LASIK - Procedure

There are several necessary preparations in the preoperative period. The operation itself involves creating a thin flap on the eye, folding it to enable remodeling of the tissue beneath with a laser. The flap is repositioned and the eye is left to heal in the postoperative period.

Preoperative
Patients wearing soft contact lenses are usually instructed to stop wearing them 5 to 21 days before surgery. One industry body recommends that patients wearing hard contact lenses should stop wearing them for a minimum of six weeks plus another six weeks for every three years the hard contacts have been worn. Before the surgery, the patient's corneas are examined with a pachymeter to determine their thickness, and with a topographer to measure their surface contour. Using low-power lasers, a topographer creates a topographic map of the cornea. This process also detects astigmatism and other irregularities in the shape of the cornea. Using this information, the surgeon calculates the amount and the locations of corneal tissue to be removed during the operation. The patient typically is prescribed and self-administers an antibiotic beforehand to minimize the risk of infection after the procedure.

Operation
The operation is performed with the patient awake and mobile; however, the patient is sometimes given a mild sedative (such as Valium) and anesthetic eye drops.
LASIK is performed in three steps. The first step is to create a flap of corneal tissue. The second step is remodeling of the cornea underneath the flap with the laser. Finally, the flap is repositioned.

Flap creation
A corneal suction ring is applied to the eye, holding the eye in place. This step in the procedure can sometimes cause small blood vessels to burst, resulting in bleeding or subconjunctival hemorrhage into the white (sclera) of the eye, a harmless side effect that resolves within several weeks. Increased suction typically causes a transient dimming of vision in the treated eye. Once the eye is immobilized, the flap is created. This process is achieved with a mechanical microkeratome using a metal blade, or a femtosecond laser microkeratome (procedure known as IntraLASIK) that creates a series of tiny closely arranged bubbles within the cornea. A hinge is left at one end of this flap. The flap is folded back, revealing the stroma, the middle section of the cornea. The process of lifting and folding back the flap can sometimes be uncomfortable.

Laser remodeling
The second step of the procedure is to use an Excimer laser (193 nm) to remodel the corneal stroma. The laser vaporizes tissue in a finely controlled manner without damaging the adjacent stroma. No burning with heat or actual cutting is required to ablate the tissue. The layers of tissue removed are tens of micrometres thick. Performing the laser ablation in the deeper corneal stroma typically provides for more rapid visual recovery and less pain than the earlier technique, photorefractive keratectomy (PRK).
During the second step, the patient's vision will become very blurry once the flap is lifted. They will be able to see only white light surrounding the orange light of the laser, which can lead to mild disorientation.

Currently, manufactured Excimer lasers use an eye tracking system that follows the patient's eye position up to 4,000 times per second, redirecting laser pulses for precise placement within the treatment zone. Typical pulses are around 1 millijoule (mJ) of pulse energy in 10 to 20 nanoseconds.

Repositioning of flap
After the laser has reshaped the stromal layer, the LASIK flap is carefully repositioned over the treatment area by the surgeon and checked for the presence of air bubbles, debris, and proper fit on the eye. The flap remains in position by natural adhesion until healing is completed.

Postoperative care
Patients are usually given a course of antibiotic and anti-inflammatory eye drops. These are continued in the weeks following surgery.

Patients are usually told to sleep much more and are also given a darkened pair of shields to protect their eyes from bright lights and protective goggles to prevent rubbing of the eyes when asleep and to reduce dry eyes. They also are required to moisturize the eyes with preservative-free tears and follow directions for prescription drops. Patients should be adequately informed by their surgeons of the importance of proper post-operative care to minimize the risk of complications.

Photorefractive Keratectomy - Definition

Photorefractive keratectomy (PRK) and Laser-Assisted Sub-Epithelial Keratectomy (or Laser Epithelial Keratomileusis) (LASEK) are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lenses.

The first LASEK procedure was performed at Massachusetts Eye and Ear Infirmary in 1996 by ophthalmologist, refractive surgeon, Dimitri Azar.

The procedure was later popularized by Camellin, who coined the term LASEK for laser epithelial keratomileusis.

LASEK and PRK permanently change the shape of the anterior central cornea using an excimer laser to ablate (remove by vaporization) a small amount of tissue from the corneal stroma at the front of the eye, just under the corneal epithelium. The outer layer of the cornea is removed prior to the ablation. A computer system tracks the patient's eye position 60 to 4,000 times per second, depending on the brand of laser used, redirecting laser pulses for precise placement. Most modern lasers will automatically center on the patient's visual axis and will pause if the eye moves out of range and then resume ablating at that point after the patient's eye is re-centered.

Radial Keratotomy - Definition

Radial keratotomy (RK) is a refractive surgical procedure to correct myopia.

LASIK - Technology

The LASIK technique was made possible by the Colombia-based Spanish ophthalmologist Jose Barraquer, who, around 1950 in his clinic in Bogotá, Colombia, developed the first microkeratome, and developed the technique used to cut thin flaps in the cornea and alter its shape, in a procedure he called keratomileusis.

Stephan Schaller assisted in this landmark procedure. Barraquer also researched the question of how much of the cornea had to be left unaltered to provide stable long-term results.

Later technical and procedural developments included RK (radial keratotomy), developed in Russia in the 1970s by Svyatoslav Fyodorov, and PRK (photorefractive keratectomy), developed in 1983 at Columbia University by Dr. Steven Trokel, who in addition published an article in the American Journal of Ophthalmology in 1983 outlining the potential benefits of using the Excimer laser in refractive surgeries. (RK is a procedure in which radial corneal cuts are made, typically using a micrometer diamond knife, and is completely different from LASIK).

In 1968 at the Northrup Corporation Research and Technology Center of the University of California, Mani Lal Bhaumik and a group of scientists were working on the development of a carbon-dioxide laser. Their work evolved into what would become the Excimer laser. This type of laser would become the cornerstone for refractive eye surgery. Dr. Bhaumik announced his team's breakthrough in May 1973 at a meeting of the Denver Optical Society of America in Denver, Colorado. He would later patent his discovery.

The general term for changing a patient's optical measurements by means of an operation is Refractive Surgery. The introduction of lasers in refractive surgeries stemmed from Rangaswamy Srinivasan's work. In 1980, Srinivasan, working at IBM Research Lab, discovered that an ultraviolet Excimer laser could etch living tissue in a precise manner with no thermal damage to the surrounding area. He named the phenomenon Ablative Photodecomposition (APD).

The first patent for LASIK was granted by the U.S. Patent Office to Dr. Gholam A. Peyman on June 20, 1989, U.S. Patent #4,840,175, "Method for modifying corneal curvature," encompassing the surgical procedure in which a flap is cut in the cornea and pulled back to expose the corneal bed. The exposed surface is then ablated to the desired shape with an Excimer laser, after which the flap is replaced.

The LASIK technique was successfully applied in other countries before it arrived to the United States. The first FDA trial of the Excimer laser was started in 1989. The first use of the laser was to change the surface shape of the cornea, known as PRK. Dr. Joseph Dello Russo was one of the ten original FDA researchers who tested and got approval for the Visx laser. The LASIK concept was first introduced by Dr. Palliakaris in 1992 to the group of ten surgeons who were selected by the FDA to test the Visx laser at 10 centers in the U.S.

Dr. Palliakaris theorized the benefits of performing PRK after the surface was raised in a layer to be known as a flap performed by the Mikrokeratome developed by Barraquer in 1950. The blending of a flap and PRK became known as LASIK, which is an acronym. It quickly became very popular, since it provided immediate improvements in vision and involved much less pain and discomfort than PRK.

Today, faster lasers, larger spot areas, bladeless flap incisions, intraoperative pachymetry, and wavefront-optimized and -guided techniques have significantly improved the reliability of the procedure compared to that of 1991. Nonetheless, the fundamental limitations of Excimer lasers and undesirable destruction of the eye's nerves have spawned research into many alternatives to "plain" LASIK, including LASEK, Epi-LASIK, sub-Bowman’s Keratomileusis aka thin-flap LASIK, wavefront-guided PRK and modern intraocular lenses.

LASIK may one day be replaced by intrastromal ablation via all-femtosecond correction (like Femtosecond Lenticule Extraction, FLIVC, or IntraCOR), or other techniques that avoid weakening the cornea with large incisions and deliver less energy to surrounding tissues. The 20/10 (now Technolas) FEMTEC laser has recently been used for incision-less ablation on several hundred human eyes and achieved very successful results for presbyopia, with trials ongoing for myopia and other disorders.

Keratomileusis - Definition

Keratomileusis is the surgical improvement of the refractive state of the cornea performed by lifting up the front surface of the eye by forming a thin hinged flap under which the shape of the cornea is changed by using an excimer laser or other surgical device, and was developed by José Ignacio Barraquer, commonly called "the father of modern refractive surgery".

A microkeratome is usually used to cut the flap, but a femtosecond laser can also be used to make the flap. Before the advent of the excimer laser, keratomileusis was performed using a cryolathe, which froze thin flaps of corneal tissue and lathe cut them much like one cuts the lens of a pair of glasses. After thawing, these reshaped flaps were placed under the front flap to correct visual improvement.

LASIK is currently the only commonly performed keratomileusis procedure.

LASIK - Definition

LASIK or Lasik (laser-assisted in situ keratomileusis) is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism.

LASIK is performed by ophthalmologists using a laser. The procedure is generally preferred to photorefractive keratectomy, PRK, (also called ASA, Advanced Surface Ablation) because it requires less time for the patient's recovery, and the patient feels less pain overall. However, there are instances where a PRK/ASA procedure is medically justified as being a better alternative to LASIK.