Eye Facts

Refractive Surgery

People who wear glasses or contact lenses to see clearly at a distance may have surgical options that can reduce their nearsightedness, farsightedness, and/or astigmatism. This surgery allows the individual to have increased freedom, by reducing dependence on glasses or contact lenses.

Refractive surgery

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This booklet will try to answer questions regarding Excimer Laser surgery: current procedures that may be available as an approved treatment mode, or under FDA study. This information will help you gain a better understanding of these refractive surgery procedures, and enable you to make an informed decision in choosing a surgical solution.

How Eyes Work

The ability to see is an amazing process made possible by many parts of the eye working together. Light entering the eye is first bent (or “refracted”) by the cornea (the window of the eye) through the pupil (the opening in the iris) and then travels through the lens (located behind the pupil). The lens completes refraction by fine-focusing light onto the retina. In the retina, light is changed into electric impulses that are carried by way of the optic nerve to the brain where the image is interpreted as what is seen through your visual system.


The Cornea
The cornea is the “window” of the eye. It is the first structure that focuses the light, and is the main refracting structure. The cornea is made up of five layers of strong clear tissue. The first layer (epithelium) is made up of highly regenerative cells that allow for quick healing (24-48 hours) of superficial injuries. The deeper four layers add rigidity and provide a barrier against infection.

Crystalline Lens
This normally transparent structure is responsible for 1/3 of the refraction of light that enters the eye. Located just behind the pupil, it can change in shape to allow focus to change from distant to near objects. This focus change is called accommodation. As a person matures, the lens hardens which makes accommodation more difficult.

This membrane lines the inside wall of the eye. It contains photoreceptors (rods and cones) that transmit light into sight by changing light energy into electrical impulses. These messages are transferred from the retina to the brain and reinterpreted as images.

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Refractive Conditions

Myopia (nearsightedness)
When an eye is myopic it has too much focusing power. This excess focusing ability is the result of an eyeball that is too long, or a cornea that has excessive curvature creating a steep surface. When an eye has too much focusing power the image falls in front of the retina. Those with myopia see distant objects blurred. Near objects, however, can be focused clearly.

Hyperopia (farsightedness)
A hyperopic eye does not have enough focusing power. The lack of focusing ability is the result of an eyeball that is too short, or a cornea that does not have enough curvature. When an eye lacks focusing power the image falls behind the retina. For those with hyperopia, the nearer an object is, the blurrier the image gets.

Refractive Conditions - Myopia & HyperopiaMyopia                               Hyperopia

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When an eye is astigmatic, the surface of the cornea is shaped like an egg rather than a spherical ball so the eye does not have one point of focus.

Refractive Conditions - Normal Cornea & Astigmatic CorneaNormal Cornea                    Astigmatic Cornea

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Presbyopia occurs when a patient has increased difficulty in bringing near objects into focus (such as during reading.) This is a natural change as a person ages, occurring between 45-50 years. The inability to focus up close develops because the crystalline lens becomes stiff with age, so it cannot change shape easily. Remember, changes in lens shape allow changes in focus. Those who have nearsightedness, farsightedness, or astigmatism corrected with lenses or surgery can still expect to experience presbyopia as their eye ages. There are several options to correct presbyopia that you may consider: (1) Reading glasses or bifocal glasses, (2) Surgical correction of the dominant eye for distance vision, and the other eye for near point vision (monovision), (3) Bifocal contact lenses or monovision contact lens systems.

Measuring Refraction

The prescription on a patient’s eye is measured in units called diopters. Diopters represent the amount of correction needed to allow the patient to have the best distance vision. If an eye is farsighted (hyperopic), a convex or plus lens is used. In addition, combinations of lenses are used to correct astigmatism. The final result of the measurement is referred to as a refraction or refractive error.

Non-Surgical Correction

Glasses are the most common aid used to correct refractive errors. The advantages of glasses include low cost, easy maintenance, and versatility. Disadvantages, however, include change in cosmetic appearance, replacement cost of glasses, restriction of peripheral vision and interference with recreational activities. Although surgical methods of correction are becoming increasingly popular today, glasses remain a reliable source of correction for both distance and near vision.

Contact Lenses
Contact lenses have become a popular alternative to glasses. Some advantages contact lenses have over glasses include increased freedom during activities, and less detraction from appearance. Contact lenses, however, do not come without their own problems. They require regular cleaning to prevent serious infections and not everyone can tolerate a contact lens. Some eyes are too dry or sensitive, and refractive problems such as high degrees of astigmatism cannot be corrected with all contact lenses. Before considering any other refractive procedure, contact lenses should be considered.

Orthokeratology is a technique using special gas permeable contact lenses to reshape and flatten the cornea to correct myopia or nearsightedness. There are limitations to the amount of correction possible, and this is temporary unless the patient wears a retainer lens on the eye when he or she sleeps. This technique can also cause distortion of the cornea resulting in vision loss.

Who Qualifies for Refractive Surgery?

It is wise that anyone interested in refractive surgery have a full, comprehensive eye examination to determine if they are a suitable candidate or not. However, the following list of conditions can be used as a general guideline. A patient should:

  • be at least 18 years of age or older.
  • have stable vision for at least one year prior to surgery.
  • have healthy eyes, free from retinal detachment, corneal scars, and other diseases.
  • have a refractive problem within the range of effective treatment.
  • be prepared to pay the cost of surgery privately, since most health insurance organizations do not cover the cost as it is considered elective surgery.

 Refractive Surgery Options Available Today

  • Photorefractive Keratectomy (PRK)
  • Radial Keratotomy
    Due to the advantages and benefits of the excimer laser procedures, radial keratotomy is not currently being performed.
  • Excimer LASIK
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What is LASIK?

Excimer LASIK (laser in situ keratomileusis) is a surgical procedure that also uses the excimer laser to permanently reduce or eliminate myopia, hyperopia, and or astigmatism. However, in LASIK the laser energy is not aimed directly on the outer surface of the cornea. Instead, before starting the laser treatment, an instrument called a keratome is first used to create a thin corneal flap. This flap is moved out of the way, and the laser beam is aimed at the exposed cornea. After the laser treatment, the protective corneal flap is then put back in its original position. Since the treated area is covered up by the corneal flap, healing and the recovery of vision is quicker compared to PRK.

The Surgical Procedure

Excimer LASIK is done as an outpatient procedure. Anesthetic drops are placed on the eye to numb it prior to treatment. The patient lies flat on a surgical chair, and the eyelids of the eye to be treated cleaned with antiseptic swabs. Sometimes a plastic drape is used to help keep the eye sterile and to keep the eyelashes out of the surgeon’s way. The doctor or assistant also places a lid speculum in the eye to be treated, which helps the patient to keep the eye open. The surgical chair is then rotated under the microscope of the laser, so the surgery can begin.

LASIK Surgical Procedure

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First, an instrument called a suction ring is placed on the eye to make sure that the eye has enough pressure for the keratome to work properly. As the vacuum for the suction ring is turned on, the patient will hear the loud humming of the machine that creates the vacuum for the suction ring, and it will seem as if all the lights in the room have been turned out. The doctor checks the pressure in the eye, and if it is correct, the doctor places the keratome into the suction ring, and passes it across the cornea. This creates the corneal flap. The doctor turns off the vacuum, removes the suction ring and keratome, and then lifts the corneal flap out of the way. Now the laser can be aimed at the exposed surface of the cornea, to sculpt (ablate) the proper shape and depth.

After the Excimer laser treatment, the flap is replaced over the treated area. The lid speculum and drapes are carefully removed, and drops are placed on the eye to reduce discomfort and prevent infection. Because the corneal flap protects the area treated by the excimer laser, patients do not usually need a contact lens to reduce discomfort or promote healing. Also, the outer surface of the flap has not been treated, and is smooth and clear. This allows patients to have clearer vision sooner than they would have following PRK.

Complications of LASIK

Based on current studies, the risk of complications following LASIK appears to be very small. However, there are a number of possible complications and side effects that patients should be aware of prior to surgery. Some of these are as follows:

1) Flap Complications
Very rarely, the corneal flap made by the kertome might be thin, and have a hole. If so, the final surface of the cornea might be somewhat irregular, resulting in astigmatism and poor vision. If this occurs, the procedure is stopped and the flap is allowed to heal. The LASIK can then be attempted again 6-12 months later. Infrequently, the flap might not stick down tightly after surgery, or become infected. Cells from the outer surface of the cornea (epithelial cells) might grow under the flap causing the cornea to become cloudy or irregular. An extremely rare but very concerning complication occurs when the flap is cut too deeply in the cornea, causing the eye to rupture.

2) Overcorrection or Undercorrection
The amount of correction to be achieved is determined from the pretreatment evaluation and is programmed into the excimer laser computer. Due to variations in healing and corneal response, some patients may be undercorrected or overcorrected following their LASIK. They usually do well even with a small amount of undercorrection or overcorrection. If there is a large amount of undercorrection, patients may prefer glasses or contact lenses for some of the things they do on a day to day basis, but other patients may prefer to have enhancement, an additional laser treatment. Additional laser treatments are easier to perform after LASIK than after PRK.

3) Astigmatism
Astigmatism can occur due to problems with the flap or due to a patients healing. Because of astigmatism, patients might experience ghosting, slight doubling of vision, or blurring. If necessary, residual astigmatism can often be treated with more glasses, contact lenses or further refractive surgery.

4) Glares and Halos
After refractive surgery, some patients might experience glare symptoms due to light scatter or see halos around points of light. Usually these are most noticeable at nighttime (for example when looking at headlights or street lamps). This is because at night the pupil gets larger to allow more light into the eye, so the edge of the treated area of the cornea might affect the vision. Most patients do not feel that these symptoms impair them, and they tend to lessen as the eye heals.

5) Long-term Side Effects
Long-term side effects, after-effects or complications and their risks are unknown at present due to the relatively recent development of the LASIK procedure. Currently, there are no foreseeable documented problems once healing is complete.

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Excimer PRK

The Surgical Procedure
Excimer laser PRK is done as an outpatient procedure. Anesthetic drops are placed on the eye to numb it prior to treatment. The patient lies flat on a surgical chair which is rotated under the laser. The lid of the eye to be treated is cleaned with an antiseptic swab, and the other eye has a light patch placed over it to prevent the patient from seeing double during the procedure.

The patient’s surgical procedure is programmed onto a special keycard. During the treatment procedure, the laser’s computer reads the keycard and calculates the appropriate amount of laser pulses to sculpt the cornea for each individual patient. A pre-treatment to the patient’s operative eye is performed by the laser to remove 90% of the cornea’s epithelium (the first layer of the cornea). Pre-treatment also allows the patient to adapt to the different noises and sensations produced by the laser. After pre-treatment, the doctor takes a blunt spatula and gently removes the remaining epithelial cells to prepare the surface for the refractive treatment.

Excimer PRKThe white dashed line indicates the area of the cornea that receives laser treatment.
The arrows represent Excimer laser pulses to the cornea.

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  1. Flattening of the eye or correcting nearsightedness is achieved by removing more tissue from the center of the cornea than the outer region.
  2. Flattening only along one axis corrects the astigmatism.
  3. Removing more tissue from its outer region than the center corrects for farsightedness.
Excimer PRK

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  1. Nearsightedness- Corrected by treating the central region of the cornea.
  2. Astigmatism – Corrected by treating only one axis of the cornea.
  3. Farsightedness- Corrected by treating the outer region of the cornea.

The sculpting usually lasts between 30-60 seconds (however, the total time in the operating room is approximately 20 minutes). The sculpting is computer controlled by a shutter that opens and closes to control the power of the laser’s beam.

Once the treatment is completed, anti-inflammatory and antibiotics drops are applied to the treated eye to promote healing and prevent pain and infection. A bandage soft contact lens is placed on the eye which acts as a patch to allow the surface cells to heal. The contact lens will stay in the eye for a period of 3-5 days (until the epithelium surface healing is complete). Patients may experience no discomfort, or have mild burning or pain, foreign body sensation, itchiness, light sensitivity, swelling of the lids, and/or blurring of varying degrees during the first week.

Vision will be poor until the corneal surface has re-smoothed itself. Then gradually, from one week to 6 months, it improves slowly toward the predictable changes.

Complications of Excimer Laser PRK

Based on available data, there appear to be minimal risks associated with Excimer laser surgery on the cornea. However, the are a number of side effects that patients should be aware of prior to surgery. Some of these are as follows:

1. Delayed Epithelial Healing
The outer layer of the cornea (epithelium) is removed during Excimer laser surgery. Normally, this layer replaces itself within 2-3 days. Although rare, this sometimes does not occur within the regular time period and special medications or treatments may be needed to promote healing.

2. Light Sensitivity
Most eyes are sensitive to light after the surgery. This is due to the disturbance of the eye’s tissue. Sunglasses should be worn in bright sunlight from a few days to a few weeks after surgery.

3. Corneal Haze
Sometimes during postoperative healing, different degrees of haze may develop in the cornea. Corneal haze occurs most frequently in eyes that require a large amount of correction. Most patients, however, with the exception of very severe cases are not aware of any corneal haze. If superficial corneal haze occurs, it may cause glare at night from bright lights, which may or may not interfere significantly with vision. Corneal haze usually diminishes and disappears within 6-9 months, but may not disappear in all cases. Techniques which reduce the amount of haze, and length of time that it persists are improving.

4. Initial Overcorrection
The initial treatment goal is overcorrection because the cornea tends to regress to its original shape as it heals. The eye stabilizes to near predicted results within 3 months. However, rare cases may remain overcorrected.

5. Undercorrection
Undercorrection is a more common complication than overcorrection, and is based on each individual’s rate of healing. Small amounts of undercorrection do not seriously affect the resulting vision. Large amounts however, may require further surgery of corrective lenses full or part-time for clearer vision. Repeat laser procedures can be done after six months (under the current FDA guidelines) if undercorrection remains a problem.

6. Astigmatism
Residual astigmatism can occur based on each individual’s surface healing. Some patients’ surface healing may end up irregular, leaving a small amount of astigmatism. Patients can experience ghosting, slight doubling of images, or blurring. With the use of glasses, contact lenses, or further refractive treatment, the residual astigmatism may be corrected.

7. Glare and Halos
After refractive surgery, some patients might experience glare symptoms due to light scatter or see halos around points of light. Usually these are most noticeable at night time (for example, when looking at headlights or street lamps). This is because at night the pupil gets larger to allow more light into the eye, so the edge of the treated area of the cornea might affect the vision. Most patients do not feel that these symptoms impair them, and they tend to lessen as the eye heals.

8. Long-Term Side Effects
Long-term side effects, after-effects or complications and their risks are unknown at present due to the relatively recent development of the laser procedure. Currently, there are no foreseeable, documented problems once healing is complete.

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The Benefits of Refractive Surgery

Refractive surgery has a tremendous impact on people’s lives. Benefits are apparent in many ways.

Some refractive problems cannot be corrected with conventional glasses or contact lenses. In other cases, corrective lenses can be worn but with extreme difficulty. For these people, refractive surgery provides a way to clear vision without battling with visual aids.

There are a number of jobs such as flying, firefighting, and police department work that require workers to obtain a high standard of visual acuity without visual aids. Refractive surgery is certainly a solution that would allow such people freedom to pursue the career of their choice without otherwise being restricted by their vision. It is important to understand that individual professional organizations have their own policies on refractive surgery. Anyone who is considering corrective surgery should consult with their potential employer(s) before making a decision. This ensures that surgical correction and intervention is acceptable.

With little or no dependence on glasses or contact lenses, most sports activities are greatly enhanced. No longer does one have to battle with glasses under ski goggles, losing a contact lens while swimming, or spectacles slipping down during a tennis match. Many even find their central and peripheral vision improves, and participation in sports previously found not to be feasible becomes possible.

Many people feel that glasses distract from their physical appearance. Refractive surgery is certainly a solution to this problem. However, this surgery is generally not encouraged for purely cosmetic reasons.

Many people feel handicapped by the restrictions their visual aids set. Some fear the incapacity they would experience if they ever lost their lenses, especially during an emergency. Others feel a low self-esteem because reliance on visual aids make them feel clumsy, unattractive, or left out of some activities. By reducing or eliminating dependence on visual aids for clear vision, many psychological fears may subside.

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Making Your Decision About Refractive Surgery

Refractive eye surgery is an elective procedure. Insurance companies state it is not a requirement for health or survival. Corrective surgery is a benefit due to modern technology and medicine that can enhance the quality of life. Every type of surgery has its risks, and elective surgeries have additional costs. For you, do the benefits outweigh the risks and costs?

The answer depends as much on your personality, type of occupation, and need, as it does on the results of the surgery.

Since the ultimate decision about proceeding with surgery is yours, the following checklist has been prepared to help you decide whether or not you are the type of person who will most likely be happy with the results of refractive surgery.

You are probably not a good candidate for refractive surgery if one or more of the following statements are true for you:

  • I like wearing glasses and would feel undressed without them
  • I have no problem wearing contact lenses, and they give me excellent vision for all activities
  • My work and/or hobbies require me to consistently pay close attention to fine visual details.
  • I am the type of person who does not adapt well to change.
  • I get stressed easily if things don’t happen just the way I plan or expect.
  • I am a perfectionist.
  • I would be very disappointed if I did not end up with perfect vision after my surgery, and would consider the whole experience a failure.
  • If I still needed some correction after surgery and found out that I could not wear contact lenses as easily as before, I would be devastated.
  • I am accustomed to always having excellent vision with my corrective lenses and never regretted wearing them.
  • You will most likely be happy with the surgical experience and the results of the surgery if most of the following statements seem true to you:
  • I feel handicapped by my dependence on corrective lenses to see well
  • I have not been a very successful contact lens wearer.
  • I am a very active person who would like the freedom to participate in sports or other activities.
  • I think I look better without my glasses.
  • I sometimes fear being incapacitated if I should ever lose my corrective lenses and not be able to function in a crisis situation.
  • Having fair vision without the need of corrective lenses is more important than having perfect vision with corrective lenses.
  • I would be happy if my vision was significantly enhanced, even if I still needed to wear corrective lenses part or full time.
  • I generally adapt well to change.
  • I am a pretty easy-going person, and I do not get stressed very often.
  • I like things to be in order, but I am not a fanatical perfectionist.
  • It is important for me to see well for my work and hobbies, but I do not consistently need to focus on distant objects.
  • I would have better career opportunities if I had better natural vision.

  • I have always envied people who do not need to wear glasses or contact lenses.
  • I am financially stable and am able to pay for the surgery.

If you are interested in refractive surgery and think you might be a good candidate, please arrange a consultation with the University of Illinois at Chicago for a full evaluation and discussion.

If you are wearing contact lenses currently, the lenses need to be left off the eyes a minimum of two weeks prior to the initial exam.

 “Eye Facts” is an informational series and should not be used as a substitute for medical advice. For eye appointments, call (312) 996-6591. All Eye Facts illustrations and images are copyright protected and are the property of the UIC Board of Trustees. Unauthorized use of the images is prohibited. For usage of any Eye Facts content or illustrations please contact the Office of Medical Illustration at eyeweb@uic.edu or 312-996-5309 for licensing.
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