Written on Jun 22, 2010 at 10:06 PM by LASIK Guider
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You know that each LASIK procedure involves making a flap in the cornea.



But do you know...



What is LASIK flap, exactly? Why LASIK flap is required? How LASIK flap is created? What are the recent advances in LASIK flap creation? What are the characters of the ideal LASIK flap? How does the LASIK flap heal? And what are the LASIK flap complications?



Those are some of the most frequently asked questions about LASIK flap, and today I will answer them to give you a clear grasp on LASIK surgery.




What is LASIK flap?

LASIK Corneal Flap & Hinge

LASIK flap is a circular strip of the outer corneal tissue dissected away from the underlying corneal layers but left attached in one segment called the hinge. The most common location for the hinge is either the nasal (on the side) or the superior (upper) position.




Nasal hinge vs. upper hinge LASIK flaps: Which is better?

In the classic LASIK technique, the hinge position was typically nasal. Nowadays most LASIK surgeons create LASIK flaps with upper hinges. The flap can then be lifted up from the bottom, hence the name: down-up LASIK.



The down-up LASIK technique is more physiologic because the blinking helps keep the flap in position and contributes to its smoothing. Also the gravity tends to position the flap in the best way to promote healing.



On the other hand, LASIK surgeons who prefer the classic nasal hinge flap point out that creation of a nasal hinge flap reduce the risk of post-LASIK dry eye. In addition, it is easy to cut a nasal flap with many microkeratomes since there is no eyebrow to obstruct the path of the instrument.




Why LASIK flap is required?

LASIK is a type of laser vision correction surgery called “lamellar refractive surgery” because it is performed between the layers of the cornea. The LASIK flap is necessary in order to expose the deeper corneal layers to the excimer laser energy that reshapes your cornea to improve your vision.




How LASIK flap is created?

In conventional LASIK, your surgeon will use a hand-held device known as a microkeratome to create the LASIK flap. But if you are undergoing all-laser LASIK, your surgeon will make the LASIK flap using a type of high energy laser (femtosecond laser or IntraLase) instead of a blade.




Is IntraLase better than microkeratome for  flap creation?

LASIK safety and results are excellent using the microkeratome when performed by an experienced LASIK surgeon for well selected patients. However, the introduction of the IntraLase laser allowed for greater precision and predictability when creating the LASIK flap.




What are the characters of the ideal LASIK flap?

  • Smooth and uniform surfaces
  • Uniform cut depth
  • Regular and suitable diameter for the refractive ablation
  • A hinge that is sufficiently large as well as displaced from the laser ablation

What is the difference between IntraLase LASIK flap and conventional LASIK flap?

The microkeratome flap is variable in its dimensions, since its creation is influenced by many anatomical factors such as steepness and thickness of each individual cornea. Conversely, the IntraLase laser flap maker can create a LASIK flap with the precise dimensions specified by the surgeon.



Bladeless LASIK Flap vs. Conventional LAISK Flap

IntraLase Flap

Microkeratome Flap

IntraLase LASIK Flap

MicroKeratome Flap

Precise flap diameter

Irregular flap shape & diameter

Uniform thickness

Non-uniform thickness

Optimal hinge location

Varying hinge location

Beveled edge

Uneven edge

Precise centration

Decentered




What is the ideal LASIK flap thickness?

Traditional LASIK flaps were generally ranged in thickness from 140 to 180 microns. This is about one third of the total corneal thickness, given that the average normal cornea is about 540 microns in thickness.



Nowadays, with the newer types of microkeratomes and IntraLase lasers that can create thinner flaps, many LASIK surgeons prefer a flap thickness between 100 and 130 microns. The reason for this shift toward thinner LASIK flaps is

  • To maintain the corneal stability and avoid serious LASIK complications such as corneal ectasia by maximizing the amount of posterior corneal tissue that left untouched (This amount should be at least 250 microns and preferably 300 microns) after the LASIK procedure.
  • To allow correction of higher degrees of refractive errors since thinner LASIK flaps preserve a greater amount of corneal tissue under the flap for treatment.
  • To allow greater ability to perform enhancements, if required in the future.
  • To reduce the LASIK recovery period since thinner flaps heal faster.
  • To reduce the risk of post-LASIK dry eye syndrome since thinner flaps cause less damage to the corneal nerves.

What is the appropriate LASIK flap diameter?

Usually the diameter of the LASIK flap is more than 8.0 mm in nearsightedness and more than 8.75 mm in farsightedness. Larger LASIK flaps are better and required when the treatment zone is large; for example, in hyperopic LASIK, mixed astigmatism or custom wavefront LASIK. A larger flap is also useful if LASIK retreatment is expected.




How does the LASIK flap adhere to the underlying cornea?

After completion of the laser treatment, your surgeon will replace the flap into its original position and the LASIK procedure is complete. No stitches are required as the flap stays in place and adheres to the underlying corneal tissue by the following natural mechanisms:

  1. Surface tension
  2. Stickiness of molecules in the corneal stroma by  a gluey  substance secreted by the corneal cells (glycosaminoglycans)
  3. Suction pressure by corneal endothelial pump
  4. Mechanical approximation of tissues

How long does it take for the flap to heal after LASIK?

The LASIK flap Healing process starts immediately once the flap is replaced by the LASIK surgeon after the laser treatment. However, the healing process time will vary from person to person due to individual healing differences.



Generally, the flap will be secure within 2 weeks and after one month you can return to all activities, including sports. However, if there is any risk that you might take a direct blow to the eye, you should wear protective eyewear (e.g., protective goggles).




What are the LASIK flap complications?

Many complications unique to LASIK are related to the creation of the corneal flap. Those complications include free flaps, thin flaps, incomplete flaps, flap buttonholes, flap decentration and epithelial defects.



However, with the improvement in microkeratome technology and the introduction of IntraLase laser, the incidence of LASIK complications has dropped markedly.

2 comments:

Amar August 2, 2013 at 7:33 AM  

If LASIK flap is irregular after LASIK is it ok to perform PRK? and how far it will help in improvement of vision?

LASIK Guider August 5, 2013 at 12:13 AM  

There are several types of flap complications including thin flaps, thick flaps, irregular flaps, partial or incomplete flaps, buttonholed or donut-shaped flaps, free caps (the flap is cut completely off), flap striae (wrinkles), and decentered flaps.
Irregular LASIK flap is one of LASIK flap complications that may result from eye movement or malfunction of the microkeratome (the device that cuts the flap). Surface ablations such as PRK which do not require cutting a corneal flap are an option to improve vision after flap complications.
How far your vision will improved will depend on your case, your doctor should discuss the best option for you after examination of your eyes and assessment of your investigations.

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