What is it?

What exactly is astigmatism?

Astigmatism (astigmatism) is that refractive error of the eye in which the cornea is elliptical (rather than spherical) with asymmetrical curvatures. The incoming rays of light (optical images) do not focus on one point on the retina, as is normal emmetropic eyes but merge into one line forward or backward (e.g., two orthogonal images) from the retina.

astigmatism1   astigmatism2

Astigmatism usually coexists with myopia or hyperopia. More rarely, the astigmatism may be due to uneven crystalline lens behind the iris of the eye or to disorder of the curvature of the posterior pole (retinal astigmatism).


What causes astigmatism? Main causes:

It is usually due to two different curvature of corneal meridians (axes of the cornea), i.e. of the front part of the eye, which instead of having a spherical shape, it has an oval shape (like an egg). If the focus of the two images lies in front of the retina, we are talking about myopic astigmatism, and if it lies behind, we are talking about hyperopic astigmatism.

astigmatism3   astigmatism4

But it can also be mixed. Astigmatism can be either smooth (when the two axes are perpendicular to each other), or irregular (when the two axes are not perpendicular). Various pathologies (such as keratoconus) may worsen the refractive error.


Astigmatism can be treated with:

astigmatism5   astigmatism6

  • Vision glasses
  • Contact Lenses
  • Refractive surgery (surgery with excimer laser)
  • Surgery to implant a toric intraocular lens (toric intraocular lens) and replacing the crystalline, natural lens of the eye, most of the time, of course, in old ages, in combination with the removal of cataracts