Technical Info About the Femtosecond Laser
The femtosecond laser is an infrared laser that can treat tissue very precisely with significantly less heat created than other laser treatments - a big advantage in laser eye surgery. Femtosecond lasers work with ultra-short light impulses that need only a billionth of a second to create a spot as tiny as 1/100mm. To illustrate the extremely short pulse time: In one second, light travels 7.5 times around the earth, however, in one femtosecond, it only travels one half of the thickness of a hair!
The Preparation of the Corneal Lamella with the Femtosecond Laser–in Detail:
Contrary to traditional lasers, the energy of the laser beam from a femtosecond laser does not affect the tissue on the corneal surface, but reaches a specific predetermined depth inside the cornea. Very high energy levels can thereby be achieved through intense focusing of the laser beam. The point of focus of the laser beam allows material to be divided at the molecular level (photo-disruption), gently separating the tissue. The surrounding corneal tissue remains undisturbed without damage. The femtosecond laser scans the cornea starting at one edge and works its way towards the other side (Ill. 3a). The laser beam produces a layer of tiny bubbles in exactly the desired location depth of the cornea. This enables the corneal flap to be opened and lifted to the side like in traditional LASIK. The final treatment with the excimer laser is then identical to traditional LASIK.
The Laser energy is focused at a precisely predetermined depth of the corneal tissue.
A micro bubble consisting of gas and water is generated (diameter: 5 - 12 μm). The bubble expands and separates the surrounding corneal layers.
The photo-disruption results in a mixture of carbon dioxide (CO2) and water. The epithelial pumping action makes sure the latter is absorbed. What remains, is the separated corneal tissue.
In summary, thousands of laser impulses separate the corneal lamella in the entire flap area. Thus, the Femtosecond laser has made an incision without ever touching the cornea, and because of this is also called a laser keratome. Subsequently, the flap can easily be flipped over by a blunt spatula.