Over the past 25 years, surgical techniques, tools, and procedures for vision correction have evolved rapidly.
Radial Keratotomy (RK), used in the United States primarily during the 1980s, involved cutting spoke-like incisions to flatten the eye's surface mainly to correctnearsightedness. But results, especially long-term, created problems for some individuals. Significant glare, regression, fluctuating vision, and other side effects such as night vision problems were common in patients who had RK for higher prescription strengths, while such side effects were less frequent in patients with lower prescriptions. RK is now virtually obsolete as a primary vision correction procedure for these reasons and because of advances in laser vision correction procedures.
Photorefractive Keratectomy (PRK) was the first successful laser vision correction procedure used to remove(ablate) tissue directly from the eye's surface to change the curvature of the cornea. PRK, also known as surface ablation, was performed outside the United States during the 1980s and received FDA approval in 1995. PRK is still commonly used, but LASIK (see below) is by far the most popular laser procedure today. However, PRK has made somewhat of a comeback in recent years because of studies indicating that PRK and LASIK produce similar outcomes. Also, nerve regeneration in the eye's surface appears to take place faster with PRK than with LASIK following a procedure, which could have implications for reducing dry eye and other complications that might occur until the healing process is complete.
Because PRK is a surface procedure, there also is no risk of surgical flap complications. PRK does not involve creating a thin, hinged flap on the eye's surface, as occurs with LASIK. PRK also appears to be a safer procedure in cases when a person's cornea may be too thin for LASIK surgery.
Laser-Assisted in situ Keratomileusis
Laser-Assisted in situ Keratomileusis (LASIK) is like PRK, except that a thin, hinged flap is made in the eye's surface. This flap is lifted, and then laser energy is applied underneath to reshape the eye. The flap is replaced and functions as a natural bandage. LASIK's main advantage over PRK is that there is little or no discomfort immediately after the procedure, and vision is usually clear within hours rather than days. Different forms of LASIK exist, many that depend on how the flap is created:
- LASEK involves creating an ultra-thin hinged flap in the thin outer covering(epithelium) of the eye and floating it away from the eye's surface with alcohol so that laser reshaping of the eye can occur.
- Epi-LASIK is like LASEK, except that a special cutting tool is used to lift the flap.
- Bladeless, Blade-Free, or All-Laser LASIK involves use of another laser rather than a mechanical cutting tool to create the flap in LASIK. Because the laser used for this purpose originally was made and marketed by IntraLase Corp., all-laser LASIK was sometimes also called IntraLASIK. In 2007, Advanced Medical Optics (now Abbott Medical Optics) obtained the IntraLase technology and integrated it into the company's CustomVue excimer laser platform (iLASIK). Other brands of bladeless LASIK now are available, including the Ziemer Femto LDV, marketed as zLASIK.
- Wavefront LASIK or PRK (also known as wavefront-guided, wavefront-assisted, or custom LASIK/PRK) incorporates ultra-modern analysis, known as wavefront, to measure precisely how light travels through the eye.Excimer lasers with built-inwavefront analysis can detect and automatically adjust for subtle vision errors when laser energy is applied to reshape the cornea. Studies suggest wavefront-guided LASIK helps maintain contrast sensitivity and reduces the risk of night glare after LASIK surgery, explained in our Q&A about custom LASIK.
Conductive Keratoplasty (NearVision CK by Refractec) uses a tiny probe and low heat radio waves to apply "spots" around the periphery of the eye's clear front surface. This relatively non-invasive method steepens the cornea, to provide near vision correction for people who are farsighted. CK also can be used to correctpresbyopia or enhance near vision for people who have had LASIK orcataract surgery. CK received initial FDA approval in 2002.
Implantable Lenses (Visian ICL and Verisyse)
Implantable Lenses (Visian ICL and Verisyse), similar to contact lenses, first received FDA approval in 2004. These surgically implanted lenses primarily are considered appropriate for higher levels of nearsightedness. When implantable lenses are used, your eye's natural lens is left in place. Both of these lenses have a long track record of use, including more than 13 years in Europe.
Refractive Lens Exchange
Refractive Lens Exchange is another non-laser, internal eye procedure. RLE is much like cataract surgery. But instead of removing the eye's natural lens that has grown cloudy due to cataract formation, RLE involves removing a clear natural lens and replacing it with an artificial lens of a different shape, usually to reduce or eliminate high degrees of farsightedness. RLE also might be considered as an option for correcting other types of vision problems, such as nearsightedness. But RLE has a higher risk of complications, compared with other vision correction procedures. For these reasons, RLE typically is used only in cases of severe vision correction needs.