What Is A Microkeratome And Why Is It Used In Laser Eye Surgery?

If you have looked into having Laser eye surgery (Lasik) you have probably heard of an instrument called a microkeratome

. Have you wondered what exactly the microkeratome is and what role it plays in Lasik? These are excellent questions and many people never fully comprehend the answers.

To understand completely, it is helpful to look back at the early genesis of Laser eye surgery. In the beginning, these surgeries were called PRK (photorefractive keratectomy) and they did not involve a microkeratome. An excimer laser was used to directly treat and reshape the outer surface of the cornea in order to change the optics of the eye.

Optically PRK is quite effective but there is a major drawback. When PRK is performed, there is a large bare treated area on the front of the cornea which is like a giant scratch on your eye. If you have ever had a scratch on your cornea, you know that it can be excruciatingly painful and can take some time to heal.

In the case of PRK, it usually takes about 3 days for the outer surface epithelium of the cornea to close and it takes some time thereafter for the swelling and healing to stabilize. Typically, a bandage contact lens is placed on the eye for 3 days to protect it and to increase comfort.

Lasik was developed by combining PRK with an older technology, the microkeratome, from another kind of eye surgery called ALK. The purpose of combining these techniques was to reduce the recovery time and increase comfort compared to PRK.

The microkeratome is able to cut a thin layer of tissue off of the surface of the cornea. This layer can be hinged and carefully lifted and folded back out of the way. Imagine it like a wall calendar where the previous month can be folded back to expose the next page underneath. Once this flap of tissue is out of the way, the excimer laser can optically treat and reshape the underlying cornea. Once finished, the flap can be replaced to cover the treated cornea.

The flap takes the place of the bandage contact lens of PRK and acts as a natural tissue bandage, if you will. It allows the surface of the cornea to remain practically intact with no large scratch on the surface. Vision returns quickly and often patients can see 20/20 by the next day. Pain is also usually minimal and limited to the early hours after the procedure. This flap is delicate at first and patients are advised not to rub their eyes in the early days following Lasik, but over time it heals and seals down so that patients have no functional limitations.

The early microkeratomes actually used physical razor blades and high speed oscillating mechanisms to work. In the last few years, they have evolved so that no blades or moving gears are needed. A special laser called the femtosecond laser can create a flap with far greater precision and accuracy than the older instruments.

These laser microkeratomes also have a much lower incidence of flap related problems like free cut flaps, button-holes in the flaps, or metal fragments/oils dragged beneath the flaps. Because of their design, the surgeon also has much better control because he can actually see the flap being created and even adjust its size and shape on a computer screen as needed to customize it for the eye of any individual.

In summary, the use of the microkeratome in Laser eye surgery has greatly influenced the procedure allowing greater patient comfort and faster recovery compared to PRK. The evolution of the femtosecond laser microkeratome has taken the procedure light years ahead with greater safety and an incredible level of precise control that allows us the flexibility to customize Lasik flaps in ways that were inconceivable before.

by: John Suson

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