LASIK is an operation where the cornea, surface tissue of the eye is reformed to reduce a person’s dependence on glasses or contact lenses. The acronym LASIK means Laser in Situ Keratomileusis because an excimer laser (ultraviolet laser type) is used. It is like other corrective procedures such as photorefractive keratectomy PRK but provides many additional benefits – mainly a faster recovery period as well as a lower chance of developing corneal blurring in high myopias.
Like any other procedure, the results of LASIK surgery are determined based on certain parameters including efficacy, stability, safety, and patient satisfaction. It is important that the ophthalmologist evaluates the patient’s expectations for LASIK surgery and make sure they are realistic.
Basic principles of LASIK
The LASIK procedure initially involves an increase in intraocular pressure of the eye with a suction device. The so-called Femto-Laser (Femto- LASIK) is then used to create a thin flap.
This flap is lifted without being detached from the eye, revealing the layer, the middle part of the cornea, which is sculpted by a computer-controlled Excimer laser beam.
The flap is then repositioned. The cornea holds the flap in place without special intervention. At the end, a therapeutic contact lens is placed for just a few days.
This is a procedure that takes 10 to 15 minutes, so it can be done in one or both eyes during the same session. Eye drops that drop to the surface of the eye are used as an anesthetic and the procedure is done in a state of awakening.
A thorough clinical and paraclinical check of the eye is required through a test that takes place within about an hour. Ideal control requires prior abstinence from contact lenses for 5-7 days.
Refractive errors treated with LASIK.
To achieve clear vision, the cornea and the lens of the eye must properly refract the rays of light so that the images can be clearly focused on the retina. Otherwise, the images are blurry, which may be due to a difference between the curvature of the cornea and the length of the eye. This is also known as a refractive error.
Traditionally, three main types of refractive errors have been described: myopia, hyperopia, and astigmatism. Analysis of human eyes reveals additional abnormalities classified into complex subgroups, often referred to as lower and higher order aberrations.
In myopia the focal point is in front of the retina, so myopic persons are not able to observe objects in long distance. The prevalence of myopia is about 30% in the general population. LASIK corrects myopia by essentially removing tissue in the center of the cornea by flattening it, thus reducing its refractive power.
In hyperopia, the focal point is behind the retina, so these individuals find it difficult to see clearly both nearby and far as well. Although it affects more people than myopia (about 40%), it is less important because of its partial ability to correct it by the adjustment made by the lens of the eye. LASIK corrects hyperopia by removing a ring of tissue around the center of the cornea, thus making it more convex.
Astigmatism is a distortion of the image in the retina due to the abnormal curvature of the cornea. Depending on the axis of the main meridians, astigmatism can be normal or irregular; LASIK can correct astigmatism by removing tissue from the most convex axis of the cornea.