Retreatment of Patients After Primary Refractive Surgery
Michael Rosenberg
This chapter will review retreatment of the keratorefractive surgery patient who has symptomatic ametropia following the surgery. The management of other LASIK-related complications is covered in detail in Chapter 11.
Since the initial publication of this book, there have been significant technologic advances in laser refractive surgery. For example, use of the femtosecond laser has increased significantly. The delivery of femtosecond energy has become more efficient, resulting in reduced laser times and decreased postoperative inflammation. There has been a parallel improvement in excimer laser quality and the efficiency of beam delivery for both conventional and custom treatment. This has resulted in better patient outcomes, but perhaps more importantly, it has resulted in raising patient expectations. The promises of the “possibility” of 20/20 vision with newer lasers and laser delivery techniques are likely to be misinterpreted by unsophisticated and sophisticated patients alike as tantamount to a guarantee. The sensible preoperative approach to “underpromise” and “overdeliver” requires a logical postoperative strategy for enhancement surgery.
One of the most important factors determining patient satisfaction after refractive surgery is a realistic expectation of visual function. The patient should be made to understand that refractive surgery is a process rather than a procedure. It is the responsibility of the surgeon to communicate appropriate vision goals of primary surgery as well as retreatment. The preoperative discussion should also include an explanation of the types, frequency, and potential complications of retreatment surgery. The surgeon’s philosophy and comfort with enhancement surgery are most important factors in determining the ultimate outcome for any given patient.
Most physicians performing refractive surgery can be generally described as aggressive or conservative with regard to outcomes. Aggressive surgeons will set high postoperative
vision expectations—for example, at least a 98% probability of uncorrected acuity of 20/25 or better. To achieve these results, a relatively higher probability of retreatment must be expected. More conservative surgeons may set lower goals—for example, the ability to pass the driver’s test without restriction, or performing the majority of visual tasks without spectacles or contact lenses. Patients willing to accept the less rigorous goals can expect a lower probability of retreatment. Nevertheless, patients who preoperatively seem willing to accept the possibility of a less than ideal outcome are frequently dissatisfied after surgery. Not only do they see worse than they did preoperatively with spectacles or contact lenses, but they have night vision symptoms resulting from residual refractive error. For these reasons, it is imperative that every physician performing refractive surgery be comfortable with the concept of retreatment and be knowledgeable about the various surgical techniques available. Patients who attain the highest level of postoperative visual function will be active ambassadors for the refractive surgeon. This will increase both patient referrals and the overall success of the refractive practice. Patients who achieve less than expected results after surgery are more likely to lack enthusiasm for the procedure and will communicate that feeling to the detriment of their surgeon and the field of refractive surgery. It is hoped that this chapter will allow the reader to become more comfortable if not enthusiastic about retreatment and receive the gratification that comes from patient outcomes that are “wonderful” rather than just “okay.”
vision expectations—for example, at least a 98% probability of uncorrected acuity of 20/25 or better. To achieve these results, a relatively higher probability of retreatment must be expected. More conservative surgeons may set lower goals—for example, the ability to pass the driver’s test without restriction, or performing the majority of visual tasks without spectacles or contact lenses. Patients willing to accept the less rigorous goals can expect a lower probability of retreatment. Nevertheless, patients who preoperatively seem willing to accept the possibility of a less than ideal outcome are frequently dissatisfied after surgery. Not only do they see worse than they did preoperatively with spectacles or contact lenses, but they have night vision symptoms resulting from residual refractive error. For these reasons, it is imperative that every physician performing refractive surgery be comfortable with the concept of retreatment and be knowledgeable about the various surgical techniques available. Patients who attain the highest level of postoperative visual function will be active ambassadors for the refractive surgeon. This will increase both patient referrals and the overall success of the refractive practice. Patients who achieve less than expected results after surgery are more likely to lack enthusiasm for the procedure and will communicate that feeling to the detriment of their surgeon and the field of refractive surgery. It is hoped that this chapter will allow the reader to become more comfortable if not enthusiastic about retreatment and receive the gratification that comes from patient outcomes that are “wonderful” rather than just “okay.”
▪ Indications
The basic indication for retreatment of a patient after primary refractive surgery is patient dissatisfaction due to ametropia, with stable refractive error that can be corrected safely and reliably. The patient must have decreased vision that, when corrected with appropriate refraction, results in good visual acuity. The residual refractive error must be amenable to treatment with an approved laser protocol or by appropriate incisional surgery. The patient should be informed of the potential risks and benefits of the various available retreatment techniques, and the chosen technique should conform to the patient’s risk/benefit comfort level.
Residual myopia, hyperopia, and regular astigmatism can be corrected, assuming corneal thickness and keratometry are adequate. Patients with irregular astigmatism, inadequate residual stromal bed, or extremely steep (for hyperopic retreatment) or extremely flat corneas (for myopic treatment) are more problematic. While a post-enhancement residual stromal bed of <250 µm has been a traditional limit that could not be exceeded, many surgeons now prefer to leave at least 275 µm or even more stromal tissue untouched to reduce the long-term risk of ectasia. Most surgeons agree that one should avoid steepening the cornea to ≥50 diopters (D) or flattening the cornea to <35 D.
In some cases, the result following initial surgery may be consistent with the preoperative discussion of expectations, but the patient is still unhappy. This may occur in patients who are given soft outcome predictions. For instance, they may be told “If you have refractive surgery, you will be able to do virtually everything you need to do without glasses, including driving.” A soft end point sounds good during the consultation. However, it may not sound so good after treatment, when a patient with preoperative best-corrected visual acuity (BCVA) of 20/20 has a postoperative uncorrected visual acuity of 20/25—and night vision issues. The patient can drive without glasses, but is not comfortable. In these situations, the physician must choose one of several options: remind the patient of the preoperative discussion, convince the patient that all is fine, or proceed with retreatment. A surgeon who fails to present the option of retreatment either because of an unwillingness to do a retreatment or because of a lack of comfort with the techniques will leave the patient with the perception of a less than satisfactory result. This surgeon misses the opportunity to provide the patient with a result perceived to be excellent. The surgeon should present the patient with the option of retreatment rather than waiting for the patient to request the procedure. This will instill confidence and ultimately leave the patient with a very positive experience.
Many refractive surgeons do not believe in encouraging retreatment for a patient with <20/20 visual acuity or some other surgically induced vision abnormality unless the patient expresses discontent. While this patient may not become an ambassador for LASIK surgery, there will also be no added risk due to retreatment. In the unlikely event that a retreatment problem was to develop, a patient might wonder why the surgeon encouraged a second surgery in the absence of a complaint. As surgeons become more comfortable with designing a customized retreatment surgery for their patients, it becomes easier to recommend the additional surgery. The majority of patients do benefit from retreatment when it is properly planned and executed.
Residual refractive errors, which occur during the first 6 months after treatment, result from initial overcorrection, undercorrection, or regression. The likelihood of postoperative ametropia in the immediate postoperative period increases with the degree of correction. Regression refers to minimal or no refractive error in the immediate postoperative period, and late, slow drift in the direction of the primary refractive state. The larger the preoperative correction, the more likely is regression to occur within the first 6 months to a year. A smaller number of patients will develop ametropia years after the initial treatment. This occurs more frequently in patients with larger initial refractive error and in patients initially treated for hyperopia. This is particularly true for a hyperopic patient, in whom the surgeon elected to treat the manifest correction rather than the full amount of hyperopia revealed during cycloplegic refraction. This group of patients should be allowed to adapt to the full correction prior to the initial surgery or be educated about the likelihood that they will need retreatment likely more than a year after the initial surgery.
There are multiple reasons for immediate over- or undercorrection. Inaccurate refraction may result from surgeon or technician error, or inadequate cycloplegia. Failure to calibrate the laser properly may lead to insufficient or excessive laser energy. Overcorrections may result from dehydration of the stromal bed during the procedure, particularly when the ablation time is lengthy. This is potentiated by low humidity in the laser suite or prolonged elevation of a flap during LASIK prior to initiating treatment. Undercorrections may be related to overhydration of the cornea due to high humidity or excessive irrigation prior to initiating treatment. Many early conventional myopia treatment nomograms were geared toward a slight undercorrection. They were designed to avoid overcorrection of myopia at a time when treatment of hyperopia was not available. The advent of customized treatments and improved laser quality combined with strict control of environmental factors has obviated some of these issues.
To optimize postoperative results, it is essential for each surgeon to develop a standardized LASIK technique, and to develop an individual nomogram based on the postoperative results, the equipment being used, and the conditions in the laser suite. This requires tight control and maintenance of both temperature and humidity.
▪ Common Postoperative Vision Problems
There are certain common situations in which patients voice dissatisfaction, despite apparently good outcomes. These include the following:
Asymmetry of visual acuity
Night vision symptoms
Oblique astigmatism
Unrecognized anisometropia
Asthenopia in overcorrected pre-presbyopic patients
It should be emphasized that evaluation of the true residual refractive error should always be on the basis of a cycloplegic refraction. Whether the subsequent retreatment is based on the cycloplegic refraction or manifest refraction is the surgeon’s decision.
ASYMMETRY OF VISUAL ACUITY
A patient who has very sharp 20/20 visual acuity or better in one eye but weak 20/25 acuity in the other eye will frequently complain about the weaker eye. This is especially significant when the weak eye is the dominant
eye. A patient using binocular vision will choose to derive most visual information from input of the dominant eye and thus the overall satisfaction will be dependent on the acuity in that eye. Generally, no amount of reassurance will satisfy a patient, who is able to alternately cover each eye. This comparison will be done in perpetuity until the weaker eye is corrected. Patients may be convinced not to have retreatment of a mildly myopic nondominant eye, especially if they have early presbyopic symptoms. In the presbyopic patient, it is important to evaluate the uncorrected visual function both at distance and near, prior to retreating myopia. The patient may otherwise not appreciate the benefit of this myopic eye for intermediate or near tasks.
eye. A patient using binocular vision will choose to derive most visual information from input of the dominant eye and thus the overall satisfaction will be dependent on the acuity in that eye. Generally, no amount of reassurance will satisfy a patient, who is able to alternately cover each eye. This comparison will be done in perpetuity until the weaker eye is corrected. Patients may be convinced not to have retreatment of a mildly myopic nondominant eye, especially if they have early presbyopic symptoms. In the presbyopic patient, it is important to evaluate the uncorrected visual function both at distance and near, prior to retreating myopia. The patient may otherwise not appreciate the benefit of this myopic eye for intermediate or near tasks.
NIGHT VISION SYMPTOMS
Uncorrected refractive error is the most common cause of persistent nighttime haloes and glare. Night vision issues are one of the more significant concerns of patients contemplating refractive surgery, particularly if night driving is important to the patient’s lifestyle. Persistent complaints about night vision from a patient with good visual acuity, but a residual refractive error, should be addressed with retreatment. As an example, a patient with a visual acuity of 20/20—who has a refraction of -0.50 + 1.25 × 85° may have symptoms of star-bursting related to the residual cylinder. This may become more evident at night when the pupil is larger. Effective treatment will reduce the number of patients with night vision problems following laser vision correction.
OBLIQUE ASTIGMATISM
Patients with regular oblique corneal astigmatism frequently complain of subjective visual disturbance out of proportion to visual acuity. The accurate identification and measurement of residual oblique astigmatism requires careful cycloplegic refraction as well as corneal topography and keratometry. Patients with either “with-the-rule” or “against-therule” astigmatism will have a vertical or a horizontal border in relative focus, providing sufficient visual clues in a world that is oriented vertically and horizontally. Patients with oblique astigmatism have equal defocus of vertical and horizontal borders, creating a more generalized blur.
UNRECOGNIZED ANISOMETROPIA
Patients with anisometropia will frequently have subjective complaints despite apparently good visual acuity when tested monocularly without cycloplegia. Patients with no ametropia in the dominant eye may have residual ametropia in the nondominant eye, resulting in visual symptoms when using the eyes binocularly. Overcorrected myopes with hyperopia in one eye may read the Snellen chart quite easily until dilated, and may not show a significant refractive error on manifest refraction. A young patient with a postoperative refractive error may have postoperative hyperopia with or without astigmatism of up to +1.00 to +1.25 D and still have 20/15 visual acuity. It is incumbent on the physician to perform a cycloplegic refraction on any patient with unexplained visual complaints, regardless of the uncorrected visual acuity. It is also important to perform at least one cycloplegic examination on every patient at a time when the refractive error is likely stable, and before the patient is released from postoperative care. Symptomatic patients with unrecognized overcorrection may return several years after discharge, with reduced acuity and dissatisfaction creating a situation in which accurate explanation of the issues is awkward, and correction by retreatment is somewhat more difficult.
ASTHENOPIA IN UNCORRECTED PRE-PRESBYOPIC PATIENTS
Patients with symmetric overcorrection and hyperopia may have good acuity and vague symptoms, especially if there is some degree of persistent astigmatism. Timely cycloplegic refraction will identify these patients and permit prompt retreatment.
In summary, the measurement of good uncorrected visual acuity is not the sole factor in identifying patients who are candidates for possible retreatment. Careful consideration
of patient symptoms combined with careful refraction, with and without cycloplegia, is necessary to ensure that patients will have optimal refractive outcomes.
of patient symptoms combined with careful refraction, with and without cycloplegia, is necessary to ensure that patients will have optimal refractive outcomes.
▪ Evaluation
The most important prerequisite for retreatment is refractive stability. The stability of refraction should be determined on the basis of cycloplegic and manifest refraction to avoid undercorrection of accommodating hyperopic patients and the overcorrection of accommodating myopic patients. The surgeon should determine whether the retreatment should be based on the cycloplegic or the manifest refraction. Patients should be followed for at least 5 to 6 weeks after the primary treatment before determining the potential need for retreatment. Moderately myopic patients (up to -6.00 D) may be retreated as soon as two refractions, at least 1 month apart, are stable and as soon as 2 to 3 months after an initial uncomplicated LASIK. In patients with greater amounts of myopia, patients treated for hyperopia, those treated with photorefractive keratectomy (PRK), and patients with complications from the initial treatment (e.g., corneal abrasion), retreatment should be postponed until refractive, topographic, and anatomic corneal stability is observed. For patients with significant confounding abnormalities such as visually significant striae, keratitis, or epithelial ingrowth, appropriate treatment of the pathological condition is required before retreatment with the laser. In many cases, treatment of these problems will correct the residual refractive error.
Prior to potential retreatment, a thorough examination should include monocular uncorrected visual acuity, best spectacle- corrected visual acuity (BSCVA), manifest and cycloplegic refraction, keratometry, slit-lamp examination, central and peripheral pachymetry, corneal topography, and preferably wavefront evaluation. Table 10.1 provides a checklist that summarizes these retreatment examination tasks.
Keratometry should be done to help predict the postoperative contour after retreatment. Caution is advised if the predicted average keratometry value would be >50.00 D in a hyperopic patient or <35.00 D in a myopic patient. Remember, in order to predict postoperative keratometry, use the conversion factor of 0.7 or 0.8 multiplied by the spherical equivalent of the refraction in a myopic patient. The result is subtracted from the average keratometry value. No conversion factor is needed for the hyperopic treatment. The spherical equivalent is simply added to the average keratometry value. Corneal topography must also be used to rule out the corneal ectasia.
The slit-lamp examination is important to rule out corneal pathology that could explain reduced visual acuity, such as surface disruption, striae, interface debris, inflammation, or epithelial ingrowth. The presence of cataract could also explain a change in refractive error, night vision disturbance, or decreased acuity and should be identified before additional cornea surgery is considered.
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