monofocal, EDOF and trifocal — so correcting astigmatism does not rule out freeing yourself from reading glasses at the same time.

How does it work at OKUMED?

At our clinic in Gdynia every patient qualified for cataract surgery or RLE undergoes full corneal diagnostics and biometry. The implant-selection consultation takes into account both components of astigmatism and the aberrations of the eye — so that the decision about a toric lens is based on measurements, not on a spectacle prescription from years ago.

Book a qualification consultation at OKUMED — Świętojańska 135/2, Gdynia, phone +48 882 650 299 or via ZnanyLekarz.