A 37-year-old man underwent bilateral LASIK 8 years ago with the IntraLase FS laser and Visx Star S4 IR system (both from Abbott Medical Optics). His preoperative manifest refractions were -2.75 OD and -3.00 OS (Figure 1). Postoperatively, his distance UCVA was 20/15 OU.
Late last year, the patient returned with a complaint of a gradual decrease in distance vision. His UCVA was 20/30 OU, which corrected to 20/15 with a manifest refraction of -0.75 +0.75 × 85 OD and -1.00 +0.50 × 90 OS. The patient under- went transepithelial PRK enhancements in both eyes.
Eight months postoperatively, the patient’s distance UCVA is 20/40 OU and corrects to 20/20+ with a manifest refraction of -1.25 +0.25 × 85 OD and -1.25 +0.50 × 90 OS. No corneal haze is visible in either eye (Figures 2 and 3).
How would you proceed?
—Case prepared by Stephen Coleman, MD.
CHRISTOPHER L. BLANTON, MD
The key to treating this patient lies in understanding what happened during the enhancement procedure. Before that, he had a spherical equivalent of -0.375 D OD and -0.75 D OS. Eight months after the enhancement, the spherical equivalent was -1.125 D OD and -1.00 D OS. This is a bizarre outcome; the right eye has become more myopic, and the left eye shows very little difference.
The most likely explanation is that the enhancement was done as a transepithelial PRK. This term implies an all-laser, no-touch technique in which the laser is programmed to remove a certain depth of epithelium followed by ablation of the Bowman layer and stroma. After the patient’s primary corneal refractive procedure, the typical epithelial hypertrophy undoubtedly occurred. This thickened epithelium makes it very difficult to determine the location of the Bowman layer; it is not likely to be at 50 μm, as it would be in a virgin eye. In transepithelial PRK after corneal refractive surgery, much of the laser energy is therefore absorbed by the epithelium and does not end up where it is meant to go.
A better way to treat patients such as this one is to choose a method for epithelial removal that guarantees the treatment will be performed at the correct anatomical location. One example is the use of dilute alcohol to remove the epithelium. Using this method, I would feel confident about re-treating this patient with excimer laser surface ablation.
COLMAN R. KRAFF, MD
There is limited postoperative information from after this patient’s transepithelial enhancement 8 years after LASIK. The appearance of the topography suggests an incomplete central epithelial ablation during the transepithelial PRK. This resulted in the topographic appearance of a broad central island. As a result, the patient is undercorrected.
Prior to proceeding with another enhancement, it would be important to document refractive stability. If there were no interim examinations to confirm this, then I would want to confirm stability over the next 3 to 6 months. Thereafter, I would recommend removing the epithelium manually (my personal technique of choice is to use an Amoils brush). The PRK enhancement could be done either with a Visx CustomVue ablation (Abbott Medical Optics) or as a topography-guided procedure, if the technology were available. I would administer topical mitomycin C at the completion of the treatment for 10 to 15 seconds.
LOUIS E. PROBST, MD
It is unusual for the patient to be more myopic than before the PRK enhancement that was performed only 8 months ago. Because this is an atypical response, a careful analysis of all of the potential contributors to the current myopic status needs to be undertaken.
The first step would be to obtain a firm understanding of the patient’s current refraction. A cycloplegic refraction and a wavefront assessment are in order. Assuming that the cycloplegic refraction does not demonstrate that accommodation is contributing to the current myopia and the wavefront map matches the manifest refraction, the next step would be to rule out other rare potential contributors to myopia such as increased blood sugar, nuclear sclerotic cataracts, or elevated IOP.
The topographic map obtained 8 months after the PRK enhancement demonstrates some central steepening compared with the previous topography. This finding suggests that the source of the myopic regression is corneal, and the most likely source of corneal regression is epithelial hyperplasia. This diagnosis could be confirmed by comparing the corneal thickness measurements before and after the enhancement or by measuring the epithelial thickness with optical coherence tomography.
Because I do not have the immediate postoperative PRK enhancement results, I do not know if the patient was initially fully corrected and then experienced epithelial hyperplasia or if he was, in fact, undercorrected right after the PRK procedure. This undercorrection is a potential outcome with a transepithelial PRK approach if the phototherapeutic keratectomy component of the procedure does not ablate through all of the hyperplastic epithelium.
If the investigations I have described indicated epithelial hyperplasia, the safest first step would be to try debriding the epithelium without any laser ablation and to monitor the refractive effect. If this strategy resulted in some persistent myopia, further PRK might be required, but a conservative approach should be taken to avoid overcorrection. In this situation, treating one eye at a time would be appropriate.
Section Editor Stephen Coleman, MD, is the director of Coleman Vision in Albuquerque, New Mexico. Dr. Coleman may be reached at (505) 821-8880; firstname.lastname@example.org.
Section Editor Parag A. Majmudar, MD, is an associate professor, Cornea Service, Rush University Medical Center, Chicago Cornea Consultants. .
Section Editor Karl G. Stonecipher, MD, is the director of refractive surgery at TLC in Greensboro, North Carolina..
Christopher L. Blanton, MD, is the president and CEO of Inland Eye Institute in Colton, California. Dr. Blanton may be reached at (909) 825-3425; email@example.com.
Colman R. Kraff, MD, is the director of refractive surgery for the Kraff Eye Institute in Chicago. He is a consultant to Abbott Medical Optics. Dr. Kraff may be reached at (312) 444-1111; firstname.lastname@example.org.
Louis E. Probst, MD, is the national medical director of TLC Laser Eye Centers in Chicago; Madison, Wisconsin; and Greenville, South Carolina. Dr. Probst may be reached at (708) 562-2020..