LASIK or Lasik (; "laser-assisted in situ keratomileusis"), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hypermetropia, and astigmatism. LASIK surgery is performed by an ophthalmologist who uses a femtosecond laser or a microkeratome to create a corneal flap to expose the corneal stroma and then an excimer laser to reshape the corneal stroma in order to improve visual acuity.
LASIK is very similar to another surgical corrective procedure, photorefractive keratectomy (PRK), and LASEK. All represent advances over radial keratotomy in the surgical treatment of refractive errors of vision. For people with moderate to high myopia or thin corneas which cannot be treated with LASIK or PRK, the phakic intraocular lens is an alternative.
As of 2018, roughly 9.5 million Americans have had LASIK and, globally, between 1991 and 2016, more than 40 million procedures were performed. However, the procedure seemed to be a declining option as of 2015.
Process In March 2009, the FDA officially recognized the new LASIK standard from The American National Standards Institute (ANSI), entitled "Laser Systems for Corneal Reshaping".
A detailed pre-operative screening will assess corneal thickness, shape, and refractive error, ensuring the patient is a suitable candidate. During the surgery, a surgeon uses a femtosecond laser or a microkeratome blade to create a thin corneal flap, which is then carefully folded back to expose the underlying tissue. An excimer laser precisely reshapes the stromal layer of the cornea, removing microscopic amounts of tissue to correct refractive errors. This step is guided by a pre-determined surgical plan tailored to the patient's specific visual needs. After the cornea is reshaped, the flap is repositioned, serving as a natural bandage that adheres without the need for stitches. The entire procedure typically takes 10–15 minutes per eye and offers minimal discomfort and rapid recovery, allowing most patients to return to normal activities within a day or two.
Preoperative procedures
Pre-operative examination and education In the United States, the US Food and Drug Administration (FDA) has approved LASIK for people 18 years of age and older, but the American Academy of Ophthalmology recommends people wait until age 21 because vision needs to stabilize. More importantly the patient's eye prescription should be stable for at least one year prior to surgery. The patient may be examined with pupillary dilation and education given prior to the procedure. Before the surgery, the patient's corneas are examined with a pachymeter to determine their thickness, and with a topographer, or corneal topography machine, to measure their surface contour. Using low-power lasers, a topographer creates a topographic map of the cornea. The procedure is contraindicated if the topographer finds difficulties such as keratoconus. The preparatory process also detects astigmatism and other irregularities in the shape of the cornea. Using this information, the surgeon calculates the amount and the location of corneal tissue to be removed. The patient is prescribed and self-administers an antibiotic beforehand to minimize the risk of infection after the procedure and is sometimes offered a short acting oral sedative medication as a pre-medication. Prior to the procedure, anaesthetic eye drops are instilled. Factors that may rule out LASIK for some patients include large pupils, thin corneas and extremely dry eyes.
Operative procedure
LASIK permanently changes the shape of the cornea, the clear covering of the front of the eye, using an excimer laser. A mechanical microkeratome (a blade device) or a laser keratome (femtosecond laser) is used to cut a flap in the cornea. A hinge is left at one end of this flap. The flap is folded back revealing the corneal stroma, the middle section of the cornea. Pulses from a computer-controlled laser (excimer laser) vaporize a portion of the stroma and the flap is replaced.
Performing the laser ablation in the deeper corneal stroma provides for more rapid visual recovery and less pain than the earlier technique, photorefractive keratectomy (PRK).
Postoperative care Patients are usually given a course of antibiotic and anti-inflammatory eye drops, which are continued in the weeks following surgery. Patients are told to rest and are given dark eyeglasses to protect their eyes from bright lights and occasionally 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. Occasionally after the procedure a bandage contact lens is placed to aid the healing, and typically removed after 3–4 days.
Wavefront-guided Wavefront-guided LASIK is a variation of LASIK surgery in which, rather than applying a simple correction of only long/short-sightedness and astigmatism (only lower order aberrations as in traditional LASIK), an ophthalmologist applies a spatially varying correction, guiding the computer-controlled excimer laser with measurements from a wavefront sensor. The goal is to achieve a more optically perfect eye, though the result still depends on the physician's success at predicting changes that occur during healing and other factors that may have to do with the regularity/irregularity of the cornea and the axis of any residual astigmatism. Another important factor is whether the excimer laser can correctly register eye position in 3 dimensions, and to track the eye in all the possible directions of eye movement. If a wavefront guided treatment is performed with less than perfect registration and tracking, pre-existing aberrations can be worsened. In older patients, scattering from microscopic particles (cataract or incipient cataract) may play a role that outweighs any benefit from wavefront correction.Walsh MJ. Is the future of refractive surgery based on corneal topography or wavefront? "Ocular Surgery News". 1 August 2000, page 26.Walsh MJ. Wavefront is showing signs of success, but can it do it alone? Ocular Surgery News. 1 September 2000, page 41.EW Dialogue: the future of wavefront refraction as a diagnostic tool. "EyeWorld". May 2000, pages 64 and 65.
When treating a patient with preexisting astigmatism, most wavefront-guided LASIK lasers are designed to treat regular astigmatism as determined externally by corneal topography. In patients who have an element of internally induced astigmatism, therefore, the wavefront-guided astigmatism correction may leave regular astigmatism behind (a cross-cylinder effect). If the patient has preexisting irregular astigmatism, wavefront-guided approaches may leave both regular and irregular astigmatism behind. This can result in less-than-optimal visual acuity compared with a wavefront-guided approach combined with vector planning, as shown in a 2008 study.
The "leftover" astigmatism after a purely surface-guided laser correction can be calculated beforehand, and is called ocular residual astigmatism (ORA). ORA is a calculation of astigmatism due to the noncorneal surface (internal) optics. The purely refraction-based approach represented by wavefront analysis actually conflicts with corneal surgical experience developed over many years.
The pathway to "super vision" thus may require a more customized approach to corneal astigmatism than is usually attempted, and any remaining astigmatism ought to be regular (as opposed to irregular), which are both fundamental principles of vector planning overlooked by a purely wavefront-guided treatment plan. This was confirmed by the 2008 study mentioned above, which found a greater reduction in corneal astigmatism and better visual outcomes under mesopic conditions using wavefront technology combined with vector analysis than using wavefront technology alone, and also found equivalent higher-order aberrations (see below). Vector planning also proved advantageous in patients with keratoconus.
No good data can be found that compare the percentage of LASIK procedures that employ wavefront guidance versus the percentage that do not, nor the percentage of refractive surgeons who have a preference one way or the other. Wavefront technology continues to be positioned as an "advance" in LASIK with putative advantages; however, it is clear that not all LASIK procedures are performed with wavefront guidance.
Still, surgeons claim patients are generally more satisfied with this technique than with previous methods, particularly regarding lowered incidence of "halos", the visual artifact caused by spherical aberration induced in the eye by earlier methods. A meta-analysis of eight trials showed a lower incidence of these higher order aberrations in patients who had wavefront-guided LASIK compared to non-wavefront-guided LASIK. Based on their experience, the United States Air Force has described WFG-Lasik as giving "superior vision results".
Topography-assisted Topography-assisted LASIK is intended to be an advancement in precision and reduce night-vision side effects. The first topography-assisted device received FDA approval 13 September 2013.
History
Barraquer's early work In the 1950s, the microkeratome and keratomileusis technique were developed in Bogotá, Colombia, by the Spanish ophthalmologist José Barraquer. In his clinic, he would cut thin (one hundredth of a mm thick) flaps in the cornea to alter its shape. Barraquer also investigated how much of the cornea had to be left unaltered in order to provide stable long-term results.
Excimer lasers in eye surgery In 1979, IBM Research associates Rangaswamy Srinivasan, Samuel E. Blum, and James J. Wynne were experimenting with the lab's new excimer laser, which was capable of producing intense beams of ultraviolet light. The trio discovered that if the laser's wavelength was set to 193 nm, it could etch organic materials such as plastics or living tissue to a high degree of precision while causing no damage to the surrounding area. The procedure was named ablative photo-decomposition.
Srinivasan, Blum, and Wynne published their findings in 1982. A year later, Steven Trokel, an ophthalmology professor at Columbia University, approached Srinivasan about the possibility of using his excimer laser for eye surgery. The two men, along with IBM Research associate Bodil Braren, conducted a series of experiments testing the lasers on enucelated cow eyes. They found that excimer lasers could create incisions in the cornea with the same degree of precision and accuracy as the radial diamond knives used in bladed radial keratotomy. In fact, Trokel described the laser incisions as having "remarkably smooth edges".
These findings were particularly exciting to Iranian-American ophthalmologist Gholam A. Peyman. Peyman, a University of Illinois Chicago professor working at Illinois Eye and Ear Infirmary, had previously experimented with using CO2 lasers to modify corneal curvature. However, he had found they caused too much damage to surrounding tissue to be practical. On learning of the IBM team's findings in 1982, he realized this damage could be avoided with excimer lasers. At the time, excimer lasers were expensive and rare, so Peyman did not have access to one to test this hypothesis. Nevertheless, he applied for a patent for the procedure in 1985, which was granted by the US patent office in 1989. Peyman was later able to collaborate with the Physics Department at the University of Helsinki, who did possess an excimer laser, to test his procedure. The team found that the excimers lasers were able to successfully carry out the procedure, just as Peyman had predicted.
Implementation in the United States