Astigmatism:
myths and realities
of laser treatment.

Astigmatism is not a pathology — it is an anatomical characteristic. The cornea, instead of being perfectly spherical like a football, has a slightly oval shape, like a rugby ball. This asymmetry means that light does not converge at a single point on the retina, but at two different focal lines. The result: blurred or distorted vision at all distances, far and near.

In my experience across more than 25,000 procedures, the vast majority of patients present some degree of astigmatism. In many cases, it is the predominant defect. In others, it adds to myopia or hyperopia. The good news is that the laser corrects it with extreme precision — provided it is measured with equal precision.

Myth #1: "Astigmatism cannot be treated with laser"

False. Regular astigmatism — caused by the asymmetric curvature of the cornea — is routinely corrected by the excimer laser. The AMARIS 1050RS reshapes the cornea by removing more tissue in the steeper meridian and less in the flatter one, transforming the surface from toric to spherical. The result is a symmetrical cornea that focuses light at a single point.

Myth #2: "Astigmatism comes back after laser"

Rare. Corneal astigmatism corrected by laser is stable over time. Unlike myopia, where slight regression is possible in the first months, the axis of treated astigmatism does not shift. Stability is confirmed in our ten-year case series with the AMARIS laser. Residual astigmatism can only appear if the initial correction was imprecise — which brings us to the critical point: measurement.

Physiological astigmatism

Astigmatism of 0.25 - 0.75 D is present in the vast majority of eyes. It is a normal anatomical variant — the perfectly spherical cornea is the exception, not the rule. Physiological astigmatism is typically with-the-rule (the vertical meridian is steeper than the horizontal) and contributes to the natural depth of focus of the eye. It does not require surgical correction — on the contrary, in some cases, slight residual with-the-rule astigmatism improves intermediate vision.

Astigmatism and amblyopia: an important note

When high astigmatism is not corrected in childhood — typically above 1.50 - 2.00 D — the brain does not fully develop the ability to interpret images from the affected eye. This condition is called astigmatic amblyopia (or "lazy eye" from astigmatism). The adult patient with astigmatic amblyopia has corrected visual acuity below normal, even with the best glasses.

Laser surgery can correct astigmatism, but cannot correct the amblyopia itself — the limitation is in the brain, not the eye. However, in many adult patients with mild amblyopia, laser correction of astigmatism produces visual improvement greater than expected, probably due to residual neural plasticity. The topic is complex and deserves a dedicated article.

The real problem: measuring the axis precisely

Astigmatism has two parameters: power (how many dioptres) and axis (at how many degrees). A power error blurs the image. An axis error distorts it. A laser ablation with an axis error of just 10° leaves about one third of the original astigmatism. An error of 30° leaves all of it and adds more.

The MS-39 tomographer measures the axis across over 25,000 points — not 4 like a keratometer. But measuring well is not enough: the measurement must be transferred to the laser without error.

Cyclotorsion: the invisible enemy

When the patient lies down, their eyes rotate slightly compared to the seated position in which the measurements were taken. This rotation — cyclotorsion — is typically 2-5° but can reach 10° or more. If the laser does not compensate for it, the astigmatism treatment is shifted from the correct axis.

Regular vs irregular astigmatism

Regular astigmatism — perpendicular and symmetrical meridians — is the most common and simplest to correct. It is treated with an aberration-free profile that reshapes the curvature along a precise axis.

Irregular astigmatism is different: the cornea does not follow a symmetrical pattern. It can result from trauma, previous surgery, keratoconus, or atypical anatomy. It cannot be corrected with standard glasses. It is corrected — when possible — with a corneal wavefront-guided profile, calculated on the specific topography of that cornea. The ForeSight system simulates the result before proceeding.

TransPRK: the advantage for astigmatism

TransPRK SmartSurfACE offers a specific advantage: by not creating a corneal flap, it eliminates the risk of cut-induced astigmatism — a documented problem with LASIK, where the microkeratome or femtolaser can alter curvature during flap creation, especially with high astigmatism.

The absence of a flap-stroma interface makes the ablation surface more homogeneous. The removed profile corresponds exactly to the calculated profile. For technical differences: TransPRK vs LASIK vs SMILE →

SMILE and astigmatism: the documented limitations

The SMILE platform (VisuMax, Zeiss) has two documented structural limitations in astigmatism correction. First: no automatic cyclotorsion compensation. The VisuMax does not have an iris marker recognition system to detect and compensate for ocular rotation in supine position. Centration and axis alignment depend entirely on the surgeon, who must perform manual pre-operative marking at the biomicroscope. Second: treatment centration is entirely operator-dependent, with no active tracking of the astigmatism axis during lenticule creation.

A review published in BMC Ophthalmology showed that anterior corneal astigmatism influences treatment centration in SMILE but not in LASIK, with consequent induction of coma and high-order aberrations. The literature concludes with a general consensus on the superiority of excimer laser-based techniques — LASIK and TransPRK — for the correction of moderate and high astigmatism compared to SMILE.

Astigmatism and presbyopia: simultaneous correction

The PresbyMAX hybrid profile simultaneously corrects astigmatism and presbyopia in the same treatment. The SCHWIND CAM software integrates astigmatism correction into the bi-aspherical multifocal profile. A single treatment for two defects. Learn more: Presbyopia after 45 →

When not to operate

Very mild astigmatism (< 0.50 D) rarely requires surgical correction — the brain compensates. Astigmatism associated with keratoconus, even subclinical, is an absolute contraindication to standard laser. MS-39 topography and the epithelial map distinguish operable regular astigmatism from an irregularity requiring a different approach.