Types of Refractive Surgeries

When most people think about refractive or corrective eye, surgeries they immediately think of only LASIK. However, 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.

Excimer Laser Procedures

LASIK (Laser Assisted In Situ Keratomileusis) 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. Eye drops 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 (Photorefractive Keratectomy) 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 (Laser Assisted Epithelial Keratomileusis) 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.

Implant Procedures

Intracorneal ring segments (ICRs) are semi-circular 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.

Phakic Intraocular Lenses (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. 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 contact lens or ICL, is surgically implanted inside the eye in front of the eye's natural lens. Since phakic IOLs involve entering the eye, unlike LASIK and PRK, the risk of complications is higher.

Thermal Procedures

Laser Thermal Keratoplasty (LTK) and Conductive Keratoplasty (CK) are generally used for people who are farsighted or who are over age 40 and have difficulty focusing on objects up close. 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

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.