Enhancement surgery on a patient who underwent LASIK in 1999 restored the patient’s vision to 20/15 in the affected eye, but not without careful planning and management of a complication along the way. Here is the case study.
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A patient who underwent monovision LASIK with microkeratome-generated flaps in 1999 presented in December 2012 [Figure 1] with a decline in distance vision in the right eye over the past two years. He had resumed wearing glasses for distance, but was interested in improving his uncorrected distance vision. His PMH was significant only for NIDDM. The visual exam showed an UDVA of 20/70, OD and OS, CDVA of 20/20 OD and OS, and manifest refractions were -1.50 + 0.50 @140 OD and -1.50 sph OS with a dominant right eye. IOP was normal in both eyes. The slit lamp examination revealed small-diameter LASIK flaps OU and no cataract. The dilated fundus exam was normal in both eyes.
Initial corneal tomogram, prior to enhancement surgery, showing normal post-LASIK features and normal corneal thickness.
Corneal and refractive surgeon William J. Dupps, Jr., MD, PhD, reviewed corneal imaging results, including axial and tangential curvature maps, anterior and posterior elevation maps, and corneal thickness maps to look for any evidence that the patient’s refractive regression was due to corneal instability. He also measured the depth of the 1999 microkeratome flap in the right eye [Figure 2].
Figure 2. Thick microkeratome flap OD visualized on anterior segment spectral domain OCT.
The small diameter of the prior flap would be too narrow to take advantage of the wider ablation zones and enhanced optics of a more modern excimer laser enhancement. In addition, the thick nature of the existing LASIK flap carries greater potential for destabilizing the cornea when lifted to ablate additional tissue. For these reasons, the decision was made to avoid lifting the old flap. Although one option was to perform PRK over the flap, the patient’s diabetes was only marginally controlled and Dr. Dupps was concerned about the patient’s ability to heal a large epithelial defect. The final plan involved creation of a new larger diameter, thinner femtosecond flap to provide a wider ablation zone and to avoid deeper residual bed ablation. The new flap would intersect with the prior flap’s lateral margins, so intraoperative OCT was utilized to directly visualize the flap planes after femtosecond laser delivery before the flap was lifted. The next scan [Figure 3] illustrates breakthrough of femtosecond gas bubbles into the deeper flap interface, but intraoperative visualization allowed Dr. Dupps to maintain the flap lifting tool in the intended flap interface and successfully lift the new, shallower flap and complete the desired ablation. The next image [Figure 4] shows the post-ablation appearance after replacement of the flap and resolution of the deep gas bubbles.
At the one-week follow-up, the patient had an UCVA OD of 20/20 OD. However, the patient returned six months later reporting a gradual reduction in distance vision while driving. His UDVA was 20/60-2 OD. BCVA was 20/15 OD with a manifest refraction of + 1.00 + 1.50 @ 175, indicating a hyperopic shift and induced astigmatism. No diabetic lens changes were noted, but topography indicated focal flattening within the ablation zone [Figure 5]. Slit lamp examination revealed the finding shown in the next image [Figure 6].
Given the presence of epithelial ingrowth under the new LASIK flap [Figure 7], Dr. Dupps’ next step called for a flap lift with debridement of the epithelial cells from the residual stromal bed surface and underside of the flap. Dr. Dupps cleared the surface epithelium from a 1 mm zone bordering the lifted edges of the flap, and lifted only enough of the flap to remove the epithelial cells. One day after the procedure, UCVA OD was 20/15 and has remained at that level for two years. [Figure 8]
Femtosecond laser technology provides an opportunity to create precise, custom flap geometries for cases when lifting a prior LASIK flap is undesirable. Intraoperative OCT, a novel imaging technique in the setting of refractive surgery, allowed Dr. Dupps to confirm gas breakthrough into the old LASIK flap plane and directly visualize dissection of the appropriate flap interface. Localized epithelial ingrowth was addressed with a flap lift and epithelial debridement. Overall, this approach minimized the risk of corneal destabilization from a deep LASIK enhancement, eliminated the risk of poor surface healing after surface ablation, and allowed the surgeon to leverage the broad treatment zone of the latest laser vision correction technology. This allowed the patient to regain 20/15 vision.