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Minnesota Health Technology Advisory Committee. Minnesota Health Technology Assessments [Internet]. St. Paul (MN): Minnesota Department of Health; 1995-2001.

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Refractive Eye Surgery for Myopia

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Refractive Eye Surgery for Myopia (Nearsightedness)

In recent years, there has been a growing interest in refractive eye surgeries, mainly laser in situ keratomileusis (LASIK), which is commonly called "laser surgery", to correct nearsightedness. Refractive errors, found in approximately 50% of the United States population, are disorders of the eye in which regarded objects, either distant, close, or both, appear blurred. This occurs because the eye is too long or too short and light rays are not properly refracted or bent through the cornea and lens onto the retina, the part of the eye that transmits images to the brain. An inherited disorder found in approximately 25% of individuals, myopia (nearsightedness) usually first appears in children between the ages of 8 and 12 years, worsens during the teenage years, and stabilizes between the ages of 20 and 40 years.

LASIK's popularity is spreading faster than any long-term studies support. Word of mouth has taken the place of studies about long-term outcomes. Results indicate that the surgery can be very successful. However, there are still many unknowns. What is known is that all refractive surgeries have an element of risk associated with them.

Information about four types of refractive surgery is contained in this report and may help individuals decide whether to have refractive eye surgery. Gathering as much information as possible, talking to informed individuals (not necessarily a neighbor or friend), and then weighing the risks and benefits will enhance the chances for making a good decision about a surgery that is irreversible.

Background

Normally, the cornea and lens refract light rays onto the retina, and the resulting image is transmitted to the brain via the optic nerve. (Figure 1) If the eye is too long or too short, light rays are not properly refracted onto the retina, and the images sent to the brain appear blurred. This is known as a refractive error and is measured in units called diopters (D). When eyeglasses or contact lenses are worn, refractive errors are corrected by the addition or subtraction of focusing power to or from the cornea and lens. Eyeglasses or contact lenses provide the refractive power needed to help the eye focus images directly on the retina.

Myopia is a refractive error in which distant objects become blurred because the eye is too long and its focusing power causes light rays to focus in front of the retina. In myopic individuals, concave prescription lenses subtract focusing power. Prescriptions are preceded by a negative sign (e.g., −2.00 D). Hyperopic (farsighted) individuals wear prescription lenses that are convex and preceded by a positive sign (e.g., +2.00 D).

Corrective lenses for astigmatic individuals are shaped to compensate for the uneven curvature of the cornea and allow light rays to focus on a single point on the retina.

Besides wearing eyeglasses or contact lenses, another method of correcting refractive errors is refractive eye surgery, which is a surgical procedure that corrects refractive errors by reshaping the eye and permanently changing its focusing power. The goal is to reduce or eliminate the refractive error, to attain emmetropia (normal vision), and to reduce or eliminate the need for eyeglasses or contact lenses. Refractive surgery accomplishes this goal by removing corneal tissue thus reshaping the cornea. The four types of refractive eye surgery are radial keratotomy (RK), photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and intra ocular lenses (IOL). Of the four, LASIK is the most popular surgery now being performed.

Radial Keratotomy (RK)

With RK surgery, the patient sits in an operative chair or lies on an operating table. The operative eye is labeled, and the opposite eye is patched to ensure that the patient maintains fixation with the operative eye. Topical anesthetics are administered, and a lid speculum or separator is placed to hold the eye open.

Guided by an operative microscope, numerous partial-thickness keratotomies (incisions) are made in a radial or spoke-like pattern in the peripheral cornea. (Figure 2) Normal intraocular pressure causes the area around the incisions to steepen, flattening out the central cornea.

RK reduces refractive errors and improves visual acuity in patients with low to moderate levels of myopia. A significant percentage of patients who have this surgery will become farsighted over time, and a substantial number will require corrective lenses or another operation to achieve better vision. Both eyes may be corrected at one time, but more often only one eye is corrected at a time. Correction of the second eye occurs after the stabilization of the first eye. Under correction, the presence of residual myopia is a condition that can occur after primary surgery and may be treated with follow-up surgery (enhancement surgery). Hyperopic over correction, another result of the primary surgery, may sometimes be managed with interrupted or purse-string sutures, or LASIK. RK is now seldom used because it's accuracy is lower than with laser techniques.

Photorefractive Keratectomy (PRK)

PRK corrects low to high levels of myopia by removing a predetermined amount of tissue from the corneal surface. This is done by using the high-energy pulses of an excimer laser beam (photoablation). The patient fixates, and a round optical zone is marked on the cornea to indicate the borders of the tissue to be removed.

A small portion of a corneal epithelium (outer covering) is removed from the surface, and a section of the corneal stroma (layered connective tissue) is lasered. (Figure 3) Healing takes place through re-epithelialization (the process of becoming covered by healthy tissues).

Two lasers were approved for manufacture and marketing by the Food and Drug Administration (FDA) in 1996 and are currently being used for PRK surgery. PRK is an effective treatment for low to moderate levels of myopia but is limited due to a high likelihood of myopic worsening glare and myopic regression, particularly in patients with higher levels of myopia. Compared with RK, there are longer times to refractive stabilization, as well as more occurrences of corneal haze, reduction in contrast sensitivity, and disturbances by glare and nighttime halos. According to the FDA, there is an approximate 5% chance of patients still needing eyeglasses all the time for distances up to 15 feet, and a 15% chance of needing eyeglasses occasionally. For approximately 5% of patients, vision is slightly worse after surgery. Of those having the surgery, 95% achieved 20/40 or better vision and 65% obtained 20/20 vision.

Laser In Situ Keratomileusis (LASIK)

LASIK surgery corrects low to high levels of myopia. It is now being used for hyperopia and astigmatism as well. It is performed with the excimer laser but differs from PRK in that photoablation is performed underneath a protective flap of corneal tissue. A microkeratome, a knife used for incising the cornea, is positioned over the operative eye, and a corneal flap (not more than one fifth of the cornea) is cut. (Figure 4) This flap, which remains attached, is elevated, and the excimer laser is used to evaporate the stromal bed, resculpturing the eye under the flap. The bed is then irrigated with saline solution, the flap replaced, and healing takes place through adhesion.

In July 1998, the FDA approved the manufacture and marketing of two additional lasers used for LASIK surgery. LASIK appears to be an effective treatment for low to very high myopia. Postoperative complications may diminish visual sharpness and myopic regression is possible, but such complications are not as common as when PRK is used. Since it is a relatively new procedure the outcome over 5 years is unknown.

Intra Ocular Lenses (IOL)

In April 1999, the FDA granted pre-market approval for ocular lense implants in adults 21 years of age or older. These implants are transparent, acrylic half-circles which are about as thick as contact lenses. A small incision is made into the periphery of the cornea and the implants are inserted. The lense flattens the eye causing the needed correction for mild nearsightedness and mild astigmatism. The lenses are considered permanent implants but may be removed if necessary, with vision returning to the pre-surgery level.

There is limited information on the procedure and the FDA review panel has expressed concerns about the potential loss of clarity in the cornea over a 30-50 year period. The FDA has requested the lens manufacturer to maintain a very close watch on patients who receive surgery, which costs $2,000 to $2,500 per eye.

Patient Selection

Patient selection varies by geographic location, clinic, physician, and type of surgery being performed. There are, however, some general guidelines that are used. Selected candidates are more than 18 years of age and have no history of an ocular surface or systemic disease, no glaucoma, normal ocular pressure, stable eyesight for 12 to 18 months, and an acceptable corneal thickness. Other considerations may include the ability or inability of the patient to comply with surgical or postoperative protocols, the patient's diabetes mellitus status, presence or absence of glaucoma, whether prior eye surgery had been performed, pregnancy or breast-feeding status, and any early signs of cataracts. A thorough discussion with the physician will help determine if an individual will meet the requirements.

Cost of the Procedures

  • The patient cost for refractive eye PRK surgery (laser) is typically between $1200 and $2000 per eye.
  • The patient cost for LASIK surgery is typically between $2000 and $2500 per eye.
  • If a location can be found that does RK surgery, the patient cost is typically between $1200 and $1600 per eye.
  • The patient cost for IOL is typically between $2000 and $2500.

These costs cover a wide variety of items. Costs may include the initial exam fees, computer mapping of the eye, pre- and postprocedure exams, physicians' fees, monitoring exams for the next year, and enhancements. Fully understanding what the cost includes is an important part of the final decision of whether to have the surgery.

Safety and Complications

RK

The complications associated with RK include fluctuating vision, a weakened cornea susceptible to rupture if hit directly, infection, difficulty in fitting contact lenses, glare or starbursts around lights, pain, cataracts, and vision loss. It has been noted that endothelial cell loss continues following surgery and can contribute to higher rates of cataract or the need for cornea transplant surgery later in life.

PRK

The most common complication of PRK is the loss of corneal transparency due to subepithelial stromal haze. This can be associated with a loss of best-corrected visual acuity. This is particularly apparent in subgroups of highly myopic patients who have to undergo a greater degree of refractive correction (e.g., > 6.00 D correction). A reduction in visual acuity associated with corneal haze and glare sensitivity is a troublesome side effect of PRK. Transient rises in intraocular pressure due to steroid medication used to treat haze are of concern in some patients, particularly those at risk of optic nerve damage. Astigmatism ablations tend to cause a stronger wound response, and more optical side effects, such as irregular astigmatism, glare, halos, arcs, and starbursts.

LASIK

Most complications related to LASIK occur during surgery and are microkeratome related, such as incomplete flap creation, de-centered or irregular flap creation, free cap creation, perforation of the lenticule, intraocular penetration, sliding cap, poor adherence to the eye, decentralization, and central islands. Postoperative complications include over- or undercorrection, myopic regression, induced irregular astigmatism, flap wrinkles, corneal haze, bacterial keratitis, corneal flaps melt, epithelial ingrowth, interface debris, night vision problems and glare, and retinal detachments. The experience of the surgeon is an important factor in the success of the procedure. Proper handling of these complications can often still result in a good visual outcome.

IOL

This procedure has only been recently approved so the long-term effectiveness and safety of the implants will not be known for some time. Of the surgeries that have been done, glare, inaccurate correction, and surgical complications have been the reasons for removing the implants.

Summary of Complications

The possible complications for each surgery are listed in the following table. Where possible, a percentage of risk is listed. However, a percentage of risk cannot be found in all the reviewed references. RK and PRK are surgeries that have been done for more years and thus have more studies and more information available. LASIK is relativity new, and there are fewer peer-reviewed articles available.

After surgery, although very uncommon, vision may become worse or loss of sight in the operated eye may occur.

Vision changes as a person grows older, and refractive eye surgery will correct for the current condition, but another evaluation will have to be done on any future eye changes.

The number and type of surgeries performed determine if future surgery is an option. Otherwise, there is a very good chance of needing eyeglasses or contact lenses in order to correct for future changes.

The experience of the surgeon plays a very large role in the overall risk of complications.

Some consent forms, besides listing the risks and complications from the surgery, also list the possible complications that can result from the use of topical anesthetics or sedatives. They include allergic reactions, discomfort, nausea and vomiting, headache, and severe allergic reactions resulting in stroke, coma, or death.

Refractive Surgery Complications

ComplicationRKPRKLASIK
Glare, arcs, starbursts, halosGlare and starbursts around light during healing and up to 1 year.Time to stabilize, glare sensitivity can be up to 3 years.
6.21% to 20%
Glare and starbursts around light during healing.
47%
Undercorrection (unintended residual nearsightedness)Corrected by enhancement surgery which can be done within a week and can be done more than once but recommend not more than twice.Corrected by enhancement surgery, which can be done as soon as one week but is typically done at 3 to 4 months. It can be repeated.
8% to 99%
Corrected by enhancement surgery, which can be done as soon as one week but is typically done at 3 to 4 months. It can be repeated.
15.2% to 36.4%
Will require corrective lenses or re-operationSubstantial number will require one or the other.
25% to 36% had worse best corrected vision.
5% chance of needing eyeglasses for up to 15 feet, 15% of needing eyeglasses occasionally.About the same as PRK.
Long-term instability (progressive hyperopia, regressive myopia, refractive wobble)Possible and may require correction by wearing eyeglasses.
45%
High levels of myopic worsening and longer time for refractive stabilization.
9.1%
High likelihood of myopic regression but re-treatment is often feasible.
6% to 14.3%
Postoperative contact lens wear problemsMay be difficult to fit contact lenses after surgery.May be difficult to fit contact lenses after surgery.
13%
May be difficult to fit contact lenses after surgery.
Epithelium tearPossible.Possible.
1.5% to 9.4%
Possible. Happens during flap creation/manipulation.
Pain (immediate postop and long-termYes, in morning and swelling for many days (10% according to PERK study),Treated with topical nonsteroidal drops, anti-inflammatory agents, and soft contact lenses (up to 3 days). Significant pain in 9.7% to 24.3% of patients.Topical broad-spectrum antibiotics, topical steroids, and artificial tears are administered. During the first day 88% to 95% and lessening over a six month period.
Tearing/excess mucous - dry eyeOccasionally, as healing takes place.Occasionally, as healing takes place.
91%
Occasionally, as healing takes place.
Flap/cap necrosis (LASIK)N/A* N/A* Possible.
4.9% to 6.2%
Epithelial ingrowthN/A* Possible.Possible.
1.5% to 5.1%
Epithelial defects and recurrent erosionPossible.
2% to 11%
Possible.
48%
Possible.
1.5%
Overcorrecting (unintended farsightedness) /accommodation masking for overcorrectionLarge percentage will become farsighted over time; correction is by interrupted or purse-string sutures.
3.9%
Less likely than with RK.Less likely than with RK. Correction is done by enhancement surgery after three to four months.
Stomal infiltrates, wound contamination, and cyst formationPossible.
1.3%
Possible.
20%
Possible.
Reduced contrast sensitivity and night visionPossible.Possible.
6.7% to 12%
Possible.
Cornea iron linesAround wound profile.Seen in 14%.No information available in articles but personal communication with a surgeon verifies occurrences.
Keratitis (infectious and sterile)Possible but rare.Possible but rare.
2%
Possible but rare.
1.6%
Induced irregular astigmatismPossible.Possible.
7.4% to 9.0%
Possible.
1.5%
Increased intraocular pressure (OP) and glaucomaMay happen if second surgery performed on second eye.Transient rises are seen in some patients and may be from prolonged therapy using topical corticosteroids.
12%
Possible during intraoperative phase leading to retinal hemorrhages and vein occlusions, rare.
Scar formationRare.Rare.
2.5% to 13.7%
Rare.
Cornea disordersWeakened cornea.
2% to 11%
No information available.No information available.
Presbyopia - distance vision (immediate postop and long-term)May require eyeglasses.May require eyeglasses.May require eyeglasses.
Anisometropia (refractive mismatch between eyes)High possibility and some suggest using a monovision approach.Possible and some suggest using a monovision approach.Possible and some eye clinics give the patient the option of using a monovision approach.
Off-center cuts and incorrect ablationsPossible.Possible.Possible.
Diurnal (daily) changes in visionApprox. 1/3 have changes morning to evening.During the healing process.During the healing process.
Retina detachments/hemorrhagesNot caused by RK unless associated with corneal perforation.Possible.Rarely.
Cornea rupturePossible.N/A*N/A*
Ptosis (drooping eye lid)Rarely and mild, may require minor surgery.Rarely.Rarely.
Cap dislocationN/A*N/A*Possible.
CataractsIncidence is higher than in other surgeries and shows up later in life.No information available.No information available.
Influences outside of surgeryEyesight damage can be caused by severe traumatic blow. Certain prescription or over-the-counter drugs may affect the results of surgery.No information available.Rubbing of the eyes and application of eye makeup can dislodge flap, requiring repositioning by surgeon.

* N/A means complication listed is not applicable for this procedure.

Conclusion

The popularity of refractive eye surgery is increasing due in part, to hearing about the success of a neighbor, friend, or relative who has had the surgery. In a number of studies, patients report high satisfaction with the surgeries. However, there are adverse effects that can result from any kind of surgery. For this reason, a close analysis of whether to have the surgery should be done by anyone considering this procedure. Individuals who are considering surgery should carefully weigh the benefits and risks before making a decision. The technology used with excimer laser surgery is undergoing rapid change and is, in some instances, still in the experimental stage. The expertise of the surgeon plays a large role in determining the overall risk of the procedure. The new techniques are promising, but further studies should be done on the long-term safety and efficacy of these techniques.

Many patients, especially the young and high myopic individuals, may not achieve the results they are looking for. Some will not achieve a complete independence from eyeglasses, and, for some, eyesight will worsen as a result of the surgery. There are no studies that provide long-term results of LASIK surgeries. The short-term results are encouraging; however, the possibilities of regression, cataract formation, and the outcomes of having future eye surgery are not known. Each potential patient should carefully research the procedure being considered.

Questions to consider when evaluating refractive eye surgery include:

  • Which surgery is best?
  • Who is the best doctor for that surgery?
  • How many surgeries has the doctor performed?
  • What is the total cost?
  • Is there health insurance coverage for the procedure and for the costs of possible complications caused by the surgery?

The most important question is the one only the patient can answer:

  • Is the success rate high enough and the failure rate small enough to risk having the surgery?

In conclusion, refractive eye surgeries for myopia are elective procedures. These irreversible procedures have different degrees of benefits and risks associated with them. Persons considering refractive eye surgery should carefully weigh the decision between continued use of eyeglasses or contact lenses versus eye surgery.

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