In this session from Interventional Mindset, Gary Wörtz, MD, uses the case of a high myopic patient to prompt a lively discussion with colleagues Jonathan D. Solomon, MD, and Tal Raviv, MD, on exactly how to choose between a photorefractive keratectomy (PRK) and an implantable collamer lens (ICL).
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Criteria for evaluating a borderline patient
Within the refractive realm, patients who fall into the “gray” area and are borderline candidates for different procedures can present a challenge to even experienced surgeons. So, what does a surgeon do when presented with such a patient? In the words of Dr. Wörtz, “What do I do when I have a patient that I don't know what to do with? I call my friends.”
To discuss whether PRK or ICL was the best option for a particular patient, he reached out to two of the field's most experienced cataract and refractive surgeons, who also operate with an interventional mindset: Jonathan D. Solomon, MD, and Tal Raviv, MD.
PRK case study
Dr. Wörtz shared the case of a 40-year-old, high myope who presented for a laser in situ keratomileusis (LASIK) consultation.
As represented in Table 1 below, he is -9.50 -0.75 X 105 in the right eye and -9.50 -0.50 X 90 in the left eye. His pachymetry is on the average scale, with the right eye at 527μm and the left eye at 515μm.
However, as the initial workup revealed, his residual stromal bed was less than 300μm, which Dr. Wörtz deemed too thin for LASIK. Therefore, he opted to move forward instead with a PRK evaluation.
Table 1 outlines the patient’s characteristics, OD and OS.
| OD | OS | |
|---|---|---|
| Pachymetry | 527 | 515 |
| Pentacam D Value | 0.96 | 1.61 |
| Flap Thickness | 50 (PRK) | 50 (PRK) |
| Residual Stromal Bed | 350 | 341 |
| Manifest Refraction (MRX) | -9.50 -0.75 X 105 | -9.50 -0.50 X 090 |
| IBRA Refraction | -8.75 -0.56 X 105 | -8.92 -0.33 X 090 |
Table 1: Courtesy of Gary, Wörtz, MD.
To determine whether PRK was the appropriate procedure, further evaluation was completed. The patient was graded based on an ectasia checklist, as seen in Table 2 below. As there are evidence-based findings to reduce ectasia, Dr. Solomon and Dr. Raviv both agree that the use of the corneal ectasia checklist in evaluation has twofold benefits.
First, it demonstrates to the patient the rationale for choosing one procedure over another. Second, it solidifies to any third party that the surgeon considered a range of risk factors and took precautions to avoid any adverse results, which can be particularly helpful if a litigious situation arises.
Table 2 is an ectasia checklist utilized by Dr. Wörtz to assess patients and determine the most appropriate refractive procedure.
| Yes | No | Value | |
|---|---|---|---|
| HISTORY | |||
| Age <30 | X | ||
| Increase in astigmatism error | X | ||
| Eye allergies/rubbing | X | ||
| TOPOGRAPHY | |||
| Inferior steepening | X | ||
| Pellucid marginal degeneration | X | ||
| Borderline pattern | X | ||
| INDICES | |||
| Final D ≥ 1.65 | X | ||
| Steep keratometry >46.00 | X | ||
| Flat keratometry < 40.00 | X | ||
| Post-op K < 32.00 | X | ||
| Posterior float (Pentacam) >20 microns | X | ||
| Pachymetry <500 microns | X | ||
| Residual stromal bed (RSB) <300 microns | X | ||
| Percentage tissue altered (PTA) >40 | X | 34% OU |
Table 2: Courtesy of Gary, Wörtz, MD.
The history portion of the ectasia checklist takes into consideration the following factors:
- Age: Patients under 30 have less risk of presenting with ectasia, keratoconus, or pellucid marginal corneal degeneration (PMCD)
- Astigmatic error: Increase in astigmatic error
- Eye allergies/rubbing: Consistent corneal contact can increase ectasia
Other potential history questions to pose would be what side the patient typically sleeps on, whether the patient uses a continuous positive airway pressure (CPAP) machine, and if there are any other variables that could increase ectasia risk. Also, after a change in any of these behaviors, the patient could be reevaluated and remapped for potential improvements in scoring.
The topography of the patient showed a borderline pattern of inferior steepening, which was more prevalent in the left eye. The Belin/Ambrósio enhanced ectasia display revealed a final D value of >1.65 in both eyes; however, the left eye was borderline. Keratometry produced K values in the 46D (diopters) range. The percentage of tissue altered was 34%.
The value of epithelial mapping
When evaluating borderline candidates, epithelial mapping provides information that can tip the scale in the direction of PRK or ICL. After several years of using the Orbscan, Dr. Wörtz recently upgraded to the Pentacam (Oculus).
On mapping, the right eye revealed a slight inferior steepening in the 45D range with a final D value of 0.96, which posed no cause for concern. However, the left eye revealed a thinner cornea and more inferior steepening at 46D and a final D value of 1.61, almost indicative of keratoconus, especially considering the asymmetrical aspect.
Epithelial thickness mapping raised no red flags for anterior subepithelial irregularity. The static tissue and corneal lamellae subepithelium also looked normal on analysis.
The Pentacam AXL wave device, which functions as a full biometer, measured his anterior chamber depth (ACD) at 3.85mm in the right eye and 3.92 mm in the left eye, with horizontal white to white at 11.7mm and 11.6mm, respectively, making ICL a very viable option.
Factoring in refractive error
As the refractive error increases, so does the risk. Performing PRK on a patient with 2D of myopia is considered very safe. However, a refractive error of -9D would demand substantial change to the cornea and is, therefore, not ideal.
For both PRK and LASIK, Dr. Wörtz’s limit is -8D to -9D due to the probability of a negative impact on the quality of vision when flattening the cornea more than 7D. Similarly, regardless of pachymetry, Dr. Solomon rarely chooses to perform PRK on individuals with a refractive error of -6.5D to -7D, as he is also factoring in the difficulty of finding an appropriate intraocular lens (IOL) for a flattened cornea should cataract surgery be required in the future. Dr. Raviv was also in agreement.
Taking into consideration all aspects of this patient, the surgeons concurred that an ICL would be a preferable procedure over LASIK or PRK.
ICL as a solution
Perhaps the most appealing aspect of ICL is the fact that it is adjustable and reversible. Unlike with LASIK and PRK, no tissue is removed, removing the potential risk of ectasia. In addition, there are no flap or tissue healing issues. Further, patients do not tend to lose accommodation.
Looking to the future
Another component for consideration is age. In a 40-year-old patient with presbyopia looming, an ICL can buy them 20 years before lenticular changes or cataracts may occur. If a patient lives to be 100, chances are they will require at least two vision procedures. Since ICLs are reversible in nature, this can set the patient up for future success with additional surgeries when medically necessary.
Patients in the 40 to 50 age range should be made aware that ICL is essentially a bridging procedure to improve vision until advancing presbyopic and lenticular changes begin to hamper their daily visual needs. When that occurs, proper adjustments with available alternatives will be made.
Transitioning from PRK to ICL: The patient conversation
If the patient has come into the office focused on a particular procedure but is found not to be a good candidate, it is critical to explain exactly why and pivot to an alternative in an appealing way. Point out that, though noninvasive, in PRK/LASIK, tissue is removed that cannot be replaced. ICL, on the other hand, is reversible, and the lens can be removed if the individual is truly dissatisfied.
Dr. Solomon offered advice on approaching the refractive surgery conversation with patients. He suggested starting the conversation in a broad manner by having all staff involved use the term “refractive surgery” instead of referring to a specific procedure (e.g., LASIK).
For his individual interaction, he offered this simple sample script:
“We're going to change your prescription surgically, and how we choose to do that is really up to us as a surgeon. We're going to pick the mode and methodology that suit your particular eye.”
Just saying no
All three surgeons conceded that, in certain cases, the best surgery is no surgery at all. With the different determining criteria—age, corneal measurements, and refractive error—that are prone to change, there is not one right answer. Therefore, with a borderline patient whose age dictates their vision will most likely change (due to presbyopia or another factor), waiting to receive a refractive procedure may be the best option.
When Dr. Wörtz gives refractive surgery lectures to the ophthalmology residents at the University of Kentucky, he stresses that, though LASIK and PRK are computerized surgeries where the algorithm is driven by the laser, it is still ultimately the surgeon’s job to determine who is an appropriate candidate and who is not.
After “reading the tea leaves” of history, pachymetry, and topography, he must be equally confident with moving forward or simply saying “no” to a patient.
In conclusion
Adopting an interventional mindset means being willing not only to learn and utilize new procedures but also to implement new processes to evaluate challenging, “gray-area” patients.
In all instances, it demands building up confidence and conviction as a surgeon to expand your diagnostic and surgical skill set to make difficult determinations and meet patient needs, as opposed to automatically referring them to a more experienced colleague in the field.
A commitment to an interventional mindset is a commitment to career-long learning and prioritizing optimal patient care and convenience.
