ASTIGMATISM

PATHOLOGY

The astigmatism is a refractive defect, caused by an alteration of the curvature of the cornea, which is no longer similar to that of a football, but is rather similar to that of a rugby ball and, therefore, is not the same on the different meridians. From this the incapacity of the eye derives to focus on the image of an object or a person.

Before reaching the retina, the luminous rays coming from the external world must cross the cornea and the lens and it is, therefore, necessary that these natural lenses possess a correct focusing power. In particular, the total astigmatism of the ocular diopter is the result of the various combinations of astigmatisms of the cornea and of the lens.

Astigmatism can have origin, in fact, both from the cornea and from the lens: Therefore, visual alterations will occur both if the cornea presents an irregular sphericity and if the surface of the lens is not perfectly spherical or its optic axis does not correspond to the visual axis.

SYMPTOMS

The symptoms often reported by the patient are a blurry vision or in more serious cases also  double or distorted distant or near visions.

DIAGNOSIS

It is possible to make an astigmatism diagnosis during an eye examination by an ophthalmologist, both with the simple reading of the characters of the eye chart and wit an in-depth instrumental examination.

The instrumental tests that have a more widespread use are:

– the Detective system for ocular refractive error measurement Autorefrattometria which provides corneal and refraction parameters

– the Topography which enables to quantify the extent of astigmatism with the relevant axis and a map of the cornea curvature in each point

– the IOL Master which measures the length of the eyeball and the cornea curvature

– the Pachymetry which calculates the thickness of the cornea and makes it possible, in the presence of high astigmatism, to exclude the presence of pathologies such as the  keratoconus

– the analysis with PENTACAM or other advanced technologies which enable to carry out a “stratigraphic” analysis  of the entire corneal structure evidencing any alterations existing in the several corneal layers.

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TREATMENT

CORRECTION

Astigmatism can be corrected by the use of glasses with cylindrical or toric lenses, which can have a negative or positive dioptric power in case of the simultaneous presence of shortsightedness and hypemethropy or, in alternative, rigid or toric contact lenses can be used.  

SURGICAL THERAPY 

If the astigmatism is of corneal origin, then it is possible today to use the refractive surgery and permanently correct the curvature of the cornea, in such a way as to restore its spherical symmetry and compensate in this way the refractive defect avoiding the use of glasses or contact lenses.

Among the surgical methods more frequently used we point out: PRK, i-LASIK and SMILE.

The refractive surgery is executed under local anesthesia, without pain both during and after surgery, it lasts only a few minutes and consists in modifying the curvature of the corneal surface.  The “excimer laser” enables to have a disintegration or “vaporization” of the more superficial corneal structure, i.e. the corneal epithelium, the Bowman membrane and a part of the stroma. Thanks to this surgery, the eye can focus again the images on the retinal plan and, in particular in the macular area and the patient can see again distinctly in a very short time without the need of glasses or contact lenses.

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