During the initial years of this procedure, the flap was created by a mechanical microkeratome but this was superseded by sophisticated Femtosecond laser technology. There were a number of Femtosecond lasers built that were capable of creating a flap as described, more reliably and accurately than the microkeratome. The drawback with procedures requiring a flap, no matter the method of creation, is the fact the strong outer ‘eggshell' of the cornea is cut through 340-degrees, marginally weakening the cornea. The flap area never heals completely, so full strength never returns, and the flap can be displaced, even years later. Additionally, the extent of the surface 340-degree entry through the outer ‘eggshell’ cuts through many of the corneal nerves, producing the propensity for dry eye symptoms which is quite common after LASIK. This procedure has nevertheless produced excellent visual results over the last few decades. Enter the third generation laser procedure – the Femtosecond. Laser engineers at Zeiss quickly realised that with Femtosecond laser technology, separation did not have to be restricted to the single nature of a flap interface separation, but if measured accurately enough, a second pass below the first of a flap could generate enough separation to allow the tissue in between - called a lenticule - to be removed and create the necessary shape change to correct vision. The extensive 340-degree cut is no longer necessary as the small amount of tissue that makes up the lenticule can be separated, folded and removed from a small incision only the size of the old hinge in the LASIK technique (approximately three millimetres). This has represented a huge paradigm shift in the concept of Refractive Laser Correction, as we can now remove the appropriate amount of tissue from the inert centre of the cornea without disturbing the strong outer ‘eggshell’. This means less corneal nerves are cut, less dry eyes, and less susceptibility to trauma while maintaining outstanding visual results. It is also an advantage that only one type of laser is required for this procedure unlike the two which are required for LASIK. The extensive 340 degree cut is no longer necessary 14 Pindara Magazine 2016
Pindara Private Hospital Magazine - Issue Eight
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