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Laser Eye Surgery

One of the most common terms used when talking about laser eye surgery is Lasik. However, laser eye surgery and Lasik, are not synonymous. There are two fundamentaly distinct types of laser eye surgery: Lasik and PRK. Lasik is just one type of laser eye surgery.

The term Lasik or LASIK stands for Laser-Assisted-in-Situ Keratomileusis, and represents an effective surgical treatment option for individuals with refractive errors such as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. The Lasik procedure is designed to reduce or correct these refractive errors by permanently changing the shape of the cornea (the clear covering of the front of the eye). The procedure combines the use of microkeratome (a surgical instrument used to perform a flap in the cornea) and the excimer laser to remove thin layers of cornea. When the cornea is reshaped, the eye's focusing power is increased and the individual's visual acuity is enhanced.

The standard Lasik surgical procedure includes five steps:

1). The eye is numbed with anesthetic drops.
2). The surgeon will place a special instrument in the patient's eye in order to hold the eyelids open and prevent blinking.
3). In order to avoid unnecessary eye movements the patient is asked to fixate their eyes on a designated light while the surgeon creates a flap in the cornea with the help of the blade device called microkeratome. The flap stays hinged to the rest of the cornea at one end.
4). A computer-controlled laser light (which was previously programed based on the correction required by the refractive error) is applied to the inner layers of the cornea reshaping it.
5). At the end of the surgery, the surgeon gently replaces the flap to the original position allowing the eye to heal itself naturally.

When Lasik procedure is performed, the cornea surface will be reshaped based on the eye's refractive error that requires correction.

• In patients with hyperopia (farsightedness) (where the cornea is not round, which causes the light to focus behind the normal focal point), the laser beam will steepen the surface of the cornea causing the eye's focus point to be moved closer to the normal focus point for creating a clearer image.

• In patients with myopia (nearsightedness) (where the cornea is too steep causing the images to focus in front of the normal focus point), the laser beam will flatten the surface of the cornea allowing the light to focus at the normal focus point in the back of the eye.

• In patients with astigmatism (where the cornea is curved irregularly impending the light to focus properly on the retina), the cornea is being reshaped in order to allow the eye to focus properly.

There are three advanced alternatives to the standard Lasik procedures: CustomVue Lasik, Conventional IntraLasik, and Custom Vue IntraLasik.

• CustomVue Lasik is a custom-tailored laser vision procedure designed to correct the imperfections of the eye by using the conventional hardware used in a standard Lasik procedure in combination with advance software called Wavefront. This procedure uses a 3-dimensional measurement of the optical system in order to offer an extremely precise, individual vision correction, that cannot be achieved through the traditional Lasik procedure.

• Conventional IntraLasik is an alternative to the standard Lasik, where the corneal flap is created using a computer-guided femtosecond laser beam - significantly decreasing the risks associated with the microkeratome incision.

• Custom Vue IntraLasik is a procedure that utilizes the methods of the above two procedures. The corneal flap is created using the femtosecond laser while the excimer laser that reshapes the cornea is guided based on the CustomVue Watvefront technology. This procedure is the most expensive laser eye surgery.

PRK stands for PhotoRefractive Keratectomy, and is the original laser surgery that preceded Lasik. Although it used to be the most common refractive surgical procedure, PRK became one of the alteratives available for patients that cannot have a flap cut into their cornea and therefore undergo the standard Lasik procedure. PRK is a procedure where the epithelium (outer layer of the cornea) is manually ablated (rather than cutting a flap in the cornea) in order for the laser beam to reshape the remaining corneal tissue. Although PRK requires a longer recovery period and more discomfort following the procedure than the standard Lasik option, PRK reduces the risks associated with having a flap cut in the cornea and the risks of ectasia (a condition in which the inner eye pressure can push against the thinned corneal wall causing it to bulge and worsen the vision).

The PRK procedure includes three steps:

1). The eyes are numbed with a special anesthetic administrated as eye drops.
2). The surgeon will place a retainer in the patient's eye in order to keep the eyelids open and avoid blinking.
3). In order to avoid unnecessary eye movement, the patient is asked to look at a target light, while the laser (programmed by a computer) sends pulses of light which painlessly removes corneal tissue based on the patient's particular prescription.

There are two advanced forms of PRK that are performed: LASEK and Epi-LASEK.

• LASEK, which stands for Laser Assisted Sub-Epithelial Keratomileusis, is a relatively new variation of PRK where a solution of alcohol is used to soften and remove the epithelium (the outer layers of corneal tissue) with the help of a fine blade (trephine). The removed tissue will be placed back after the laser reshapes the underlying corneal tissue. LASEK is an effective alternative to Lasik in patients that have a too thin or too steep cornea. This procedure has been associated with a faster recovery of sensation or nerve function on the cornea.

• Epi-LASEK, which stands for Laser Assisted Sub-Epithelial Keratomileusis, is the newest addition to the refractive eye surgeries. The Epi-LASEK procedure involves a gentle loosening of the epithelium sheet using a blunt, plastic oscillating blade called epithelial separator. The advantage offered by this procedure is that the plastic blade separates the epithelium tissue from the eye, avoiding possible adverse reactions caused by the alcohol solution used in the LASEK procedure. Once the procedure is over, the removed epithelium sheet is placed back on the eye and will be kept in place by a special oxygen-permeable contact lens that will allow the epithelial cells to grow back normally. This procedure is recommended in patients with a thin cornea who don't have enough tissue to cut a flap or in individuals that have professions or hobbies with an increased chances to be hit in the eye (reducing the risk of the flap to be dislocated).

Sources:

American College of Eye Surgeons, American Board of Eye Surgery, What is Lasik?, Date unknown
TLC Laser Eye Centers, What is Laser Vision Correction? Lasik, Date unknown
USA Food and Drug Administration, Lasik Eye Surgery, 2008
Medem, Medical Library, Laser in-situ Keratoermileusis: Lasik, October 1997
AllAboutVision, PRK: The Original Laser Eye Surgery, by Liz Serge, October 2007
AllAboutVision, LASEK Eye Surgery: How it Works by Liz Serge, July 2008
AllAboutVision, Epi-LASEK Eye Surgery: How it Works by Liz Serge, May 2007
WiseGeek, What are the Different Types of Laser Eye Surgery?, Date unknown