What are the types of refractive errors?

The cornea is a part of the eye that helps focus light to create an image on the retina. It works in much the same way that the lens of a camera focuses light to create an image on film. The bending and focusing of light is also known as refraction. Usually the shape of the cornea and the eye are not perfect and the image on the retina is out-of-focus (blurred) or distorted. These imperfections in the focusing power of the eye are called refractive errors. 

There are three primary types of refractive errors: myopia, hyperopia and astigmatism. Persons with myopia, or nearsightedness, have more difficulty seeing distant objects as clearly as near objects.  Persons with hyperopia, or farsightedness,  have more difficulty seeing near objects as clearly as distant objects.  Astigmatism is a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye. Combinations of myopia and astigmatism or hyperopia and astigmatism are common. 

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How do you correct refractive errors?

Glasses or contact lenses are designed to compensate for the eye's imperfections. There are also several surgical procedures to correct refractive errors.

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What is refractive surgery?

Surgical procedures aimed at improving the focusing power of the eye are called refractive surgery. 

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What are the types of refractive surgery?

Radial Keratotomy or RK and Photorefractive Keratectomy or PRK are other refractive surgeries used to reshape the cornea. In RK, a very sharp knife is used to cut slits in the cornea changing its shape. PRK was the first surgical procedure developed to reshape the cornea, by sculpting, using a laser. Later, LASIK was developed. The same type of laser is used for LASIK and PRK. Often the exact same laser is used for the two types of surgery. The major difference between the two surgeries is the way that the stroma, the middle layer of the cornea, is exposed before it is vaporized with the laser. In PRK, the top layer of the cornea, called the epithelium, is scraped away to expose the stromal layer underneath. In LASIK, a flap is cut in the stromal layer and the flap is folded back.

Another type of refractive surgery is thermokeratoplasty in which heat is used to reshape the cornea. The source of the heat can be a laser, but it is a different kind of laser than is used for LASIK and PRK. Other refractive devices include corneal ring segments that are inserted into the stroma and special contact lenses that temporarily reshape the cornea (orthokeratology).

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What is LASIK?

LASIK stands for Laser Assisted In Situ Keratomileusis. In LASIK surgery, precise and controlled removal of corneal tissue by a special laser reshapes the cornea changing its focusing power.

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When is LASIK not for me?

You are probably NOT a good candidate for refractive surgery if:

• You are not a risk taker. Certain complications are unavoidable in a percentage of patients, and there are no long-term data available for current procedures.

• It will jeopardize your career. Some jobs prohibit certain refractive procedures. Be sure to check with your employer/professional society/military service before undergoing any procedure.

• Cost is an issue. Most medical insurance will not pay for refractive surgery. Although the cost is coming down, it is still significant.

• You required a change in your contact lens or glasses prescription in the past year. This is called refractive instability. Patients who are:

• In their early 20s or younger, 

• Whose hormones are fluctuating due to disease such as diabetes,

• Who are pregnant or breastfeeding, or 

• Who are taking medications such as steroids that cause fluctuations in vision, 

are more likely to have refractive instability and probably should not have a refractive procedure.

• You have a disease (e.g. lupus, rheumatoid arthritis) or are on medications that may affect wound healing. Certain conditions, such as autoimmune diseases and immunodeficiency states, and some medications, such as retinoic acid and steroids, may prevent proper healing after a procedure.

• You actively participate in contact sports. You participate in boxing, wrestling, martial arts or other activities in which blows to the face and eyes are a normal occurrence.

• You are not an adult.  Currently, no lasers are approved for LASIK on persons under the age of 18.

Contraindications

The safety and effectiveness of refractive procedures has not been determined in patients with some diseases. Do NOT have LASIK surgery if you have a history of any of the following:

• Herpes simplex or Herpes zoster (shingles) involving the eye area.

• Glaucoma, glaucoma suspect, or ocular hypertension.

• Eye diseases, such as uveitis/iritis (inflammations of the eye) and blepharitis (inflammation of the eyelids with crusting of the eyelashes). 

• Eye injuries or previous eye surgeries.

• Keratoconus

Other Risk Factors

Your doctor should screen you for the following conditions or indicators of risk:

• Large pupils. Make sure this evaluation is done in a dark room. Younger patients and patients on certain medications may be prone to having large pupils under dim lighting conditions. This can cause symptoms such as glare, halos, starbursts, and ghost images (double vision) after surgery. In some patients these symptoms may be debilitating. For example, a patient may no longer be able to drive a car at night or in certain weather conditions, such as fog.

• Thin Corneas. The cornea is the thin clear covering of the eye that is over the iris, the colored part of the eye. Most refractive procedures change the eye’s focusing power by reshaping the cornea (for example, by removing tissue).  Performing a refractive procedure on a cornea that is too thin or has too few cells lining the back surface (endothelial cells) may result in blinding complications.

• Previous refractive surgery (e.g. RK, PRK, LASIK).  Additional refractive surgery may not be recommended.  The decision to have additional refractive surgery must be made in consultation with your doctor after careful consideration of your unique situation.

• Dry Eyes

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What are the risks?

Most patients are very pleased with the results of their refractive surgery. However, like any other medical procedure, there are risks involved. That's why it is important for you to understand the limitations and possible complications of refractive surgery.

Before undergoing a refractive procedure, you should carefully weigh the risks and benefits based on your own personal value system, and try to avoid being influenced by friends that have had the procedure or doctors encouraging you to do so.

• You may be undertreated or overtreated. Only a certain percent of patients achieve 20/20 vision without glasses or contacts. You may require additional treatment, but additional treatment may not be possible. You may still need glasses or contact lenses after surgery.  If you used reading glasses before surgery, you will still need reading glasses after surgery.

• Results are generally not as good in patients with very small or very large refractive errors. Patients that require rather weak or very strong glasses or contact lens prescriptions to see well before the procedure are less likely to have 20/20 vision without glasses or contacts after the procedure.

• Results may not be lasting. The level of improved vision you experience after surgery may be temporary, especially if you are farsighted or currently need reading glasses. It is especially important for farsighted individuals to have a cycloplegic refraction (a vision exam with lenses after dilating drops) as part of the screening process. Patients whose manifest refraction (a vision exam with lenses before dilating drops) is very different from their cycloplegic refraction are more likely to have temporary results.

• Some patients lose vision. Some patients lose lines of vision on the vision chart that cannot be corrected with glasses, contact lenses, or surgery as a result of treatment. There is little known about how refractive procedures affect other aspects of vision, such as contrast sensitivity (the ability to see objects clearly against a similar background or in dim lighting conditions). Some studies suggest that patients do not see as well in situations of low contrast, such as at night or in fog, after treatment as compared to before treatment. Therefore, patients with low contrast sensitivity to begin with probably should not have a refractive procedure. It is important for you to know that not all eye centers test contrast sensitivity, and that when it is tested, it should be done in a dark room.

• Some patients may develop severe dry eye syndrome.  As a result of surgery, your eye may not be able to produce enough tears to keep the eye moist and comfortable.  This condition may be permanent.  Intensive drop therapy and the use of plugs or other procedures may be required.

Additional Risks if you are Considering the Following:

• Monovision

Monovision is one clinical technique used to deal with the correction of presbyopia, the gradual loss of the ability of the eye to change focus for close-up tasks that progresses with age. The intent of monovision is for the presbyopic patient to use one eye for distance viewing and one eye for near viewing. This practice was first applied to fit contact lens wearers and more recently to LASIK and other refractive surgeries. With contact lenses, a presbyopic patient has one eye fit with a contact lens to correct distance vision, and the other eye fit with a contact lens to correct near vision. In the same way, with LASIK, a presbyopic patient has one eye operated on to correct the distance vision, and the other operated on to correct the near vision. In other words, the goal of the surgery is for one eye to have vision worse than 20/20, the commonly referred to goal for LASIK surgical correction of distance vision. Since one eye is corrected for distance viewing and the other eye is corrected for near viewing, the two eyes no longer work together. This results in poorer quality vision and a decrease in depth perception. These effects of monovision are most noticeable in low lighting conditions and when performing tasks requiring very sharp vision. Therefore, you may need to wear glasses or contact lenses to fully correct both eyes for distance or near when performing visually demanding tasks, such as driving at night, operating dangerous equipment, or performing occupational tasks requiring very sharp close vision (e.g., reading small print for long periods of time).

Many patients cannot get used to having one eye blurred at all times. The difference between monovision with contact lenses and monovision with LASIK is that you can always take contact lenses out or have them changed (the treatment is reversible and adjustable) as opposed to LASIK, where the result of the surgery is not reversible or adjustable. Therefore, if you are considering monovision with LASIK, make sure you go through a trial period with contact lenses to see if you can tolerate monovision, before having the irreversible surgery performed on your eyes. Just before this trial period starts, find out if you pass your state's driver's license requirements with monovision, or if you need supplemental glasses to drive.

In addition, you should consider how much your presbyopia is expected to increase in the future. Ask your doctor when you should expect the results of your monovision surgery to no longer be enough for you to see near-by objects clearly without the aid of glasses or contacts, or when a second surgery might be required to further correct your near vision.

• Bilateral Simultaneous Treatment

You may choose to have LASIK surgery on both eyes at the same time or to have surgery on one eye at a time. Although the convenience of having surgery on both eyes on the same day is attractive, this practice is riskier than having two separate surgeries. The second eye may have a higher risk of developing an inflammation if surgery is done on the same day than if surgery is performed on separate days. If a malfunction of the laser or microkeratome occurs causing a complication with the first eye, the second eye is more likely to also experience the same complication if the surgery is performed on the same day rather than on separate days.

If you decide to have one eye done at a time, you and your doctor will decide how long to wait before having surgery on the other eye. If both eyes are treated at the same time or before one eye has a chance to fully heal, you and your doctor do not have the advantage of being able to see how the first eye responds to surgery before the second eye is treated.

Another disadvantage to having surgery on both eyes at the same time is that the vision in both eyes may be blurred after surgery until the initial healing process is over, rather than being able to rely on clear vision in at least one eye at all times.

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What are the complications of refractive surgery?

Even the best screened patients under the care of most skilled surgeons can experience serious complications.

• During surgery. Malfunction of a device or other error, such as cutting a flap of cornea through and through instead of making a hinge during LASIK surgery, may lead to discontinuation of the procedure or irreversible damage to the eye.

• After surgery. Some complications, such as migration of the flap, inflammation or infection, may require another procedure and/or intensive treatment with drops. Even with aggressive therapy, such complications may lead to temporary loss of vision or even irreversible blindness.

Under the care of an experienced doctor, carefully screened candidates with reasonable expectations and a clear understanding of the risks and alternatives are likely to be happy with the results of their refractive procedure.

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What should I expect before, during, and after surgery?

What to expect before, during, and after surgery will vary from doctor to doctor and patient to patient.  This section is a compilation of patient information developed by manufacturers and healthcare professionals, but cannot replace the dialogue you should have with your doctor.  Read this information carefully and with the checklist, discuss your expectations with your doctor.

Before Surgery

If you decide to go ahead with LASIK surgery, you will need an initial or baseline evaluation by your eye doctor to determine if you are a good candidate. This is what you need to know to prepare for the exam and what you should expect:

If you wear contact lenses, it is a good idea to stop wearing them before your baseline evaluation and switch to wearing your glasses full-time. Contact lenses change the shape of your cornea for up to several weeks after you have stopped using them depending on the type of contact lenses you wear. Not leaving your contact lenses out long enough for your cornea to assume its natural shape before surgery can have negative consequences. These consequences include inaccurate measurements and a poor surgical plan, resulting in poor vision after surgery. These measurements, which determine how much corneal tissue to remove, may need to be repeated at least a week after your initial evaluation and before surgery to make sure they have not changed, especially if you wear RGP or hard lenses.  If you wear:

• soft contact lenses, you should stop wearing them for 2 weeks before your initial evaluation.

• toric soft lenses or rigid gas permeable (RGP) lenses, you should stop wearing them for at least 3 weeks before your initial evaluation.

• hard lenses, you should stop wearing them for at least 4 weeks before your initial evaluation.

You should tell your doctor:

• about your past and present medical and eye conditions

• about all the medications you are taking, including over-the-counter medications and any medications you may be allergic to

Your doctor should perform a thorough eye exam and discuss:

• whether you are a good candidate

• what the risks, benefits, and alternatives of the surgery are

• what you should expect before, during, and after surgery

• what your responsibilities will be before, during, and after surgery

You should have the opportunity to ask your doctor questions during this discussion.  Give yourself plenty of time to think about the risk/benefit discussion, to review any informational literature provided by your doctor, and to have any additional questions answered by your doctor before deciding to go through with surgery and before signing the informed consent form.

You should not feel pressured by your doctor, family, friends, or anyone else to make a decision about having surgery. Carefully consider the pros and cons.

The day before surgery, you should stop using:

• creams

• lotions

• makeup

• perfumes

These products as well as debris along the eyelashes may increase the risk of infection during and after surgery. Your doctor may ask you to scrub your eyelashes for a period of time before surgery to get rid of residues and debris along the lashes.

Also before surgery, arrange for transportation to and from your surgery and your first follow-up visit. On the day of surgery, your doctor may give you some medicine to make you relax. Because this medicine impairs your ability to drive and because your vision may be blurry, even if you don't drive make sure someone can bring you home after surgery.

During Surgery

The surgery should take less than 30 minutes. You will lie on your back in a reclining chair in an exam room containing the laser system. The laser system includes a large machine with a microscope attached to it and a computer screen.

A numbing drop will be placed in your eye, the area around your eye will be cleaned, and an instrument called a lid speculum will be use to hold your eyelids open. A ring will be placed on your eye and very high pressures will be applied to create suction to the cornea. Your vision will dim while the suction ring is on and you may feel the pressure and experience some discomfort during this part of the procedure. The microkeratome, a cutting instrument, is attached to the suction ring. Your doctor will use the blade of the microkeratome to cut a flap in your cornea.

The microkeratome and the suction ring are then removed. You will be able to see, but you will experience fluctuating degrees of blurred vision during the rest of the procedure. The doctor will then lift the flap and fold it back on its hinge, and dry the exposed tissue.

The laser will be positioned over your eye and you will be asked to stare at a light. This is not the laser used to remove tissue from the cornea. This light is to help you keep your eye fixed on one spot once the laser comes on. NOTE: If you cannot stare at a fixed object for at least 60 seconds, you may not be a good candidate for this surgery.

When your eye is in the correct position, your doctor will start the laser. At this point in the surgery, you may become aware of new sounds and smells. The pulse of the laser makes a ticking sound. As the laser removes corneal tissue, some people have reported a smell similar to burning hair. A computer controls the amount of laser delivered to your eye. Before the start of surgery, your doctor will have programmed the computer to vaporize a particular amount of tissue based on the measurements taken at your initial evaluation. After the pulses of laser energy vaporize the corneal tissue, the flap is put back into position.

A shield should be placed over your eye at the end of the procedure as protection, since no stitches are used to hold the flap in place. It is important for you to wear this shield to prevent you from rubbing your eye and putting pressure on your eye while you sleep, and to protect your eye from accidentally being hit or poked until the flap has healed.

After Surgery

Immediately after the procedure, your eye may burn, itch, or feel like there is something in it. You may experience some discomfort, or in some cases, mild pain and your doctor may suggest you take a mild pain reliever. Both your eyes may tear or water. Your vision will probably be hazy or blurry. You will instinctively want to rub your eye, but don't! Rubbing your eye could dislodge the flap, requiring further treatment. In addition, you may experience sensitivity to light, glare, starbursts or haloes around lights, or the whites of your eye may look red or bloodshot. These symptoms should improve considerably within the first few days after surgery. You should plan on taking a few days off from work until these symptoms subside. You should contact your doctor immediately and not wait for your scheduled visit, if you experience severe pain, or if your vision or other symptoms get worse instead of better.

You should see your doctor within the first 24 to 48 hours after surgery and at regular intervals after that for at least the first six months. At the first postoperative visit, your doctor will remove the eye shield, test your vision, and examine your eye. Your doctor may give you one or more types of eye drops to take at home to help prevent infection and/or inflammation. You may also be advised to use artificial tears to help lubricate the eye. Do not resume wearing a contact lens in the operated eye, even if your vision is blurry.

You should wait one to three days following surgery before beginning any non-contact sports, depending on the amount of activity required, how you feel, and your doctor's instructions.

To help prevent infection, you may need to wait for up to two weeks after surgery or until your doctor advises you otherwise before using lotions, creams, or make-up around the eye. Your doctor may advise you to continue scrubbing your eyelashes for a period of time after surgery. You should also avoid swimming and using hot tubs or whirlpools for 1-2 months.

Strenuous contact sports such as boxing, football, karate, etc. should not be attempted for at least four weeks after surgery. It is important to protect your eyes from anything that might get in them and from being hit or bumped.

During the first few months after surgery, your vision may fluctuate.

• It may take up to three to six months for your vision to stabilize after surgery.

• Glare, haloes, difficulty driving at night, and other visual symptoms may also persist during this stabilization period. If further correction or enhancement is necessary, you should wait until your eye measurements are consistent for two consecutive visits at least 3 months apart before re-operation.

• It is important to realize that although distance vision may improve after re-operation, it is unlikely that other visual symptoms such as glare or haloes will improve.

• It is also important to note that no laser company has presented enough evidence for the FDA to make conclusions about the safety or effectiveness of enhancement surgery.

Contact your eye doctor immediately, if you develop any new, unusual or worsening symptoms at any point after surgery. Such symptoms could signal a problem that, if not treated early enough, may lead to a loss of vision.

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LASIK Surgery Checklist

Know what makes you a poor candidate

Career impact - does your job prohibit refractive surgery?
Cost - can you really afford this procedure?
Medical conditions - e.g., do you have an autoimmune disease or other major illness? Do you have a chronic illness that might slow or alter healing?
Eye conditions - do you have or have you ever had any problems with your eyes other than needing glasses or contacts?
Medications - do you take steroids or other drugs that might prevent healing?
Stable refraction - has your prescription changed in the last year?
High or Low refractive error - do you use glasses/contacts only some of the time? Do you need an unusually strong prescription?
Pupil size - are your pupils extra large in dim conditions?
Corneal thickness - do you have thin corneas?
 

Know all the risks and procedure limitations

Overtreatment or undertreatment - are you willing and able to have more than one surgery to get the desired result?
May still need reading glasses - do you have presbyopia?
Results may not be lasting - do you think this is the last correction you will ever need? Do you realize that long-term results are not known?
May permanently lose vision - do you know some patients may lose some vision or experience blindness?
Development of visual symptoms - do you know about glare, halos, starbursts, etc. and that night driving might be difficult?
Contrast sensitivity - do you know your vision could be significantly reduced in dim light conditions?
Bilateral treatment - do you know the additional risks of having both eyes treated at the same time?
Patient information - have you read the patient information booklet about the laser being used for your procedure?
 

Know preoperative, operative, and postoperative expectations

No contact lenses prior to evaluation and surgery - can you go for an extended period of time without wearing contact lenses?
Have a thorough exam - have you arranged not to drive or work after the exam?
Read and understand the informed consent - has your doctor given you an informed consent form to take home and answered all your questions?
No makeup before surgery - can you go 24-36 hours without makeup prior to surgery?
Arrange for transportation - can someone drive you home after surgery?
Plan to take a few days to recover - can you take time off to take it easy for a couple of days if necessary?
Expect not to see clearly for a few days - do you know you will not see clearly immediately?
Know sights, smells, sounds of surgery - has your doctor made you feel comfortable with the actual steps of the procedure?
Be prepared to take drops/medications- are you willing and able to put drops in your eyes at regular intervals?
Be prepared to wear an eye shield - do you know you need to protect the eye for a period of time after surgery to avoid injury?
Expect some pain/discomfort - do you know how much pain to expect?
Know when to seek help - do you understand what problems could occur and when to seek medical intervention?
Know when to expect your vision to stop changing - are you aware that final results could take up to months?
Make sure your refraction is stable before any further surgery - if you don't get the desired result, do you know not to have an enhancement until the prescription stops changing?

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Zyoptix : a New Frontier in Laser Eye Treatment

The very latest development in laser eye treatment from Bausch and Lomb is a system called Zyoptix, a system that takes LASIK to a new frontier. Learn more about it by linking to the Zyoptix section.

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