LASIK: Improved Technology for Surgical Vision Correction

Zlatko Anguelov
John Sutphin, M.D.
University of Iowa
Department of Ophthalmology and Visual Sciences
First Published: 2001
Last Revised: September 2003
Peer Review Status: Internally Reviewed

History

Reshaping the cornea has been used to surgically treat refractive anomalies of the eye since Dutch physician Jans Lans did cornea incisions in the 1880s. The cornea should be flattened to correct myopia, made steeper to treat hyperopia, and made more spherical to correct astigmatism.

In the 1950s, reshaping--virtually, peeling up the cornea--was done using a modified skin dermatome, named keratome. A refinement of this technique was achieved by using a microkeratome in a surgery called automated lamellar keratectomy (ALK). During ALK, the knife first creates a flap and then makes a second pass across the cornea to excise a disc of corneal tissue. This disc is removed and replaced by the flap. Because of its low accuracy, ALK was used only to correct high levels of myopia.

In the late 1980s, laser-based photo-refractive keratectomy (PRK) was introduced to treat refractive errors. In PRK, reshaping is made by removing tissue from the surface of the cornea. It is more accurate and is successful in cases with low to moderate refractive defects.

New facts

Excimer lasers, a class of ultraviolet lasers, brought even more accuracy to refractive surgery. Excimer lasers are used in LASIK (Laser in-Situ Keratomileusis). Unlike PRK, LASIK corrects vision by reshaping the cornea beneath its surface. In LASIK, the idea used in ALK since 1949--first cutting out a flap and then removing parts of the underlying corneal tissue--re-entered ophthalmologic surgery at a new, much higher level of accuracy.

One pulse of the excimer laser removes 0.25 microns of tissue, thus enabling the surgeon to reshape the cornea with unheard-of precision. Often, only 50 microns, or half the transversal diameter of a human hair, need to be removed to achieve the proper amount of correction. The excimer laser produces a non-thermal light beam as most of its heat is dissipated into the air. This makes it ideal for corneal surgery because it eliminates the possibility of thermal damage to the surrounding tissue.

Two types of excimer lasers are available for refractive procedures: broad-beam lasers and scanning lasers. A broad-beam laser generates a relatively large beam (diameter from 6 to 8 millimeters) and allows for a fast ablation of corneal layers. In contrast, scanning lasers use small beams that remove dots of tissue in a confluent way until the desired ablation is achieved. A disadvantage of the scanning lasers is the longer procedure time. Some lasers use a combination of broad-beam and scanning to remove larger amounts followed by smaller amounts to smooth and refine the ablation.

Practice

In the first step of LASIK, the microkeratome is used to cut out a corneal flap representing the outermost 20 percent of the cornea thickness. The flap is then lifted and reflected to the side. In the next step, the computer-guided excimer laser ablates as much tissue from the corneal stroma as is required to correct the eye's vision. Then, the flap is laid back into its original position. Thus, the flap serves as a protective layer of tissue, greatly reducing the surface area that will need to heal. It also reduces the chance for the area ablated by the laser to be exposed to healing factors in the tear film and epithelial layer. Because the cornea bonds quickly, healing is faster in the absence of those factors, and stitches are not required. Consequently, LASIK runs less risk of developing corneal haze than PRK.

Compared with PRK, the patient benefits provided by LASIK are numerous: much less or no postoperative discomfort; a shorter post-op regimen (three days to one week vs. four months of eye drops with PRK); no need to wear post-op contact lenses to reduce pain; fast visual recovery rarely blurred by haze; both eyes operated on in one surgery day; and final vision obtained within weeks rather than months. PRK, however, does not require a flap and can be used in naturally thinner corneas. LASEK is a hybrid procedure that uses a flap of epithelium only to speed healing and reduce haze and discomfort from PRK type of ablation.

LASIK is performed at UI Hospitals and Clinics to correct myopia (in the range -1 to -14 with up to 5 d of astigmatism) and hyperopia (in the range +1 to + 5 with up to 5 d of astigmatism). Vision is corrected to 20/20 in 80% of patients, and to 20/40 in 98% of patients, which is the legal driving limit in most states, including Iowa.

The newest form of LASIK is custom ablation for treating up to -6 diopters of of myopia and 3 diopters of astigmatism. This wavefront-guided treatment uses a special device to measure the patient's eyes for a custom treatment that reduces unwanted side effects and may improve final vision without glasses.

LASIK makes the benefits of refractive surgery more tangible than ever before. It eliminates the dependence on glasses/lenses and thus increases the individual's safety during outdoor activities or sport. Moreover, the 24-hour corrected vision and improved convenience are achieved with as little as 1% risk of side effects during or post surgery.

See related Provider Textbooks about Ophthalmology.

See related Provider Topics Eyes and Vision, Laser Eye Surgery, Ophthalmology or Procedures and Therapies.

See related Patient Textbooks about Ophthalmology.

See related Patient Topics Eyes and Vision, Ophthalmology or Procedures and Therapies.

All contents copyright © 1992-2004 the Author(s) and The University of Iowa. All rights reserved.

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