This article provides an explanation of the LASIK surgery procedure - and the potential complications.
March 1, 2001
Reprinted with permission of the Minnesota Trial Lawyer Magazine (Winter 2001)
LASIK surgery is marketed as a painless 15 minute outpatient procedure that produces almost immediate visual improvement in the vast majority of patients. LASIK surgery is estimated to be a 3 billion dollar-a-year industry in the United States, with 750,000 or more people undergoing the surgery this year, and that number expected to double in 2001.(1) To help you to evaluate potential LASIK malpractice cases,(2) this article will introduce you to the eye's basic anatomy and function, the practice of LASIK including patient selection factors and common complications, and provide you with resources for further information.
I. Refractive surgery: improving vision by changing the cornea's shape.
Refractive surgery has been evolving since the 1970's when Radial Keratotomy (RK), was first widely performed. LASIK stands for Laser Assisted In Situ Keratomileusis. The Greek prefix "kerato" is widely used in ophthalmology to mean cornea. "Smileusis" means carving or sculpting. LASIK is a laser-assisted method of corneal sculpting.
LASIK began to be performed in the United States in 1995 after the FDA approved the excimer laser (3) (originally developed by IBM to etch computer chips) to treat human eyes. The excimer laser is an ultraviolet laser capable of vaporizing a microscopic layer of cells without producing heat or scarring. Initially, excimer laser was used on the surface of the cornea, in a procedure called photorefractive keratectomy (PRK). But PRK causes the eye to be relatively painful and slow to heal. LASIK avoids these problems by using the laser beneath a surgically created flap of cornea. LASIK was widely performed as an "off label use" (4) of the excimer laser until the FDA first approved the procedure in July, 1999.
LASIK can be used to correct nearsightedness (myopia), farsightedness (hyperopia), and astigmatism, but does not correct presbyopia (an age-related progressive loss of the ability to focus at near).(5) Most LASIK patients have myopia, and that is the focus of this article, although in 1998 the FDA approved use of the excimer laser to correct hyperopia. Outcome statistics reported in popular media sources suggest that LASIK results in 20/20 acuity in approximately 80% of patients, and that up to 98% of patients will at least see well enough after LASIK to pass a drivers test, that is, they will have 20/40 vision without glasses. But serious LASIK complications can produce double, blurred or distorted vision that cannot be corrected with glasses, and may result in a permanent and dramatic decrease in functional vision.
II. LASIK's surgical landscape: the cornea.
The cornea, the part of the eye operated on during LASIK, is the frontmost tissue of the eye. It is normally transparent and does not contain blood vessels. The cornea is only 0.5 to 1 mm. thick, and is generally thinner centrally than peripherally. The cornea provides two-thirds of the eye's image focusing ("refracting") power. The other one-third is provided by the eye's internal lens, which is not involved in LASIK.
The cornea has five layers, and two of these are very important in LASIK. The outermost layer, the epithelium, is a highly sensitive tissue about six cells thick. It acts as a barrier between the inner eye and the outside world, much as skin does for the rest of the body. It also provides a smooth surface allowing light rays to pass into the eye without being distorted. The epithelium has a basement membrane that helps it to adhere to the cornea's middle layer, the stroma. If the epithelium and/or its basement membrane are abnormal, the cornea may not heal properly, and an irregular surface and/or scarring may result.
The cornea's middle layer, the stroma, is the layer at which most of the LASIK procedure is performed. The stroma accounts for about 90% of the cornea, and is made up mostly of water and layered collagen/protein fibers. Scarring in this layer can result in loss of corneal transparency. LASIK makes the stroma thinner, and repeated laser procedures (called enhancements), may cause the stroma to become dangerously thin.
III. Refractive errors are image focusing errors.
Think of the eye as a camera. Parallel light rays enter the eye through the transparent cornea. The cornea (and the eye's internal lens) then focus the light rays in much the same manner that the lens of a camera would, by bending the light rays so that they come to a single clear focus at a specific distance. This process of bending light is called refracting. In a normal eye, the cornea focuses light at a distance that produces a single sharp image on the retina, the neurosensory tissue that is akin to the film in a camera. Light rays that are bent too little or too much do not focus at the correct distance, and a blurred image results from this refractive error. How much or little a cornea refracts light depends on the cornea's curvature. That is why refractive surgery seeks to change the refracting power of the eye by changing the cornea's curvature.
In nearsightedness (myopia), the cornea is too steeply curved, giving it too much focusing power and causing light rays to focus before they reach the retina. In myopia, the eyeball itself may also be elongated, contributing to the problem of light focusing in front of instead of on the retina. Conventional spectacle or contact lenses seek to optically decrease the focal power of the cornea, and thus correct the myopia, by placing a concave spherical lens (a "minus lens") in front of the eye. LASIK seeks to achieve the same result by removing tissue from the central cornea, flattening the cornea's overall curvature and thus reducing the cornea's focusing power. Exactly the reverse is true in farsightedness (hyperopia). Astigmatism is different from myopia and hyperopia, and it can occur concurrently with either condition.
IV. Basic LASIK or Flap & Zap
Step 1 -- the Flap:
LASIK has 3 basic steps.(6) First, the surgeon applies an instrument called a microkeratome to the anesthetized surface of the eye. The microkeratome has two parts. The bottom part is basically a guide-plate held in place against the eye by a suction ring on the underside. The top part houses a surgical blade that moves across the guide plate on a geared track. The instrument works much like a cheese slicer.
After the eye is anesthetized with eye drops, the surgeon inserts the suction ring/guide plate between the patient's opened eyelids, centers it over the cornea, and turns on the suction. The suction raises the pressure in the eye from its average normal pressure of about 14 mm Hg(7). to about 65 mm Hg. This prevents the guide plate from moving during the cut, and makes the cornea sufficiently rigid for a smooth flap cut. The guide plate also helps control the flap depth.
The surgeon then attaches the top part of the microkeratome housing the surgical blade. The surgeon activates the instrument and the head automatically moves across the cornea cutting a paper thin flap of tissue in the top one-third of the stroma. There are manual microkeratomes, but many of the instruments used today are automatic.(8) The instrument has a preset "stop" that creates a hinge of tissue, either on the side by the patient's nose or the top of the cornea, depending on the microkeratome. After the flap is created, the surgeon releases the suction, removes microkeratome, and folds the flap back exposing the underlying stroma.
Step 2 -- the Zap:
The patient is then positioned beneath the excimer laser, and laser pulses are delivered to the exposed stroma. The excimer laser vaporizes tissue at the cellular level, ¼ (0.25) of a micron of tissue with each pulse, without disturbing adjacent cells. For a frame of reference, a human hair is about 70 microns thick. The laser is preprogrammed with the patient's clinical data and computer controlled to (theoretically) remove the precise amount of tissue necessary to create the desired change in the cornea's shape. The surgeon views the excimer laser applications through an operating microscope, and is responsible for making certain that the laser remains centered in the surgical zone.
Step 3 -- Replacing the Flap:
After the laser application is complete, the surgeon replaces the corneal flap in its original position and irrigates the area of the laser ablation to remove debris. Intracorneal hydrostatic forces cause the flap to adhere to the underlying cornea by itself within several minutes without the need for stitches. The cornea begins healing almost immediately. At least partial visual improvement is often noticed almost immediately. So, what can go wrong?
V. Bad Outcomes
So far, there are no long term outcome statistics on LASIK. A survey of literature reveals reported complication rates ranging from approximately 1.5% to 5%.(9) Several studies indicate a significant drop in complication rates as surgeons gain experience.(10) Most LASIK complications that significantly impair vision do so by producing corneal irregularity and/or loss of corneal transparency. In our experience, poor patient selection and flap-related complications are significant sources of people who suffer serious, potentially permanent visual disability after LASIK that could have been prevented with proper care.
Poor patient selection
LASIK is not for everyone. People who have unstable refractions (more than ½ diopter of change in refractive error within 1 year prior to LASIK), or have systemic or ocular conditions that affect wound healing, or both, are poor LASIK candidates. It is important to note that the standard of care in LASIK is evolving, and there is disagreement among refractive surgeons about whether many of the following conditions are contraindications for LASIK in all cases or only in some cases.
Systemic contraindications include poorly controlled diabetes; connective tissue disorders such as rheumatoid arthritis and Sjogren's syndrome; and auto-immune or immunodeficiency diseases such as lupus. Women who are pregnant or nursing should not have LASIK. LASIK is also contraindicated for patients taking Accutane (used to treat acne); Cordarone; (an antiarrhythmic cardiac drug), or Imitrex (a migraine headache medication). These drugs are associated with dry eyes, corneal opacity formation, corneal inflammation and epithelial defects.(11)
The following ocular conditions also pose contraindications to LASIK: A history of herpes involving the eyes; severe dry eyes; thin corneas; eye lash or eyelid abnormalities; previous eye trauma or inflammation; cataract (because refractive error can be corrected during cataract surgery making refractive surgery unnecessary); corneal dystrophies, particularly dystrophies affecting the epithelial basement membrane; recurrent corneal erosions; glaucoma; unstable refractions; large pupil size; keratoconus (a corneal dystrophy in which the central cornea progressively thins and bulges forward forming a cone shape); and contact lens warpage (where the cornea becomes misshapen by long term contact lens wear). Some of these conditions can be seen by the surgeon at the patient's physical examination. Keratoconus and contact lens warpage may be very subtle and require sophisticated preoperative testing called corneal topography to rule out.
Corneal topography is used to confirm the refractive error to be corrected by LASIK, and to identify conditions that could contraindicate LASIK. In corneal topography, an instrument projects concentric rings of light onto the cornea, the reflection from the cornea is digitized and the data interpreted by the computer to produce a color topographical map showing different areas of corneal steepness by color. When you request medical records, remember to request corneal topography, and request color copies if possible. Especially if the theory of your case is that the patient was not a good candidate due to an unstable refraction or condition such as keratoconus, topography will be an invaluable source of information for your expert.
In the surgical misadventure category, microkeratome and other flap-related complications are a significant source of problems.(12) Common among flap-related problems are incomplete, torn, irregular, or decentered flaps. Flaps may also be too thin, too thick, or extend too far so that the flap is cut entirely off (called a free cap). These complications can result from improper microkeratome assembly or placement, inadequate suction or intraoperative loss of suction, or an incomplete microkeratome pass caused by a host of reasons including operator error and instrument malfunction.
In some cases, a surgeon may avoid causing permanent and serious injury by responding correctly to a flap complication. Depending on the complication, the standard of care appears to require the surgeon to discontinue the procedure, replace the flap, and wait minimally three months before attempting to re-operate.(13) Severe flap complications, such as perforating the cornea with a flap that is too deep, threaten loss of the eye. Severe visual impairment from vascular occlusion is also possible. The suction ring raises the pressure in the eye to a level that occludes the central retinal
artery: prolonged occlusion can permanently damage the retina.
Excimer Laser Complications
Bad outcomes related to the laser portion of the procedure can result from operator error such as data entry errors and decentration of the laser pulses. Data entry is critical because the laser portion of the surgery is computer-controlled to produce the desired correction based on clinical data. Decentration, where the laser pulses are not applied in the center of the exposed stroma, but instead off to one side or other, can occur if the physician does not carefully monitor centration. Finally, if the laser itself is not well maintained, it may deliver a dose of laser different from that required. These complications can result in poor vision and under or over-corrections.
VI. Are most bad outcomes good cases? Short answer: No.
About 80% of visual improvement after LASIK occurs within the first several days, but the last 20% may take up to 6 months. Some amount of glare, halo effect, and difficulty with night vision are expected after LASIK, and usually decrease over time. This is especially important to remember if you get calls about a recent LASIK surgery -- the ultimate visual outcome often cannot be predicted sooner than 6 months postoperatively.
LASIK can result in blurry, distorted, or double vision, loss of best corrected visual acuity (meaning that, even with eyeglasses, the person's vision cannot be improved to the level that is was preoperatively), loss of contrast sensitivity, and under- or over-corrections. These problems and others may be detailed in an informed consent document your client has signed. We have seen LASIK consents as brief as one page and as comprehensive as a fifteen page information booklet. It is important to thoroughly investigate the scope of the informed consent process in your client's case, including the surgeon's marketing materials.
LASIK damages may be hard to measure and to communicate to a jury. The standard Snellen eye chart (the "E" chart), commonly used to measure vision in the familiar "20/20" terms, tests vision under high contrast conditions. It tests only the ability to read pure black letters on a pure white background. Snellen testing cannot measure an individual's ability to see in dim light, or glare, or to distinguish between subtle shades of colors. Tests to measure contrast sensitivity, multiple images and problems with depth perception do exist, but are more complex and difficult to effectively communicate.(14)
Damages may also disappear over time. It is not uncommon for patients with poor LASIK outcomes to undergo subsequent procedures to improve vision that are successful in some cases. With each further procedure, there is likely to be a 3-6 month waiting period before the visual outcome is known. In extreme cases, the cornea may need to be transplanted, requiring another year before the outcome is known. The moral of the story: realize that you may be in for the long haul with LASIK cases.
Finally, it may be difficult to obtain a favorable expert opinion for several reasons. First, LASIK is a relatively new procedure, and LASIK surgeons disagree as to the standard of care in some situations. Second, surgeons who do not routinely perform LASIK may be reluctant to offer an opinion, and conversely, surgeons who perform a great deal of LASIK may be reluctant to speak out regarding the procedure's downside. The recent explosion in the numbers of LASIKs being performed is a result of effective marketing. Certainly surgeons who routinely perform LASIK have an interest in maintaining its positive media image.
VII Other resources
An abundance of print and electronic material is available on LASIK. LASIK technology is also changing rapidly. We suggest that you visit the following websites to learn more about the procedure and about the marketing driving its success.Food and Drug Administrationwww.fda.gov/cdrh/lasik
American Academy of Ophthalmology www.eyenet.org
American Society of Cataract & Refractive Surgery www.ascrs.org
International Society of Refractive Surgery www.isrs.org
Ask Lasik Docswww.asklasikdocs.com
Internet Ophthalmology www.ophthal.org
American Academy of Optometrywww.aaopt.org
National Library of Medicinewww.nlm.nih.gov
1. Kenneth Chang, Laser Eye Surgery's Turf War, N.Y. Times, Aug. 1, 2000 at D1; Dianna Digges, Plaintiff's Bar Trains its Sights on Laser Eye Surgery, Lawyers Weekly USA, Oct. 2, 2000 at B3.
2. Discussion of potential LASIK product liability cases is beyond the scope of this article.
3. The FDA has approved certain excimer laser models for use within specified parameters. Not all lasers in use are FDA approved. For an introductory discussion of approved lasers, and so called "black/gray box" lasers, visit www.lasikinstitute.org/technology.html.
4. "Off-label use" is the permissible use of an approved drug or instrument in a way that has not been specifically FDA sanctioned.
5. For a good working explanation of myopia, hyperopia, astigmatism, and presbyopia, see the American Academy of Ophthalmology (AAO) website at www.eyenet.org.
6. See the website at www.lasikinstitute.org or www.isrs.org for step-by-step LASIK illustrations.
7. Millimeters of mercury.
8. A laser keratome (intrastromal femtosecond (Nd:YLF) laser keratome) is yet another new technology being developed and tested. See Eyenet Magazine Online Sept/Oct 2000 issue at www.eyenet.org.
9. Neal A Sher, M.D. Refractive Surgery, Minnesota Physician, September 2000; Stulting RD, Carr JD, Thompson, KP et. al. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology 1999;106(1):13-20.
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