Safety of Laser Eye Surgery

Prior to the advent of laser technology, ophthalmologists relied purely on mechanical means of surgically correcting myopia (nearsightedness), hyperopia (far sightedness), and astigmatism.

Automated Lamellar Keratectomy is a procedure through which an automatic apparatus called a microkeratome slices an extremely thin layer of tissue from the surface of the cornea in order to alter the refractive index of the ocular lens. In the case of nearsightedness, the surgeon thins the cornea, while to correct farsightedness, he first elevates the outermost layer and then supplements the natural thickness of the lens by inserting tissue from a donor cornea.

A modicum of success was achievable through mechanical means, but the extraordinary precision necessary to perform precise alterations and the jelly-like consistency of corneal tissue below the surface layer required the development of laser technology which has revolutionized ophthalmology since its introduction.

Modern laser techniques include Photorefractive Keratectomy (PRK), in which the surgeon alters the thickness of the cornea through “ablation,” or the removal of tissue in order to alter its refractive index. Laser-Assisted in Situ

Keratomileusis (LASIK) and recent variations thereof is the preferred method for suitable candidates, while Laser Epithelial Keratomileusis (LASEK) is the option for patients whose corneal thickness is insufficient for LASIK procedures.

Millions of patients have undergone laser eye surgery since its introduction, and the vast majority of them report profound satisfaction with their results, specifically, at being able to see well without glasses or contact lenses. (1)

Surveys of patients indicate that among the other most often cited benefits are increased confidence in personal appearance, improved ability to participate in contact sports, and simply being able to see upon waking up in the morning. The latest procedures have achieved a remarkable ability to correct vision, with upwards of ninety-percent of patients of some procedures enjoying restored vision of 20/20, with many even surpassing the 20/20 standard.(2)

Purely mechanical means have largely been replaced by laser procedures because they offer such unparalleled precision, as well as increased comfort and faster recuperation. In the hands of qualified ophthalmologists, all laser eye surgery is relatively safe, but like all surgical procedures, there are certain risks and potential complications inherent to the use of lasers in eye surgery. These can be minimized to large degree by careful patient selection and through application of procedures most appropriate to individual cases. More often than not, even those relatively rare incidents of unsatisfied patients reflect unrealistic pre-operative patient expectations, rather than technical or procedural failure. Therefore, ophthalmologists have learned to minimize patient frustrations by educating prospective patients as to the limitations and possible complications currently associated with laser eye surgery.

1. Maloney R, MD, Kraff C, MD, Colberston W, MD, O’Brien T, MD, Koch D, MD. Multicenter Trial of Wavefront-Guided LASIK ASCRS/ASOA Annual Symposium & Congress, San Francisco, April 2003.

2. Slade SG, MD, U.S. Clinical Trial of LASIK for Myopia with the Zyoptix System: Efficacy Assessment and Patient

Satisfaction ASCRS/ASOA Annual Symposium & Congress, San Francisco, April 2003.

Candidate Criteria:

significant category of post-operative complications relates to proper patient screening and procedure selection. Since many of the dangers and particular post- operative complications inherent in laser eye surgery vary directly as functions of prospective patient suitability, an outline of established criteria for patient selection is central to the analysis of possible risks and relative dangers associated with laser eye surgery.

Generally speaking, there are three main categories of prospective patients with respect to LASIK surgery. Predictably, statistics related to surgical error and post-operative complications and failures are markedly different where physicians adhere rigidly to accepted medical criteria delineating ideal patient candidates from less than ideal candidates, and where inappropriate candidates are preemptively excluded from any attempted laser surgery procedures.

Regardless of candidate criteria, there are certain risks and limitations inherent in laser eye surgery, even in the most optimistic scenarios. Therefore, it is always imperative — both ethically, as well as a practical matter — that patients be fully and completely informed that certain aspects of their vision might deteriorate as a consequence of (even) successful surgery, and that complete recuperation may take six months or more.

Ideal Prospective Patients for Laser Sugery:

Ideal prospective patients are older than eighteen years of age, because their eyes are no longer growing and changing in shape, and the problems for which they seek treatment fall within the category of pathology for which LASIK procedures are most appropriate such as myopia, hyperopia, and/or astigmatism. Within each different problem, there also exists an appropriate range of visual acuity defining ideal prospective candidates: namely, myopia no greater than minus-12 diopters, hyperoptia no greater than plus-6 diopters, and astigmatism no greater than 6 diopters.

Irrespective of age, another indication of stability concerning eye shape and size is the maintenance of the same contact lens prescription (or glasses) for at least two years.

Since the LASIK procedure employs a corneal flap technique, it is crucial that the corneal tissue thickness of a prospective patient be sufficient for the surgical creation of a flap appropriate in depth to ensure success of the procedure. Therefore, ideal candidates are those with relatively thick corneas.

Ideal candidates do not suffer from eye disease or from any other disease or autoimmune disorders that might delay or retard surgical healing or resistance from infection. Similarly, ideal candidates for laser surgery are not taking any medications that increase bleeding or edema. Finally, it is highly desirable that prospective patients fully understand the nature of their eye problems and the degree to which those issues are reversible through laser surgery, as well as the likelihood and nature of post- operative recuperative delays and residual vision problems and limitations.

Less Than Ideal Candidates:

Certain prospective laser surgery patients are suitable candidates, but not at the time of their first consultation. Included within this category are prospective patients younger than eighteen, or whose vision has not remained stabilized by virtue of any other factor, regardless of chronological age. Prospective patients should not be pregnant or nursing at the time of surgery, nor should a patient be considered who has had an active case of ocular herpes, or been diagnosed with ocular herpes within one year of laser surgery.(3)

3. Carr JD, Nardon R. Jr., Stulting RD, et al. Risk Factors for Epithelial Complications after LASIK. Invest Ophthalmol Vis Sci 1997;28(4):S232.

Additionally, the technical specifications of surgical laser equipment is still evolving, so some prospective patients whose visual acuity lies outside current acceptable parameters of available technology are not suitable candidates at the time of their initial consultation, but will be ideal candidates in the near future as physicians become able to treat more serious corneal deformities.

Prospective patients with scarred corneas are not necessarily precluded from consideration, but they represent a challenge to the skill and experience of the surgeon. Similarly, prospective patients suffering from autoimmune diseases, or taking medications that compromise their relative recuperative ability might be appropriately and safely treated, provided more stringent measures are taken with respect to monitoring their post surgical progress. The final consideration in this category are patients with a previous history of any condition such as dry eyes that is reliable predictor of post-surgical conditions about which they must be fully informed, primarily so that their expectations prior to laser surgery comport with the realities and possible limitations of the anticipated surgical outcomes.

Inappropriate Candidates:

Certain prospective patients are absolutely precluded from consideration for laser eye surgery because prior experience and statistical data have established that laser surgery is not sufficiently likely to improve their vision. In many cases, treating these patients is an ethical violation owing to the unacceptable risk of irreversible injury to their eyes.

Prospective patients suffering from glaucoma, corneal disease such as advanced cataracts, or whose corneal tissue is inherently too thin for the safe application of laser surgical techniques are absolutely precluded from consideration for laser surgery.

Since LASIK surgery can permanently effect depth perception, certain individuals will be precluded from consideration simply by virtue of their lifestyle or vocation. Military pilots represent one example of prospective patients who are not appropriate candidates for certain laser procedures, as are mountain climbers and deep-sea divers, by virtue of their need for accurate depth perception as well as their exposure to extreme variations in atmospheric pressure that could temporarily compromise their vision or even result in permanent blindness in extreme cases.

Post-Surgical Complications and Associated Risks:

Laser surgery was specifically developed in order to minimize the tissue trauma associated with eye surgery, and it is designed to allow the physician a greater degree of surgical precision than possible with a microkeratome. Nevertheless, even the most precise laser surgery still entails incisions (and excisions) of living tissue that requires time to heal properly.

Among the many issues that contribute to surgical healing, some require prudence on the part of the patient and diligence on the part of the surgeon, while others are strictly subject to the overall health and physical condition of the patient as well as genetic factors. Patients must adhere strictly to post-operative follow-up care and to other instructions issued by the physician.

As is the case with all other types of surgery, one of the most disastrous complications is infection at the site of the incision. In the case of laser eye surgery, there are two elements that render any type of infection particularly dangerous: the fact that eyesight might be damaged beyond repair by any infection that is not treated immediately, and by virtue of some of the procedures’ involving flaps of tissue that are re-secured for post operative healing. Tissue flaps always present greater infection risks than incisions, as a function of the greater surface area potentially exposed to bacteria, and because they constitute such perfect “incubation” conditions for any infectious organism introduced to the site.

The risk of infection can be minimized to approximately 0.02% by a course of oral antibiotics in conjunction with topical antibiotic drops applied pre-operatively and post-operatively to the eye. In the relatively rare case where an infection develops, it is almost always resolved by aggressive treatment, but time is of the absolute essence as any delay in seeking appropriate medical attention could have devastating consequences.

Patients must follow instructions religiously to disinfect their hands when touching or changing any surgical dressing and when applying drops to the eye.

Since infections are most likely to occur in the first 48 to 72 hours, patients must be counseled with respect to diligent care and observation for any signs of infection particularly during this time, and must understand the importance of contacting their physician immediately if necessary.(4)

Over/Under Correction:

One of the most common post surgical complications associated with LASIK surgery relates to the degree of residual refractive error, which is more common in patients with high prescriptions at the upper limits of that which is appropriately treated with available technology. Even with the precision afforded by lasers, a residual error of approximately 10% is typical, which translates to a noticeable degree of blurred vision in patients starting out with a high degree of nearsightedness or farsightedness. In patients starting out with much lower prescriptions, the same degree of residual error is not noticeable at all. The term “error” is something of a 4. Ambrosio R, Jr., Wilson SE, Complications of Laser in Situ Keratomileusis: Etiology, Prevention and Treatment. J Refract Surg. 2001;17:350-79 misnomer, since the phenomenon relates more to the biology of healing and the uncertainties arising from natural changes in post-operative corneal curvature than from anything the surgeon caused through “error.”

Ultimately, nearsighted patients may experience some loss of vision up close overcorrection), or some loss of ability to see far away (undercorrection). The exact opposite is true in patients who are initially farsighted. Either way, if the distortion is significant, it is usually addressed in a subsequent surgical enhancement performed after at least three to six months post-surgery.

Regression:

Closely related to over and undercorrection is the issue of regression, characterized by minor deterioration in vision compared to the immediate results of surgery. It is caused when the eye reverts to some degree of near or farsightedness upon healing, and like over/undercorrection, it is treated by a post-operative enhancement procedure a few months after the original surgery when present to a sufficient degree.

Diffuse Lamellar Keratitis (DLK):

DLK is statistically much more rare than correction error complications, but it occurs in approximately 1 in every 500 cases. It consists of a sterile, non-infectious inflammation underneath the corneal flap. Normally, it resolves with application of prescription of medicated eye drops, but occasionally it requires a surgical procedure whereby the underside of the flap is physical rinsed out. DLK represents another example of the importance of follow-up care, since it is usually asymptomatic and readily treatable, but can result in the loss of vision if it is not addressed in timely fashion. DLK is not apparent except through the use of a specialized instrument called a slit lamp, which is of crucial importance, since detailed statistical analysis reveals incidence of some degree of DLK in as many as one in every twenty-five

LASIK procedures, the vast majority of which resolve spontaneously without treatment. Approximately 1 in 5000 cases develops into potentially serious consequences, so all LASIK patients must be observed very carefully for this particular potential complication.

Dry Eyes:

Patients who experienced symptoms of dry eyes pre-operatively are markedly more likely to present with symptoms of dry eyes after certain laser procedures in which sensory nerve fibers involved in tear production (lacrimation) are severed.

Other suspected causes of the condition include (temporary) damage to structures called “goblet cells” which play a role in maintaining proper ocular lubrication. (5)

Symptoms vary in degree, and often resolve spontaneously after a few months, but it is for this reason that ideal prospective laser surgery patients are those who have not experienced dry eyes previously. Severe cases can result in symptoms of another set of complications, namely, glare, halos and starbursts for the duration of the dry eyes condition. Treatment for dry eyes usually consists of oral Doxycycline and specialized lubricating drops or sterile ointments.

Reduced Night Vision, Glare and Halos:

Even patients without dry eye symptoms typically experience at least mild symptoms of night vision problems and the sensation of glare or “halos” and starbursts” in the visual field. In principle, these symptoms resemble some of the experiences of (non-surgical) contact lens wearers, particularly at night, even though the mechanism of causation differs slightly. Visual quality generally declines somewhat when the pupil dilates, as it does in dimmer light. In post-operative LASIK

5. Smirennaia E, Sheludchenko V, Kourenkova N, et al. Management of Corneal EpithelialDefects Following Laser in Ssitu Keratomileusis. J Refract Surg 2001 Mar-Apr;17(2 Suppl):S196-9.

A patients, this is most often caused by temporary corneal swelling and changes in the newly forming shape of the corneal surface. Symptoms that don’t abate after initial recovery, are sometimes related to residual refractive error (over/undercorrection). In other instances, the suspected cause is decentered ablation.(6)

Decentered Ablation:

Decentered ablation is one potential complication that results from issues that can arise during surgery, rather than as a function of healing idiosyncrasies and variation in the pre-operative state of the eye. It occurs when the laser is not properly positioned, or centered, over the eye during surgery.

The main cause of decentered ablation relates to the patient’s inability to maintain proper focus during the laser surgery procedure. Depending on the degree of the patient’s failure to hold the gaze required for surgery, the physician may simply wait for the eye to realign itself before continuing, or he may employ a sophisticated instrument that is designed to immobilize the eye for the duration of the procedure.

The latest technological developments include a laser that is capable of tracking the eye automatically, but further testing is necessary, because the evidence of its ability to do so accurately enough, in practice, to eliminate decentered ablations is inconclusive.

Central Islands:

Central islands result in the center of the visual field, either when tissue is not removed completely uniformly. Another cause of central islands is thought to be related to the vaporization of corneal tissue under the laser, causing a plume that partially blocks the laser. This was much more common before the advent of the latest generation of excimer lasers.

6. Miller AE, McCulley JP, Bowman RW, Cavanaugh HD, Wang XH. Patient Satisfaction after LASIK for Myopia. CLAO J. 2001 Apr; 27(2):84-8

Epithelial Erosion:

One of the more common reported complications is epithelial erosion, which occurs as often as five to ten percent of LASIK patients. It occurs when portions of the outer layer of the epithelium (the outermost layer of the cornea) sloughs off after surgery. Epithelial erosion is different than most other potential complications in that it does not normally affect vision, and in that it does result in moderate discomfort.

Elderly patients are more prone to this complication but often it occurs for no apparent reason that can be predicted beforehand.(7) Luckily, the surface of the cornea regenerates within a few days, either on its own or with the assistance of a therapeutic soft contact lens that the surgeon may apply to protect and sooth the area while assisting tissue regrowth simultaneously.

Keratectasia:

Patients with thin corneas are particularly susceptible to losing too much tissue during laser surgery, which is precisely why scrupulous physicians devote so much effort to carefully screening them out of consideration.(8) Sometimes it occurs nevertheless, in which case there is no surgical fix, since further laser procedures would thin the cornea even further. In that event, the usual treatment consists of prescribing rigid gas permeable contact lenses to provide corrected vision.

7. Dastgheib KA, Clinch TE, Manche EE, et al. Sloughing of Corneal Epithelium and Wound Healing Complications Associated with Laser in Situ Kerato Mileusis Patients with Epithelial Basement Membrane Dystrophy. Am J. Ophthalmol 2000;130:297-303.

8. Steinart, RF, Swami, AU. Diffuse Interface Keratitis. Review of Refractive Surgery, Jan 2000: 46-52

Unscrupulous Practitioners:

As is the case whenever the FDA approves a new drug or medical device, once approval is granted, the agency does not regulate how it used by individual physicians. “Off-label” use is considered to be within the professional prerogative of the surgeon, and a tremendous variation of skill and qualifications exists, not to mention ethics and scruples.

While results vary, in general, there is no dispute that a disproportionate number of disappointing results are the result of unscrupulous practices. Laser eye surgery is a lucrative business, and the development of the technology has resulted in virtual of explosion of discount laser eye surgery centers throughout the country.

Laser eye surgery equipment and procedures are designed for specific problems such as myopia, hyperopia, astigmatism, or combinations of those specific problems. Whereas the FDA sanctions approval for particular laser equipment in terms of safety and general effectiveness for laser surgery, it does not monitor or regulate the proper application of individual lasers to particular problems. Therefore, significant factor for ensuring a successful result depends on the proper selection of lasers and procedures whose properties are appropriate to the particular problem represented by each patient after rigorous patient screening and selection.

Typically, these clinics are characterized by doing a high volume business, that is partly responsible for their ability to provide services at very competitive prices. Whereas patients who consult private practitioners usually establish a relationship with their prospective doctor over several meetings, patients at discount clinics often meet their surgeon for the first time when they are prepped for the procedure. Similarly, rather than obtaining follow-up care from their surgeon, patients at discount clinics sometimes see a different professional on every single visit. This fact alone probably increases the incidence of post-operative complications since there is no substitution for the recollections of the surgeon who performed the procedure. By the same token, the independent contractors who provide their services to discount clinics see a much higher volume of patients, and without the benefit of a series of pre-operative consultations prior to surgery.

Consequently, the single most important factor under the patient’s control when it comes to minimizing the dangers and any risks inherent in laser surgery is avoiding attractive sounding offers of discount prices on the delicate application of a sophisticated medical specialty that is still developing, both procedurally as well as technologically. (9)

9. Basic Lasik: Tips on Lasik Eye Surgery, Federal Trade Commission, in cooperation with the American Academy of Opthalmology, August 2000

Bibliography

1. Ambrosio R, Jr., Wilson SE, Complications of Laser in Situ Keratomileusis:

Etiology, Prevention and Treatment. J Refract Surg. 2001

2. Carr JD, Nardon R. Jr., Stulting RD, et al. Risk Factors for Epithelial

Complications after LASIK. Invest Ophthalmol Vis Sci 1997

3. Dastgheib KA, Clinch TE, Manche EE, et al. Sloughing of Corneal

Epithelium and Wound Healing Complications Associated with Laser in Situ Keratomileusis Patients with Epithelial Basement Membrane Dystrophy. Am J. Ophthalmol 2000

4. Basic Lasik: Tips on Lasik Eye Surgery, Federal Trade Commission, in cooperation with the American Academy of Opthalmology, August 2000

5. Maloney R, MD, Kraff C, MD, Colberston W, MD, O’Brien T, MD, Koch D, MD. Multicenter Trial of Wavefront-Guided LASIK ASCRS/ASOA Annual Symposium & Congress, San Francisco, April 2003.

6. Miller AE, McCulley JP, Bowman RW, Cavanaugh HD, Wang XH. Patient Satisfaction after LASIK for Myopia. CLAO J. April 2001

7. Smirennaia E, Sheludchenko V, Kourenkova N, et al. Management of Corneal EpithelialDefects Following Laser in Situ Keratomileusis. J Refract Surg March/April 2001

8. Slade SG, MD, U.S. Clinical Trial of LASIK for Myopia with the Zyoptix System: Efficacy Assessment and Patient Satisfaction ASCRS/ASOA Annual Symposium & Congress, San Francisco, April 2003.

9. Steinart, RF, Swami, AU. Diffuse Interface Keratitis. Review of Refractive Surgery, Jan 2000