A microkeratome is a specialized surgical instrument used primarily in refractive eye surgery procedures such as LASIK (laser-assisted in situ keratomileusis) to create a thin corneal flap. The instrument has a diamond or stainless steel blade that cuts a uniform, hinged flap in the cornea, allowing access to the underlying corneal stroma. This flap is then folded back during surgery to expose the stromal bed for ablation and reshaping with an excimer laser. At the end of the procedure, the flap is delicately placed back in its original position, where it naturally reattaches on its own.
Types of Microkeratomes
There are generally two types of instrument heads used in LASIK: mechanical and femtosecond laser-assisted.
Mechanical Microkeratomes
Mechanical instruments employ a movable blade that glides across the cornea with microscopic cuts. The head comes in varying cutting depths and diameters depending on the corneal thickness and flap size needed for the LASIK procedure. Mechanical instruments are often preferred by experienced surgeons as they provide a more controlled cut. However, they do carry a slightly higher risk of uneven or irregular flap creation.
Femtosecond Laser Microkeratomes
Femtosecond laser Microkeratome utilize an infrared femtosecond laser beam to precisely cut corneal tissue without physically contacting the eye. This allows creation of ultra-thin, customized flaps with sharper, more predictable edges compared to mechanical instruments. Safety and accuracy are improved as well by eliminating blade contact. However, femtosecond lasers are more expensive than mechanical alternatives. They are now becoming the gold standard for LASIK as the technology continues advancing.
Workings
Regardless of the type used, here is a basic overview of how a instrument works during LASIK surgery:
1. After administering anesthesia and creating a lid speculum to keep the eyes open, vacuum suction ring is applied to the cornea to stabilize it.
2. Microkeratome head is positioned at the corneal vertex and engaged via a hinged arm actuator.
3. For mechanical instruments, the micro-thin blade oscillates back and forth in a sweeping motion as it traverses across the cornea. For femtosecond lasers, an infrared beam precisely cuts a flap pattern.
4. This slicing action creates a very thin, partial-thickness corneal flap of consistent thickness and diameter.
5. The hinged flap is then gently lifted away with a microsurgical instrument to fully expose the underlying corneal stroma.
6. Excimer laser photorefractive keratectomy (PRK) is then performed to reshape the stroma as needed to correct vision.
7. At completion, the re-flap is carefully replaced over the stromal bed, where natural wound healing seals it back in perfect alignment.
Impact of Microkeratome Design on Outcomes
While all instruments aim to create a safely hinged corneal flap, design factors do impact outcomes:
Blade Material - Stainless steel blades minimize swelling but can cause irregular cuts. Diamond or polymer-coated blades cut more smoothly with less inflammation.
Blade Configuration - Oscillating blades sweep in an arc for smooth cuts vs. continuously rotating blades with higher risk of irregularities.
Blade Angle - Blades angled at 60-90 degrees from vertical produce predictable flaps vs. angled blades that can cause asymmetry.
Cutting Depth - Adjustable heads allow customized flaps of 90-160 microns for thinner cuts without perforation risk.
Overall, continuously evolving instrument designs combined with technological advances like femtosecond lasers have rendered LASIK safer and more effective than ever before. Precision corneal flap creation remains the key first step enabling the remainder of this highly successful refractive surgery.
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