What are refractive errors? 

Good vision depends on how well your cornea and lens focus light rays on the retina. Light rays must bend (refract) to focus on the retina. The retina is the light-sensitive nerve layer that lines the back of the eye. It creates impulses from the light rays that are sent through the optic nerve to the brain. 

Refractive errors are vision problems caused by a cornea that is not shaped perfectly. The cornea is the clear part at the front of the eye. It bends and focuses light waves. Refractive errors cause light from an object not to be focused on the retina. This causes a blurred image. Refractive errors can occur in otherwise healthy eyes. 

There are 4 types of refractive errors:

• Nearsightedness (myopia). Close objects appear sharp. But things in the distance are blurred. The eye is longer than normal from front to back. Or the cornea is curved too much. Images focus in front of the retina instead of on it.

• Farsightedness (hyperopia). You can see distant objects clearly. But objects up close are blurred. The eye is shorter than normal. Or the cornea is too flat. Images focus behind the retina.

• Astigmatism. Objects are blurred at any distance. The cornea, lens, or both are shaped so that images aren't focused sharply on the retina.

• Presbyopia. This is also known as aging eye. The eye loses its ability to change focus because of the natural aging process. This often occurs between ages 40 and 50. Refractive surgery can’t correct this problem. Surgery can make distance vision clearer. But it may make near vision worse.  

Types of surgery 

Types of surgery to correct refractive errors include:

• LASIK (laser in-situ keratomileusis)

• Photorefractive keratectomy (PRK)

• Radial keratotomy (RK)

• Astigmatic keratotomy (AK)

• Automated lamellar keratoplasty (ALK)

• Laser thermal keratoplasty (LTK)

• Conductive keratoplasty (CK)

• Intracorneal ring (Intacs) 

You can read more about each surgery below. 

LASIK

This is surgery to correct myopia, hyperopia, or astigmatism. The procedure reshapes the cornea with an excimer laser. LASIK has replaced many of the other refractive eye surgery methods. 

This surgery is done using a computer-controlled excimer cold laser. It also uses a tool called a microkeratome (femtosecond laser). With these tools, the surgeon cuts a flap in the center of the cornea. A thin layer of tissue is removed. This flattens the cornea. The flap is replaced without stitches. It reattaches to the cornea in minutes. 

Wavefront-guided LASIK is an advanced method for measuring optical distortions in the eye. The technology can be used to evaluate the eye before surgery. It measures how light is distorted as it passes into the eye and is reflected back. This creates an optical map of the eye and shows problem areas. The wavefront technology lets a LASIK surgeon adjust the laser beam settings for a more precise procedure. This can give sharper vision and reduce nighttime vision problems.

In most cases, recovery from LASIK surgery is fast, with discomfort. Mild pain medicine and eye drops can help common after-effects of surgery such as:

• Dry eyes during healing

• Eye discomfort in the first 24 hours after surgery

Possible complications include:

• Overcorrected or undercorrected vision

• Irregular astigmatism

• Corneal haze or glare

• Sensitivity to light

• Inability to wear contact lenses

• Loss of the corneal flap and need for a corneal graft

• Scarring

• Infection

• Blurry vision or vision loss

Photorefractive keratectomy (PRK) 

This surgery is done with the same kind of excimer laser used for LASIK. PRK is done to reshape the cornea to correct mild to moderate nearsightedness (myopia). 

The excimer laser beam reshapes the cornea by removing tiny amounts of tissue from the outer surface. The procedure uses a computer to map the eye's surface. It also calculates how much tissue to remove. This surgery generally takes a few minutes. Because the cornea surface is removed, it takes a few weeks to heal. 

The most common side effects include:

• Eye pain that may last for several weeks

• Mild corneal haze right after surgery

• Glare or halos around lights for months after surgery 

Radial keratotomy (RK)

This procedure is used to correct mild myopia. Tiny cuts (incisions) called are made in the cornea with a diamond scalpel. The cuts cause flatten the center of the cornea and change its curve. This reduces refraction. Because the cornea is cut, it takes a few weeks to heal. This surgery was very common. But it has been nearly replaced by LASIK.

Possible complications include:

• Changing vision during the first few months

• Infection

• Discomfort

• A weakened cornea that can rupture

• Trouble fitting contact lenses

• Glare around lights

• Clouding of the lens (cataract)

• Vision loss

Astigmatic keratotomy (AK)  

Astigmatic keratotomy (AK) is similar to radial keratotomy (RK). This surgery is used to correct astigmatism. Instead of making radial incisions, the eye surgeon makes cuts in the cornea in a curved pattern. 

Automated lamellar keratoplasty (ALK)  

This is used for hyperopia and severe cases of myopia. For myopia, the eye surgeon cuts a flap across the front of the cornea with a special tool (microkeratome). The flap is folded to the side. A thin slice of tissue is removed from the surface of the cornea. This flattens the central cornea and reduces refraction. The flap is then put back in place. The flap reattaches itself without stitches. 

During ALK for hyperopia, the eye surgeon makes a deeper cut into the cornea with the microkeratome to make a flap. The pressure in the eye causes the corneal surface to stretch and bulge. The bulging cornea improves the optical power. This corrects the hyperopia. The flap is then put back in place. It reattaches without stitches. 

Possible complications of ALK surgery include:

• Overcorrected or undercorrected vision

• Astigmatism

• Inability to wear contact lenses

• Loss of the corneal flap and need for a corneal graft

• Scarring

• Infection

• Vision loss

• Glare

Laser thermal keratoplasty (LTK) 

This method applies heat from a laser to the edges of the cornea. This shrinks the collagen fibers and reshapes the cornea. You must be age 40 or older to have this surgery. 

Conductive keratoplasty (CK) 

This surgery is used to correct mild to moderate hyperopia. It uses heat from low-level radio waves to shrink the collagen and change the cornea's shape. A probe smaller than a strand of hair is used to apply the radio waves around the outer cornea. This creates a tight band. The band increases the curve of the cornea and improves vision. You must be age 40 or older to have this surgery. 

Intracorneal rings (Intacs) 

These are used to treat mild myopia. They are thin rings that are implanted into the cornea. They change the curve of the cornea and improve vision. 

Getting ready for surgery 

Most refractive eye surgeries are done on an outpatient basis. This means you go home the same day and don’t stay overnight in a hospital. Most surgeries last less than 1 hour. Before surgery:

• Arrange for someone to drop you off and pick you up after surgery.

• Don’t wear your contact lenses before surgery, as advised by your surgeon. This is to prevent your contact lenses from affecting the shape of the cornea.

• Don’t wear eye makeup for 2 days before surgery. 

What to expect during and after surgery 

Refractive eye surgery involves minimal discomfort. The eye is often numbed with eye drops before surgery. You may be awake during the surgery. Your eye may be kept open with an eye speculum. This is a spring-like device that is placed between the eyelids.

After surgery, you may take pain medicine and use eye drops to ease discomfort. Your eye surgeon will give you more information. The most common after-effects of surgery include:

• Sensitivity to light

• Blurry vision

• Minor discomfort

• Dry eyes 

Recovery time from surgery varies depending on the surgery. Full recovery may take days, weeks, or months. 

Choosing a procedure 

LASIK is the most common type of refractive eye surgery. Benefits of LASIK include:

• Less pain and faster recovery

• It can correct a wide range of myopia

• It can be repeated to correct vision further

• The eye is not weakened, because only one flap is cut into the cornea

• Little or no scarring of the cornea 

But other types of surgery may be more suitable for your needs. And refractive eye surgery is not an option for everyone. Talk with your eye care provider about your type of vision problem, and if surgery may be right for you.