Encyclopedia - Refractive Surgery

What is refractive surgery?
Who are the candidates for refractive surgery?
What are the types of refractive surgery?

What is refractive surgery?

Refractive surgery is a general term that refers to any surgery that changes the shape of the cornea or the way the eye focuses light internally. The goal of refractive surgery is to reduce or eliminate nearsightedness (myopia), astigmatism, or farsightedness (hyperopia) and lessen a person's dependence on eyeglasses and contact lenses. There are several refractive procedures being performed today.

For a person to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina. The retina begins the process of using the optic nerve to convert those light rays into images the brain understands, similar to how a camera takes a picture. The cornea and lens in the eye serve as the camera lens. The retina is like the film. If the image is not in focus, the end result is a blurred image. When this happens, eye care professionals term it a refractive error.

Who are candidates for refractive surgery?

In general, candidates for laser surgery are more than 18 years of age, have not had a significant increase in their prescription in the past 12 months, have a healthy cornea, and have a diagnosed refractive error. People with certain medical conditions such as eye disease or pregnancy may not prove to be good candidates.

It is important to note, however, that despite the successful results in a majority of laser surgery patients, it does not restore "perfect" vision in every case. It can not correct the condition called presbyopia - a part of the normal aging process of the eyes that require the use of reading glasses.

To make an informed decision on what type of refractive surgery is best, patients are advised to contact their eye care professional for a thorough evaluation and details on each option.

What are the types of refractive surgery?

Popular today and receiving a lot of publicity is laser eye surgery. The Excimer laser, a highly precise type of laser system, has been adapted specifically for surgical use on the human eye. It is now widely used in optical practices throughout the world to correct refractive errors. Today, after more advances and improvements, the laser offers precision with better control and safety.

The numerous types of refractive surgery are described here, in alphabetical order.

Clear Lens Extraction (CLE)
The CLE procedure is virtually the same as for the removal of cataracts. It involves removing the eye's natural crystalline lens and replacing it with a plastic prescription lens implant. The only difference is that the natural lens being replaced by the CLE procedure is clear, while a cataract lens is cloudy.

Implantable Contact Lens (ICL)
With the ICL procedure, a prescription lens resembling a contact lens is surgically inserted between the iris and the natural lens of the eye. This procedure can be used to correct virtually the same refractive vision problems that external contact lenses are used for, but results to date indicate that ICL works best for high degrees of farsightedness and nearsightedness.

Intracorneal Lens Implants
A tiny plastic lens, similar to a contact lens, is implanted inside the cornea within the corneal tissue to correct problems of nearsightedness. This procedure is in the investigation stage, as is a similar procedure for the treatment of presbyopia, the vision problem that results from the loss of flexibility of the natural lens because of the normal aging process.

Intrastromal Corneal Ring Segment (ICRS)
The ICRS procedure involves the surgical implantation of two tiny plastic arcs (ring segments) in the peripheral area of the cornea. This serves to flatten the cornea to the degree required to correct a myopic (nearsighted) condition. The thickness of the ring segments determines the degree of flatness. If necessary, the segments can be removed and replaced with larger or smaller implants or removed permanently.

Laser In-Situ Keratomileusis (LASIK)
LASIK offers a number of advantages over the other forms of refractive surgery techniques because it is performed using corneal tissue to protect the laser-flattened part of the eye.

To undergo LASIK surgery, the patient's eye is numbed with eye drops, and an eyelid holder is placed between eyelids to prevent blinking. The laser is computer-controlled and programmed by an eye care professional to customize the surgery to a patient's own unique corneal shape and refractive error. Next, the surgeon uses a specialized instrument called a microkeratome to make a protective flap in the cornea which is folded out of the way to expose the underlying corneal tissue. Patients sometimes feel pressure at this point. The laser then reshapes the cornea, and the protective flap is folded back in place where it bonds and seals itself naturally without the need for stitches.

As a result, there is less surface to heal, less risk of post-surgery discomfort, and less need for post-operative medications. Vision returns faster, usually within the same day. LASIK surgery is highly effective. Most LASIK patients are able to pass a driver's license test without corrective lenses.

Laser Thermal Keratoplasty (LTK)
The LTK procedure uses a Holmium laser to shrink the peripheral area of the cornea in order to make the shape of the cornea steeper and correct mild to moderate cases of farsightedness. It is also being used to a limited degree to treat some cases of astigmatism.

Photorefractive Keratectomy (PRK) PRK is the first laser corneal refractive surgery. An outpatient corneal surgery, PRK can reduce or correct mild to moderate myopia. A laser is used to precisely reshape the cornea with intense, focused light. No incisions are made in laser surgery.

The PRK laser is computer-controlled and programmed by an eye care professional to customize the surgery to a patient's own unique corneal shape and refractive error. The laser light flattens the front surface of the cornea by removing micro-thin layers of tissue. Removing the layers, however, disrupts the surface and consequently, patients must normally wear a protective contact lens for a few days following surgery to help heal the surface. PRK is known to produce excellent results. The speed of recovery is a little slower than the recovery period following LASIK procedure.

Most of the people who have had PRK report they no longer need to wear glasses or contacts. A great portion of patients who had PRK can see 20/20 or better without corrective lenses. Ninety-five percent can see at least 20/40, which is the measurement required for a driver's license.

Radial Keratotomy (RK)
Radial Keratotomy consists of a surgeon making small incisions, called keratotomies, in the cornea to change its shape. RK surgery is an outpatient procedure, which can usually be completed in approximately 30 minutes.

Patients receive medication to help them relax and are given eye drops to numb the eye. First, the surgeon marks the part of the cornea a person actually sees through, to avoid making incisions in this area. Next, the surgeon measures the thickness of the cornea to determine how deep to make the incisions. Last, the surgeon makes the incisions to help flatten the cornea and reduce or eliminate the refractive error.

Patients may feel some pain following RK surgery but are given eye drops and medications to help. For some days, patients' eyes may feel gritty, sensitive to light, and appear red. Antibiotic eye drops help guard against infection. In comparison to other refractive surgery being done today, the cornea after RK surgery heals more slowly because of the small, but sometimes deep, incisions made.

Though rare, RK surgery may cause cataract development, pain, infection, rupture of the incisions from eye injury or trauma, and vision loss.