Making a LASIK flap with a mechanical microkeratome is compared to using a femtosecond laser such as the Intralase or Ziemer laser. There are two ways to create a flap in LASIK laser eye surgery. One is to use a mechanical device called a microkeratome. Examples of mechanical (or “bladed”) microkeratomes include the Zyoptix XP, the Hansatome (both by Bausch and Lomb), and the Moria Microkeratome.The other method for creating a LASIK flap is using a femtosecond laser. Examples of femtosecond lasers include the Intralase, the Ziemer,the Victus, the LenSX, the VisuMax (Carl Zeiss), and the Femtec flap making lasers. Both mechanical microkeratomes and femtosecond laser keratomes have undergone significant evolution over the past several years.
The cornea is made of layers similar to the way an onion is. The goal of flap creation is to lift a surface layer of the cornea so that it can be re-positioned back in place after the laser is completed. In other words, the goal is to separate the onion along its layers and not to chop across the onion. The mechanical microkeratome and the femtosecond keratome go about this by different strategies.
The mechanical microkeratome is essentially a very precise spatula that is able to glide between the layers to separate them and allow the flap to be lifted and then re-positioned.
There is much misunderstanding and misinformation about how the femtosecond laser works to create flap. Many people have the mistaken image of the femtosecond laser being like a precise Star Wars light saber that slides through the tissue to create a flap. It turns out the femtosecond laser cannot work this way at all to create flaps. The femtosecond laser is an “ultra short pulse” laser that delivers a burst of energy compacted into an extraordinary small amount of time. This sudden delivery of energy to the tissue transforms the pinpoint spot it hits from tissue into plasma, which is similar to a gas bubble. The expanding gas bubble and associated shock wave create a micro-tear in between the corneal layers. When used to make a LASIK flap, the femtosecond laser delivers hundreds, even thousands, of these ultra short pulses of concentrated energy into the cornea at the desired depth. Each makes a “bubble” — the expanding plasma gas bubble that separates the tissue by force. Because the laser is extremely accurate at achieving a desired depth, each of these cavitation bubbles can be placed at the same depth to create the total surface area of the LASIK flap.
In my next blogs, we will look at some studies that compare the safety of mechanical microkeratomes to femtosecond laser keratomes for LASIK flaps and we will also compare the quality of the surfaces produced by each method.
See Also
Femtosecond Lasers for LASIK Flap Creation: A Report by the American Academy of Ophthalmology
A discussion of using femtosecond laser for creating the flap in LASIK laser eye surgery by the American Academy of Ophthalmology (AAO)
Femtosecond Laser Cleared by FDA
A discussion of the Victus femtosecond laser’s FDA approval.
FDA Approvals Include Femtosecond Lasers
A review of FDA approval of the VisuMax and LenSx femtosecond lasers for both LASIK flap and cataract surgery.
Bladeless LASIK: Creating a LASIK Flap with Precision
All About VIsion discussion of “bladeless” LASIK using the femtosecond laser
Comparative Performance the Zyoptix XP and Hansatome Zero-Compression Microkeratomes
A study comparing two generations of mechanical microkeratomes by Bausch and Lomb for making LASIK flaps.
SBK with the XP Microkeratome
A paper (Shapiro) showing equal precision in making thin SBK LASIK flaps between the Zyoptix XP mechanical microkeratome and the Intralase femtosecond laser.