11 April 2011

Why Does Corneal Thickness Affect Lasik Eye Surgery?

One of the key in the preoperative evaluation of surgery Lasik is corneal thickness of the patient. The cornea is the clear dome which forms the front of the eye. It functions as a lens and represents approximately 60% of the power of focusing your eyes. LASIK surgery works with a laser to reshape the cornea and alter its focusing power.LASIK uses a very particular type of laser called an excimer laser. This product specific wavelength light laser has very unique properties when it contacts human tissue. Essentially, it causes tissue to spray in a Manor House very precise with very little thermal effect. In other words, it can very accurately remove tissue without causing any combustion, therefore there is no collateral damage tissue. By using an optical system, controlled, this laser light can be directly on the surface of the cornea it remodel with incredible precision.LASIK requires some amount of corneal tissue to be removed to change its form. Over the years, surgeons have developed the generally accepted principles as margins of reliable security for what tissue can be removed and how many should stay. It is believed generally that if too tissue is removed from the cornea's structural integrity can be compromised and it will be weakened. Any weakness of the cornea can lead to distortions of its form which are unpredictable and irregular. The weakness may also be progressive causing something called ectasia where part of the cornea grows outward.Cornea thickness of each is different, and it is an essential part of the of Lasik preoperative assessment of the measure. The most common way to measure the thickness of the cornea is ultrasonic, but there are also a number of new optical instruments which can take similar measures. An average thickness of the cornea is usually in the neighbourhood of 550 microns, but there is a relatively large variation with some being more thick and some diluent. In some cases, an exceptionally thin cornea may be a sign of weakness or something called the Keratoconus. These people should be eliminated before having Lasik because their corneas are already inherently weak. This diagnosis is made by measurements of the thickness of the cornea, shape of the cornea or topography and other clinical signs which can often be seen by an ophthalmologist formed under the microscope. Anybody determined by their eye surgeon to have the Keratoconus should be excluded from having Lasik Surgery based on this information only.When executing Lasik, the surgeon can remove tissue to a certain depth. Most surgeons will want to leave a base of at least 250-300 microns in intact corneal security. LASIK requires a certain amount of fabric used to create a surface flap is lifted before road excimer laser removes tissue and redefines the cornea optically. The thickness of the Lasik flap is essential because the thinner the Rabat, the treatment of Lasik more can be done before reaching the intact core minimum of 250 to 300 microns. Once again, the feeling is that if the depth of processing considerably exceeds this point, that the structural integrity of the cornea can be compromised.With the older technology, a bladed instrument called a microkeratome is used to create the Lasik flap. A typical thickness flap using this instrumentation would be approximately 160 microns. So for a patient with a 550 micron cornea, after the creation of the Rabat, the remaining fabric would 550-160 or 390 microns in thickness. If the surgeon wants to leave an intact basis of 300 microns, leaving 90 microns of tissue to be removed and reshaped for the optical effect. Generally, for each diopter of myopia, it requires the removal of about 12 - 15 microns of tissue. This treatment is only possible for up to-6 to-8 Diopters in this patient.New technology of Lasik is completely free of blade and uses another laser (a femtosecond laser) to create the flap instead of a microkeratome blade. These femtosecond lasers can make Lasik flaps which are much thinner, approximately 100 microns in thickness over 160 microns with precision. This additional 60 microns leaves more than fabrics for optical treatment for 5 or 6 diopters of further possible processing in an average person. That is why when you use the femtosecond laser systems, higher Lasik treatments can often be performed even in patients with a little more thin corneas. It is the measure of the thickness of the cornea important as i