A refractive defect occurs when light fails to focus exactly on the retina due to alterations in the eye shape. That is to say, the patient can not see well because it is out of focus.
THE MAIN REFRACTIVE DEFECTS ARE THE FOLLOWING:
Myopia is a condition in which the length of the eye is too long, causing light rays to focus in front of the retina rather than on it, resulting in blurred distance vision. However Myopes have good nearsightedness.
Hyperopia is a refractive condition in which the light entering the eye is focused behind the retina due to the fact the eye is shorter. Normally they have bad long distance vision and very bad short distance vision.
Astigmatism is a vision condition which occurs when the light focuses on more than one point of the retina. Images appear distorted and blurred. Astigmatism frequently occurs with other vision conditions like myopia (nearsightedness) or hyperopia (farsightedness) but it may also occur by itself. The eye looks like a rugby ball.
Presbyopia is a non-pathological vision condition in which the focus elements of the eye lose their flexibility making it difficult to focus on close objects, for instance when reading. It becomes noticeable in the early to mid-40s. Although it is more emphasized in the farsighted person, in the shortsighted one it is compensated by the previous optical defect (good shortsightedness). Presbyopia can not be modified by refractive surgery.
REFRACTIVE SURGERY – EXCIMER LASER
The Excimer Laser is a technology used for the surgical correction of vision errors ensuring a high degree of precision, control and safety.
This procedure is used to reshape the cornea in order to readjust to the refraction defects.
The laser used is capable of removing tissue molecules without causing heat, thus avoiding structural damage to the cornea.
This surgery reduces the defect between 90% and 100%. Anyway, these small refractive defects can be solved by using rest glasses.
LASIK TECHNIQUE (Laser-Assisted In Situ Keratomileusis):
This technique offers several benefits when compared to other forms for the correction of vision, due to the fact that it is performed under the protection of a "lid" or "flap" of tissue. As a result of this, there is a smaller amount of surface tissue for cicatrisation.
WHO CAN BE OPERATED WITH THIS TECHNIQUE?
In general, the ideal patient for Lasik should be over age 25 and his corneas should be undamaged. The pre-operative evaluation procedures for patients considering surgery include: a Topography (map of the cornea's surface) and a Pachymetry (corneal thickness measurement). Furthermore, patients should not have experienced significant increases in their prescriptions during the last twelve months.
1. Your eyes are first anesthetized with special drops over the cornea. A kind of retainer is placed over your eye to keep your eyelids open. The surgeon will use an instrument called microkeratome to lift a thin flap on the cornea. During this procedure the patient is likely to experience a little pressure and see all black during a few seconds.
2. During the procedure, and in very few seconds, an ultra-violet light and high power Laser Excimer pulses reshape the cornea. Adjusting the laser light pulses it is possible to treat moderate and low levels of myopia, astigmatism and hyperopia.
3. Once the tissue has been corrected the corneal flap is replaced to its original position. Due to the cornea’s extraordinary natural quality of adherence, no suture is necessary.
The complete procedure takes no more than 10 minutes and it is not painful. Some patients report post-operative gritty feeling in the eye, tearing and sensitivity to light which can be normally relieved by means of analgesic medication.
Vision improves immediately after the operation. Most patients return to their ordinary activities in one or two days.