Refractive surgery includes several surgical procedures designed to eliminate or reduce the need for glasses or contact lenses. These procedures correct refractive errors by changing the focus of the eye. Common procedures such as LASIK and PRK do this by reshaping the curve of the cornea (the clear front window of the eye) to move the point at which light is focused onto the retina (light-sensitive tissue lining the back of the eye). Procedures such as Conductive Keratoplasty use radio frequency energy to bend the cornea, and Phakic Intraocular Lenses place an artificial lens inside the eye to more accurately focus light onto the retina.
Four categories of refractive surgery include:
- Excimer laser procedures
- Implant procedures
- Thermal procedures
- Other refractive procedures
Excimer laser procedures
LASIK or laser-assisted in situ keratomileusis
LASIK combines two techniques of surgery to correct refractive error. First, a laser called a femtosecond laser or a surgical blade called a microkeratome creates a thin flap in the cornea. Next, an excimer laser sculpts the underlying cornea into a new shape to correct the refractive error. The flap is then repositioned and adheres on its own without sutures after only a few minutes. Eyedrops and/or ointment are placed in the eye to facilitate the healing process. Vision recovery typically is rapid, and there is little or no post-operative pain.
PRK or photorefractive keratectomy
PRK reduces low to high myopia, low to moderate hyperopia, and astigmatism. In PRK, the epithelium, the layer of cells covering the cornea, is removed and the excimer laser sculpts the cornea to correct refractive error. A contact lens is usually placed on the eye following the procedure to speed the epithelial healing process, which usually takes three to four days. Because PRK sculpts the outer surface of the cornea, patients experience some discomfort after surgery and recovery time lasts for a period of several weeks. PRK has been largely displaced by LASIK because LASIK provides less discomfort, faster vision recovery, and the ability to enhance or refine the outcome easily in as little as three months following the initial surgery. However, PRK is sometimes recommended instead of LASIK because it does not create a flap in the cornea and may be a better option for people who have thin corneas or whose occupation makes it more dangerous to have a flap.
LASEK or laser-assisted epithelial keratomileusis
LASEK corrects nearsightedness, farsightedness, and astigmatism. It is similar to PRK except that the surface layer (the epithelium) is replaced after surgery as a sort of bandage. Both PRK and LASEK are similar to LASIK in that they use the excimer laser to shape the cornea, but unlike LASIK neither procedure preserves the surface layers. PRK and LASEK are sometimes recommended instead of LASIK for people with thin corneas because they do not penetrate as deeply into the eye's surface.
In LASEK, the epithelium is loosened and peeled back to expose the cornea. The excimer laser then reshapes the cornea and the epithelium is placed back into position. Like LASIK, recovery time is rapid but discomfort is somewhat increased compared to LASIK.
Intracorneal ring segments
Intracorneal ring segments (ICRs) are semicircular pieces of plastic that are implanted within the cornea to treat mild forms of myopia. They also are sometimes used for other conditions affecting the cornea, such as keratoconus. They are designed to change the shape of your cornea, adjusting the focusing power of your eye so that light is focused onto your retina. The ICRs are inserted through a small incision near the upper edge of the cornea. The incision is closed with two small sutures that are usually removed two to four weeks after surgery.
Unlike laser eye surgeries, ICRs are reversible; if they are removed, your cornea usually returns to its original shape after a few weeks.
In the United States, ICRs are available under the brand name INTACS. Other brands exist in other areas.
Phakic intraocular lenses or phakic IOLs
Until recently, refractive surgery for some people with high degrees of myopia or hyperopia has not been an option. The amount of correction needed could not be achieved safely through surgical procedures involving reshaping the cornea. However, cataract surgery patients have been treated successfully with plastic lenses (called intraocular lenses or IOLs) implanted in the eye for many years. In cataract surgery, the natural lens is removed and the IOL is inserted in its place, replacing the focusing ability of the natural lens and also offering cataract patients correction for myopia and hyperopia.
Using a similar approach, a different style of IOL known as phakic IOL can be used to treat patients who do not have cataracts but need correction for refractive errors that exceeds the safe range of excimer laser procedures such as LASIK and can also be used for individuals with thin corneas, flat eyes or hyperopia. In order to preserve the focusing ability needed for reading vision, the natural lens is not removed from the eye. The phakic IOL, sometimes referred to as an Implantable Collamer Lens or ICL, is a small lens that is surgically implanted (under a topical or local anesthetic) in front of the natural lens, behind the iris through a small incision in the eye.
Laser thermal keratoplasty and conductive keratoplasty
LTK and CK are generally used for people who are farsighted or who are over age 40 and have difficulty focusing on objects up close (commonly referred to as presbyopia, or "aging eye"). These procedures do not involve making an incision but instead apply heat to cause the peripheral (outside edge) area of the cornea to tighten like a belt and make the central cornea steeper. The procedures cause little or no discomfort or irritation and vision improvement is almost instantaneous. However, unlike other types of refractive surgery such as LASIK, correction from LTK and CK may be temporary and re-treatment may be necessary later.
LTK and CK are approved for use by the FDA in the United States.
Other refractive surgery procedures
RK or radial keratotomy)
RK is a surgical procedure sometimes still used to correct low degrees of nearsightedness and astigmatism. Using a diamond scalpel, a calculated number of spoke-like cuts are made on the surface of the eye to flatten and reshape the cornea and reduce refractive error. RK has been largely displaced by LASIK, which is a more accurate procedure capable of correcting a larger range of myopia without structurally weakening the eye.
Monovision is a refractive surgery technique for people with presbyopia. Many people use reading glasses to correct presbyopia but only use the glasses for close-up vision and take them off when they need to see objects farther away. While there are refractive surgeries to reduce nearsightedness and farsightedness, these procedures do not help correct presbyopia. Monovision is a compromise that refractive surgery can offer people with presbyopia. The technique uses refractive surgery to enable one eye to focus at close proximity, and the other eye is left untreated or, if needed, treated to be able to focus at a distance. Having each eye configured for different focusing distances can reduce or eliminate the need for eyeglasses or contacts. It may seem difficult to get used to at first, but about six to eight weeks after the monovision procedure your brain is able to adjust to the different focusing ability of your eyes. A preoperative trial with contact lenses is a useful test to see if a patient will adapt to the intended refractive outcome.