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Preferences differ for LASIK enhancement procedure
Two experts debate the pros and cons of performing PRK vs. lifting the flap.
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Welcome to another edition of CEDARS/ASPENS Debates. CEDARS/ASPENS is a joint society of cornea, cataract and refractive surgery specialists, here to discuss some of the latest hot topics in ophthalmology.
Dealing with post-LASIK enhancements can be a frustrating endeavor. Enhancements can be performed by surface treatment (PRK) or by lifting the flap and repeating the LASIK. There is no consensus as to which method is best.
This month, Cathleen M. McCabe, MD, and David A. Goldman, MD, debate lifting the flap vs. performing PRK for LASIK enhancement. We hope you enjoy the discussion.
Kenneth A. Beckman, MD, FACS
OSN CEDARS/ASPENS Debates Editor
Easier postop course with flap relift
When considering a laser vision correction enhancement, I am a big believer in lifting the flap rather than surface ablation. The patient experience is better, with quicker visual rehabilitation, less discomfort, shorter prescription drop schedule, fewer postoperative visits and an easier overall postoperative course. The surgery is quick, and ablation times are typically very short when performing an enhancement. And, in my experience, the flap adheres to the bed even quicker than a primary LASIK flap.
Careful evaluation of the cornea with high magnification and illumination at the slit lamp is important before lifting the flap. Surgeons may decide against relifting if the flap is very thin, of poor quality (incomplete, buttonhole or other complication), abnormally small or decentered. If epithelial ingrowth is present, attention to removal at the time of flap lift is important. Stable epithelial ingrowth can sometimes become more aggressively active after attempted removal, so the risks and benefits of a flap lift in the setting of epithelial ingrowth must be weighed.
A surface ablation may also be the better choice if the procedure is being used to treat something in addition to the enhancement. For example, in a case of anterior basement membrane dystrophy, removing the epithelium and treating the corneal stroma with laser will improve adherence of the epithelial cells as the PRK heals. PRK would also be a better choice if microstriae are present.
Apart from the above considerations, I would prefer to lift a flap.
In my experience, only one flap was difficult to lift because it was very adherent. In these situations, you have the option of aborting the flap lift and converting to a surface ablation. I inform patients preoperatively that this is always a possibility.
I have lifted flaps more than 20 years old without incident and have found that there is no relationship between time since surgery and ease of lifting the flap. Some of the easiest to lift have been the longest since time of surgery.
Preop testing and evaluation might include a corneal pachymetry, topography and even a UBM to look at the thickness of the flap. When evaluating the cornea with a slit lamp, the higher illumination and higher magnification make it easier to identify the edge of the flap. The goal is to identify at least a few clock hours so you have an idea of the centration and the size, and to determine if the hinge is nasal or superior.
It is important to have the right tools available. Preoperatively, I use a Sinskey hook to push posteriorly at the peripheral margin of the flap edge in order to slide the tip under the flap, and then I open that flap edge 1 to 2 clock hours by sliding the Sinskey along the inside of that edge of the flap. This makes it easier to identify in the LASIK suite, so I can grab that edge with LASIK flap-lifting forceps, and at that time a clean edge can be obtained by using a capsulorrhexis-like motion to elevate the flap edge and complete the flap lift. I have a favorite flap lifter, Buratto LASIK Flap Forceps by Katena. There are others available. The key is that it would not have teeth and be thin enough to slide easily under a minimally elevated edge. It is the capsulorrhexis motion that enables a clean epithelial edge to be created, and this decreases the risk of epithelial ingrowth.
Even with this technique, it is possible to have little tags of epithelium that can slide underneath the flap edge and increase the risk of epithelial ingrowth. To minimize the risk, a dry Weck-Cel sponge (Beaver-Visitec International) is used before replacing the flap to sweep the epithelial edge away from the flap edge. This way, any small tags are folded back over the epithelium outside of the flap. The gutter is then inspected to make sure there are no little tags under the flap edge.
I use a bandage contact lens only if there is an epithelial defect or significant areas of loose epithelium.
In a case of epithelial ingrowth, at the slit lamp I take balanced salt solution on a 27- or 30-gauge cannula, wipe the tip of the cannula with an alcohol pad and slide it underneath the edge of the flap. The alcohol will loosen any epithelial ingrowth and allow it to come out as a sheet, which I then fold over the edge of the flap on the outside so there is less of a chance of it growing underneath again. For persistent epithelial ingrowth, tissue glue such as ReSure Sealant (Ocular Therapeutix) is helpful in sealing the edge of the flap after the epithelium ingrowth is removed.
In my experience, if care is taken to create a capsulorrhexis-like flap lift, and the margin is inspected carefully to remove any tags that might be under the flap, the risk of epithelial ingrowth is small.
- For more information:
- Cathleen M. McCabe, MD, can be reached at The Eye Associates, 6002 Pointe West Blvd, Bradenton, FL 34209; email: cmccabe13@hotmail.com.
Disclosure: McCabe reports no relevant financial disclosures.
PRK avoids potential relift complications
PRK for prior LASIK enhancements is superior to lift and re-treat for multiple reasons.
For one, it avoids potential complications with relifting a flap, including epithelial ingrowth and peripheral flap melt.
In addition, when relifting, you are going deeper into the corneal stroma, so there is a slightly higher chance of destabilizing the cornea or inducing corneal ectasia. When you do PRK over LASIK, in most cases, you go no deeper than the original LASIK flap, and the LASIK flap does not really contribute to the structural integrity of the cornea.
Furthermore, depending on how long ago the patient had LASIK, even with advanced technologies such as anterior segment OCT, you cannot always predict the flap thickness or residual stromal bed thickness. The microkeratome flap could be deeper or thicker than anticipated, and after your ablation, the patient could be left with a borderline amount of residual stromal bed. All of these things can be avoided with PRK over a LASIK flap.
When relifting, there is a risk of the flap architecture not being as pristine as the original procedure. I have managed referral cases in which, upon beginning to lift the flap, I have noticed an area of original flap tear that can place the patient at a higher risk of epithelial ingrowth. If there are areas of peripheral flap melting, managing epithelial ingrowth becomes more challenging.
Another argument for PRK over a LASIK flap would be to minimize postoperative dry eye. Typically, patients undergoing LASIK enhancement may be elderly or post-cataract and already have some baseline dryness. With PRK, you do not go in as deep into the corneal innervation as you would with a relift and treatment.
The biggest downside of doing a PRK over LASIK flap as opposed to relift is the time to heal. With traditional PRK techniques, it can take up to 3 months vs. a month at most with LASIK. We typically tell LASIK enhancement patients that the vision is good in a day and great in a week, and with PRK we say it is good in a week and great in a month, so there is a little delayed satisfaction.
But the argument that PRK causes more pain is not as significant in patients undergoing PRK over a LASIK flap because when patients have already undergone LASIK, the creation of that initial flap severs a lot of corneal nerves. The reality is that a PRK over a LASIK flap is not as painful as a primary PRK procedure, especially with the modern medications we use postoperatively.
One concern with doing a PRK enhancement over a prior LASIK flap is potential disruption of the LASIK flap underneath with epithelium removal. However, if you remove the epithelium by starting centrally and moving outward, the risk of violating the LASIK flap is quite low.
I may do a LASIK lift and re-treat on my own patients in the early postoperative period because I know the corneal flap thickness and depth. But when you lift a flap done by another surgeon, you are not guaranteed that that flap architecture was perfect in the first place. Furthermore, if there is even the slightest concern that the relifted flap may not heal as well, you are safer performing PRK.
- For more information:
- David A. Goldman, MD, can be reached at Goldman Eye, 3401 PGA Blvd., Suite 440, Palm Beach Gardens, FL 33410; email: drdavidgoldman@gmail.com.
Disclosure: Goldman reports no relevant financial disclosures.