Index
THEastigmatism it's a defect (o error) refractive caused by aimperfection in the geometry of the cornea or, more rarely, del crystalline. Most commonly it is loss of spherical symmetry in the cornea to determine astigmatism, sometimes, however, this visual defect is caused by irregularities in the surface of the lens.
Symptoms
In the presence of astigmatism, the images of the outside world cannot be correctly focused on the retinal plane, each point of the image is projected in two or three different points of the retina and the images of the objects observed are blurred at any distance.
Diagnosis
Astigmatism can be highlighted using a eye examination, both with the simple reading of the characters of the optotypical table and with an in-depth instrumental investigation.
The most used instrumental tests are:
• theautorefractory, which provides corneal and refraction parameters,
• the corneal topography, which allows you to quantify the extent of astigmatism with the relative axis and a mapping of the corneal curvature at each point,
• it IOL-Master, which measures the length of the eyeball and corneal curvature,
• the pachymetry, which calculates the corneal thickness and allows, in the presence of high astigmatism, to exclude the presence of pathologies such as keratoconus,
• analysis with PENTACAM, which allows a "stratigraphic" analysis of the entire corneal structure to be carried out, highlighting any alterations present in the various corneal layers.
How does an astigmatist see?
Correction
Astigmatism can be corrected with the use of glasses with cylindrical or toric lenses, which can also have a negative or positive dioptric power in case of simultaneous presence of myopia or hyperopia. As an alternative to glasses, glasses can be used toric contact lenses.
Refractive surgery
Astigmatism can be permanently corrected thanks to the refractive surgery. There are various refractive surgery techniques, all based on modifying the curvature of the cornea, in order to compensate for the refractive defect.
La photorefractive keratectomy (PRK, Photo Refractive Keratectomy) is a refractive surgery technique that has been performed for several decades to correct the refractive defect and eliminate glasses or contact lenses thanks to the use of a excimer lasers.
PRK surgery is performed under local anesthesia and lasts for a few minutes. The excimer laser allows to achieve a "vaporization" of the most superficial corneal structure, which includes the corneal epithelium, Bowman's membrane and part of the corneal stroma. Thanks to this procedure, the images are refocused on the retinal plane and the patient can see correctly again in a clear manner in a short time, without the need for glasses or contact lenses.
The technique iLASIK (Intra-Laser In Situ Keratomileusis) was developed after PRK and differs from the latter in the method of application of the excimer laser: in PRK the laser is applied to the superficial part of the cornea after removing the outermost epithelial layer, while in iLasik the laser is applied to the innermost stromal layer of the cornea thanks to the creation of a "corneal flap”, which consists of a thin layer of cornea that is made by making an incomplete circular incision with a femtosecond laser and overturning the very thin layer of cornea included inside the incision and covering the stroma.
The possibility of modeling the cornea by acting directly on the stroma allows for a immediate visual recovery e absence of pain in the postoperative period.
Both PRK and iLasik are characterized by a extremely high level of security, unrivaled in the field of eye surgery, and allow to achieve in properly selected patients results close to 100% with respect to the objectives set.
iLasik represents an evolution over PRK and has some advantages over the latter, however not all patients are suitable for this procedure. The choice of the type of refractive surgery to adopt for each specific candidate, iLasik or PRK, must be evaluated by the ophthalmologist on the basis of certain anatomical parameters of the eye.
Pathology and treatment on video
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