What is LASIK?

What is LASIK?

LASIK stands for laser in situ keratomileusis, which means using a laser underneath a corneal flap (in situ) to reshape the cornea (keratomileusis). This procedure utilizes a highly specialized laser (excimer laser) designed to treat refractive errors, improve vision, and reduce or eliminate the need for glasses or contact lenses. This laser procedure alters the shape of the cornea, which is the transparent front covering of the eye. Though the excimer laser had been used for many years before, the development of LASIK is generally credited to Ioannis Pallikaris from Greece around 1991.

How does LASIK work?

During the LASIK procedure, a specially trained eye surgeon first creates a precise, thin hinged corneal flap using a microkeratome. The surgeon then pulls back the flap to expose the underlying corneal tissue, and then the excimer laser ablates (reshapes) the cornea in a unique pre-specified pattern for each patient. The flap is then gently repositioned onto the underlying cornea without sutures.

What is refractive error?

In the human eye, the front surface (cornea) and lens inside the eye form the eye's "focusing system" and are primarily responsible for focusing incoming light rays onto the surface of the retina, much like the lenses of a camera focus light onto the film. In a perfect optical system, the power of the cornea and lens are perfectly matched with the length of the eye and images are in focus; any mismatch in this system is called a refractive error, and the result is a blurred image at some location.

What are the primary types of refractive error?

Myopia (nearsightedness): In people with myopia, the mismatch in focusing power and eye length causes distant objects to be blurry and near objects to be clearer.
Hyperopia (farsightedness): In people with hyperopia, the mismatch in focusing power and eye length causes near objects to be blurry and distant objects to be relatively clearer.
Astigmatism: In people with astigmatism, either the corneal or lens shape is distorted, causing multiple images on the retina. This causes objects at all distances to appear blurry. Many people have a combination of either myopia or hyperopia with astigmatism.

How do glasses or contacts improve vision in people with refractive errors?

Glasses or contact lenses are used to compensate for the eye's refractive error by bending light rays in a way that complements the eye's specific refractive error. In contrast, LASIK and other forms of refractive surgery are intended to correct the eye's refractive error to reduce the need for other visual aids. 

What happens to vision when we age?

During our youth, the natural lens has the ability to change shape and power. This allows us to focus on close objects through a process of lens power change called accommodation. As we age, the natural lens becomes stiffer and loses the ability to change shape. This is termed presbyopia, which is the loss of accommodation, and the need for reading glasses, bifocals, or other visual aids to facilitate near work. LASIK cannot directly "fix" accommodation, but there are a variety of strategies that can be successful, including blended vision or monovision, in which one eye is corrected for better distance vision and one eye is corrected for better near vision.

Are there different types of LASIK?

There are a variety of different types of lasers used in ophthalmology. All LASIK procedures are performed with a specific type of laser (excimer laser), so in one sense, all LASIK procedures are similar. However, there are a variety of different laser manufacturers, including Visx, Wavelight, Alcon, Bausch & Lomb, and Nidek, among others, that have all designed specific excimer lasers. Further, there are different types of laser ablations that can be performed (see below), including conventional laser treatments, wavefront-optimized treatments, and wavefront-guided treatments. Finally, a completely different type of laser (femtosecond laser) can be used instead of a mechanical microkeratome to create the LASIK (corneal) flap.

What is conventional LASIK?

Conventional LASIK is the ablation pattern available on most lasers that treats directly based upon the patient's glasses prescription, with fixed treatment parameters for each patient. This type of treatment is effective for most patients but can result in more visual aberrations such as glare, halos, and night vision issues than other forms of laser treatment. 

What is wavefront-optimized LASIK?

Wavefront-optimized LASIK is the type of laser treatment available on the Wavelight laser. This treatment is also based on the patient's glasses prescription, but also takes into account corneal curvature and thickness, and applies laser energy in a unique fashion in the periphery of the cornea. This laser has been found to reduce the aforementioned complications such as glare, halos, and other nighttime visual aberrations that can occasionally occur with conventional treatments.

What is wavefront-guided LASIK?

Wavefront-guided LASIK, also referred to as custom LASIK or wavefront LASIK, is similar to conventional LASIK, except that in addition to treating a patient's basic refractive error, specific alterations in a patient's eye (high order aberrations) can also be treated. In wavefront-guided LASIK, special mapping is performed prior to surgery to identify any small irregularities in the patient's optical system. When these irregularities are severe, they can affect vision quality, contrast sensitivity, and night vision. When significant irregularities in a patient's wavefront mapping are found, wavefront-guided LASIK can be used, and the treatment will be based on the wavefront-map generated.

What other types of refractive surgery are available?

Other types of refractive surgery are available and may be more appropriate than LASIK for certain individuals.
Advanced surface ablation: There are a variety of other techniques that utilize the excimer laser to reshape the cornea in much the same way as LASIK, but without the creation of a corneal flap. These are generically termed advanced surface ablation (ASA) and include photorefractive keratectomy (PRK), laser subepithelial keratomileusis (LASEK), and epipolis laser in situ keratomileusis (Epi-LASIK). All of these techniques involve first removing the most superficial corneal layer (epithelium) and then performing excimer laser ablation.
Phakic intraocular lenses: For patients with extreme myopia, LASIK and advanced surface ablation are not reasonable options. In these cases, a phakic intraocular lens may be used. This lens is implanted inside the eye and can effectively treat nearsightedness up to -20 diopters.
Conductive keratoplasty: Conductive keratoplasty (CK) is a technique that can be used for the temporary correction of hyperopia or presbyopia. CK involves using radiofrequency waves in the peripheral cornea to cause peripheral corneal shrinkage and central steepening. This procedure is very safe, but its effect is often not long-lasting, and regression is common after a few years.
Intracorneal ring segments: Intacs (Addition Technology, Inc.) are approved for the correction of low myopia and for patients with keratoconus in the U.S. Intacs are micro-thin plastic segments that are implanted into the peripheral cornea in order to flatten the cornea centrally. Once implanted, the rings generally cannot be felt by the patient. These rings can be removed, and their effect is usually completely reversible. They are only able to correct up to -3 diopters of myopia, and visual recovery is generally slower and less predictable than LASIK.