Corrective Eye Surgeries for Refractive Errors

Eye Surgery for Correcting or Improving Refractive Errors

Clear vision depends on how well the cornea and lens permit light rays to fall onto the retina. Light rays must be refracted (bent) to focus on the retina. The retina is the light-sensitive nerve layer that lines the back of the eye, which creates impulses from the light rays that are sent through the optic nerve to the brain.

If  the cornea or eye shape is abnormal, vision can become blurry because light does not fall properly on the retina. Called a refractive error, an abnormal cornea shape can often be corrected by refractive eye surgery, which, in turn, corrects the vision problem. Refractive errors can include myopia (nearsightedness), hyperopia (farsightedness), astigmatism (an irregularly shaped cornea which causes blurring), and presbyopia (similar to hyperopia, but mainly causes blurring for near or close vision tasks).

The goal of most refractive eye surgery is to reduce or eliminate a person's dependency on eyeglasses or contact lenses. Refractive eye surgery is not for everyone. One type of surgery may be more suitable for one person than another. Always consult an eye surgeon for a diagnosis and to discuss which type of surgery, if any, may be appropriate for you.

Historically, there are have been many types of corrective eye surgery procedures for refractive errors, including, but not limited to:

• Laser In-Situ Keratomileusis (LASIK)
• Wavefront-Guided LASIK (Custom LASIK)
• Photorefractive Keratectomy (PRK)
• Radial Keratotomy (RK)
• Astigmatic Keratotomy (AK)
• Automated Lamellar Keratoplasty (ALK)
• Laser Thermal Keratoplasty (LTK)
• Conductive Keratoplasty (CK)
• Intracorneal Ring (Intacs)

What is LASIK surgery?

LASIK, or Laser In-Situ Keratomileusis, surgery may be used to correct nearsightedness, farsightedness and astigmatism. When a person has any of these eye conditions, his or her eye is too long (nearsightedness), or too short(farsightedness) or the cornea is the wrong curvature resulting in an incorrect focusing power. This results in light rays entering the eye coming into focus without precisely hitting the retina, resulting in blurry vision when looking in the distance.

The LASIK surgery procedure, which should be performed by an experienced LASIK surgeon, involves a type of laser eye surgery which reshapes the cornea using an excimer laser. LASIK has replaced most of the other refractive eye surgery techniques because it provides minimal discomfort and a quick visual recovery. For those patients with more complex refractive errors a newer LASIK technology, called Wavefront-Guided LASIK or Custom LASIK, provides an advanced method for measuring optical distortions in the eye. The Eye Surgery Education Council states that LASIK surgeons can now use this technology as a roadmap to evaluate the eye by measuring how light is distorted as it passes into the eye and then is reflected back. This creates an optical map of the eye, highlighting individual imperfections. In addition, the wavefront technology allows the surgeon to tailor the laser beam settings for a more precise procedure. This provides a patient sharper, better quality vision as well as a reduction in nighttime vision difficulties.
 
How is LASIK eye surgery performed?

Although each procedure varies slightly, in general, LASIK eye surgery involves using a computer-controlled excimer laser (a cold, ultraviolet laser) and a microkeratome (a surgical instrument). With these instruments, the surgeon creates a thin flap in the center of the cornea to allow the laser to remove a microscopic layer of tissue. By removing the tissue, the cornea is reshaped in order to correct the refractive error. The flap, which is replaced without using sutures, adheres back to the cornea within minutes.
 
Recovery after LASIK eye surgery:

In most cases, recovery from LASIK surgery is fast and involves minimal discomfort. Mild pain relievers may be recommended by your  LASIK surgeon to relieve discomfort during the first day after surgery. Patients typically use eyedrops for a week after the procedure.
 
Possible side effects of LASIK surgery:

Generally, LASIK has a high success rate. However, side effects do occur. The following are the most common side effects and complications. Each individual may experience side effects differently. Side effects may include:

• Dry eyes (during the healing process)
• Eye Discomfort (mostly during the first 24 hours following surgery)
• Irregular astigmatism, which can decrease the corrected vision (astigmatism means blurring caused by an irregularly shaped cornea)
• Glare, halos or night vision problems
• Overcorrected or undercorrected vision
• Inability to wear contact lenses in the future
• Loss of the corneal flap
• Scarring
• Infection
• Vision loss

Benefits of LASIK surgery:

For most candidates, LASIK surgery usually involves little pain and recovery is rapid. Other benefits may include:

• LASIK can correct a wide range of refractive errors including nearsightedness, farsightedness and astigmatism of varying degrees.
• LASIK can be repeated to correct the vision further.
• The eyes stabilize within three months after LASIK surgery.
• The eye is not structurally weakened.
• LASIK usually causes little or no scarring of the cornea.
• Post-operative care is usually limited to using eye drops for a week after surgery.

What is photorefractive keratectomy (PRK) surgery?

Photorefractive keratectomy, or PRK, uses the same excimer laser used in LASIK surgery and is performed to reshape the cornea in an attempt to correct common refractive errors as well. According to the US Food and Drug Administration (FDA), PRK has a 95 percent success rate. Only about 15 percent of patients need glasses, occasionally, following surgery.
 
How is PRK performed?

Although each procedure varies slightly, in general, PRK surgery involves an excimer laser beam reshaping the cornea by removing microscopic amounts of tissue from the outer surface of the cornea rather than from beneath a flap as in LASIK. The procedure, which generally only takes a few minutes, uses a computer which maps the eye's surface and calculates the required corneal change. PRK may also be performed as a custom wavefront guided procedure if necessary.
 
Possible side effects of PRK surgery:

Generally, PRK surgery has a high success rate. However, side effects do occur. Because the corneal surface is reshaped, it takes several weeks to heal. In addition, there is some eye discomfort following the surgery that may last for several weeks. The following are the most common side effects and complications. Each individual may experience side effects differently.
 
Side effects may include:

• Mild corneal haze (following surgery)
• Glare or halos around light (this side effect may be present for months following the procedure)

Who is a potential candidate for LASIK or PRK eye surgery?

According to the US Food and Drug Administration (FDA), potential candidates for corrective laser eye surgery must meet the following criteria. However, it is advised that potential candidates consult his/her eye surgeon before undergoing any type of corrective eye surgery. The criteria include:

• The candidate must be at least 18 years old and have a consistent stable prescription to ensure the eyes have finished growing and changing.
• The candidate must have a refractive error that is within the range treatable with the laser.
• The candidate must be free of eye disease, problems with the retina, or scarring of the cornea.
• The candidate must have the financial ability to pay for laser eye surgery, since insurance usually does not not cover the procedure.
• The candidate must be aware of all the side effects, risks and benefits of the surgery. Candidates should also be aware of the alternative treatment options available.

What is radial keratotomy (RK) surgery?

Radial Keratotomy, or RK, is a procedure also used to correct myopia (nearsightedness). The procedure involves making microscopic, radial incisions (keratotomies) in the cornea to alter the curvature of the cornea, thus, correcting light refraction. Hundreds of thousands of people who qualified for this type of surgery have undergone the procedure successfully since its introduction to the US in 1978, however in general it has all but been abandoned in favor of laser eye surgery.
 
How is RK surgery performed?

Although each procedure varies slightly, in general, RK surgery involves an eye surgeon cutting (with a calibrated diamond scalpel) radial- or spoke-like incisions into the cornea outside of the center of the cornea (also called the optical zone, which is the area where a person sees through). Due to pressure inside the eye, the incisions cause the center, or optical zone of the cornea to flatten, reducing refraction.
 
Possible side effects of RK surgery:

One main side effect of RK surgery is the excessive amount of time it takes for the cornea to heal (in some cases, healing takes weeks) and a structural weakening of the eye.
The following are the most common side effects and complications. Each individual may experience side effects differently. Side effects may include:

• A weakened cornea that can rupture
  
• Increased risk of infection
  
• Difficulty in fitting contact lenses, if needed
  
• Discomfort
  
• Glare and starbursts around lights
  
• Fluctuating vision during the first few months and possibly longer
  
• Cataracts (a change in the structure of the crystalline lens that causes blurred vision)
  
• Loss of vision

Benefits of RK surgery:

In most cases, RK has proven to be safe and effective for mild degrees of myopia but does not provide long-term stable vision and has therefore been replaced by the types of laser eye surgery discussed above.
 
What is astigmatic keratotomy (AK) surgery?

Astigmatic keratotomy (AK) is a surgical procedure, similar to radial keratotomy (RK), which is used to correct astigmatism (an irregularly shaped cornea which causes blurring). Instead of using a radial pattern of incisions, the  eye surgeon makes the incisions in a curved pattern when performing AK surgery.
 
What is automated lamellar keratoplasty (ALK) ?

Automated lamellar keratoplasty, or ALK, is a surgical procedure that was mainly used for hyperopia (farsightedness) and severe cases of myopia (nearsightedness). It has been replaced by LASIK due to the greater precision that can be provided when the excimer laser is used.
 
How is ALK performed?

Although each procedure varies slightly, in general, ALK surgery involves the surgeon cutting a flap across the front of the cornea with a microkeratome (surgical instrument). The flap is folded to the side and a thin slice of tissue is removed from the surface of the cornea. The removal of tissue alters the central cornea, or optical zone, changing refraction. The flap is then put back in place, where it adheres without sutures.
 
Possible side effects of ALK surgery:

The following are the most common side effects and complications. Each individual may experience side effects differently. Side effects may include:

• Astigmatism (blurring caused by an irregularly shaped cornea)
  
  
• Overcorrection or Undercorrection
  
  
• Inability to wear contact lenses after the procedure
  
  
• Loss of the corneal flap, requiring a corneal graft
  
  
• Scarring
  
  
• Infection
  
  
• Vision loss
  
  
• Glare

What is laser thermal keratoplasty (LTK)?

Laser thermal keratoplasty, or LTK, applies heat from a laser to the periphery of the cornea to shrink the collagen fibers, and reshapes the cornea. When the tissue is treated thermally, it contracts the tissue and causes the central cornea to steepen. You must be 40 or older to qualify for this procedure. In general, it has been replaced by Conductive Keratoplasty.
 
 
What is conductive keratoplasty (CK)?

Conductive keratoplasty, or CK, uses heat from low-level, radio frequency waves, rather than laser or scalpel, to shrink the collagen and change the shape of the cornea. A probe that is smaller than a strand of hair is used to apply the radio waves around the outer cornea. This creates a constrictive band that increases the curve of the cornea and improves vision in mildly farsighted patients.
 
What is an intracorneal ring (Intacs)?

Intracorneal ring, or Intacs, is a micro-thin intracorneal ring that is implanted into the cornea. Intacs produces a reshaping of the curvature of the cornea, thus improving vision. Intacs are only available in the US for low degrees of myopia.
 
How to prepare for refractive eye surgery:

Most refractive eye surgeries are performed on an outpatient basis, with most procedures lasting less than one hour in duration. In preparation for surgery, you may be asked to:

• arrange for someone to drop you off and pick you up again after surgery
• not wear your contact lenses for a period of time before surgery, to prevent corneal warpage
• not wear eye make-up for a couple of days before surgery

What to expect during surgery:

Although each procedure varies slightly, in general, refractive eye surgery involves minimal discomfort. The eye is usually numbed with eye drops prior to surgery. While in surgery, you may also stay awake during the procedure. Your eye may be kept open with an eye speculum (a spring-like device between the eyelids). Specific events that occur during surgery vary depending on the type of surgery performed.
 
Recovering from surgery:

Recovery times vary depending on the surgery, but can last anywhere from a couple of days to a couple of months. The following are some common symptoms following surgery. However, each individual may experience symptoms differently. Symptoms following surgery may include:

• Sensitivity to Light
  
• Blurry Vision
  
• Minor Discomfort
  
• Dry Eyes 

For more information:
 
http://seewithlasik.com/  

For more information about eye care services available at The Ohio State University Medical Center, visit the Department of Ophthalmology Web site or call (614) 293-8116.