The clear vision of objects depends on adequate power optical system of the eye. The cornea and lens of the two lenses constituting the optical system of the eye responsible for focusing the image on the retina. Specialists in Ophthalmology , say that when the power of this system is adequate, the image is focused exactly on the retina, and a clear picture is obtained.
Nearsightedness, farsightedness and astigmatism
When the power of the optical system of cornea and lens is greater than normal, the image is focused in front of the retina, and blurry vision is obtained. It is the defect called myopia. The opposite problem, namely, a less powerful than normal optical system, and therefore an image formation behind the retina, hyperopia occurs.
At other times, the problem is that the cornea is not perfectly spherical surface, such as a football, presenting different curvatures on its front surface which makes it more resembles a rugby ball. In these cases a distorted image of objects is also obtained: the problem called astigmatism. Most often, this defect is associated with one of the above, ie, most of myopic or hyperopic eyes also have some degree of astigmatism.
All these problems can effectively refractive corrected with an appropriate prescription, both glasses and contact lenses. But today it is also possible to correct by refractive surgery.
Laser refractive surgery
Refractive surgery includes various surgical techniques developed to reduce dependence on glasses or contact lenses. The purpose of all these techniques is to introduce a number of changes in the eyeball in order to improve the targeting of the image on the retina without correction, not to improve their visual acuity.
With few exceptions, refractive surgery is not medically indicated, so that the decision to perform the procedure rests with the patient. The physician's role is reduced to providing objective and truthful information about potential risks and benefits for the patient can decide freely, and to indicate the most suitable technique for each case, since each has its indications depending on the degree of myopia or astigmatism the patient.
To access any of these techniques is a prerequisite to be older than 21, and that the refractive error is relatively stable, unchanged in the last one year.
Technique of laser refractive surgery
The excimer laser is a technique for modifying the anterior surface of the cornea by the action of an invisible high-energy light. To eliminate some of the more superficial layers of the cornea with such light, managing to reduce the anterior curvature of the cornea. The end result is a flatter cornea and therefore less optical power. Light rays now form a closer focus on the retina, thereby reducing or eliminating the need for glasses or contact lenses for useful vision.
Excimer Laser is indicated for:
- Low to moderate myopia, ie, less than 7 diopters
- Astigmatism up to 4 diopters
- The lower hyperopia at 4 diopters
The surgical procedure used is called LASIK. In it, a horizontal cut on the cornea is done by a special laser called femtosecond. With this laser incomplete resection of a corneal lenticule, so that said lenticule can be everted like the covers of a book were, the bonding zone acting as a hinge is made. On the remaining corneal tissue removal (photoablation) with other excimer laser is performed to correct the desired number of diopters, after which the lenticule placed back in its original place, where it is firmly attached after carefully drying their edges, without any suture.
The intervention, which lasts about 10 minutes, is performed on an outpatient basis and with drops of topical anesthetic. After the operation there may be some blurring and foreign body sensation vision, which must not normally exceed 24-48 hours.
Generally, in 24-48 hours useful vision that allows a normal life recovers. However, the maximum vision that can be achieved can take between 1 and 3 months to achieve, depending on the magnitude of the initial defect. Usually the distant vision is recovered before the close.
Risks of laser refractive surgery
Possible complications that can occur are: abnormal corneal lenticule cut, corneal infection, corneal inflammation, and hyper or undercorrection unwanted. The most serious, although rare, is corneal infection. These complications are rare.
Sometimes it may happen that, in low-light situations, to dilate the pupil size of the optical zone carved by Laser is exceeded. This can cause the patient to experience glare or halos around lights, more intense during the immediate postoperative period, which usually improve over time.