Managing LASIK-Induced Epithelial Ingrowth
BY WILLIAM L. MILLER, OD, PHD, FAAO
My last two columns dealt with postoperative complications following LASIK. Continuing on this topic, here I'll discuss epithelial ingrowth. Although it occurs after LASIK, this phenomenon can occur after other ocular surgeries or trauma. They all represent ways in which epithelial cells can be introduced into areas they typically don't occupy.
In the case of LASIK, the corneal epithelial cells are introduced into the flap interface either through transfer during the procedure or by migration from the flap edge. In rare cases they may also be introduced when a buttonholed flap is generated.
The incidence rate of epithelial ingrowth after LASIK varies widely between 1 percent and 60 percent, however this includes a broad range of severity. If we consider the percentage that requires surgical intervention, the number would be close to the lower end of the range.
Most epithelial cells that are transferred to the flap interface will not grow and will fade away over time. However, in some cases the cells remain viable, especially if connected to cells outside the flap margin. Reports indicate that repeated enhancement procedures, epithelial basement disease, diabetes, diffuse lamellar keratitis and poor flap edge adhesion will all increase the incidence of epithelial ingrowth (Ambrosio, 2001; Melki, 2001; Shallhorn, 2006).
Signs and Symptoms
Subjective complaints may include a decrement in visual acuity or ocular discomfort that may mimic a foreign body sensation. The former may result from pupil obscuration or irregular astigmatism induced by a nest of epithelial cells under the flap. Both will affect best-corrected visual acuity or uncorrected visual acuity. However, it may not affect vision during the day, but may hinder night vision — so remember to ask patients about their vision during nighttime activities.
Biomicroscopy will reveal small, grayish patches of putty-like areas that represent the growing epithelial cells. Close observation of the flap edge along with a careful observation in indirect or retroillumination will reveal more subtle areas that may be located away from the flap edge. It's important to follow any isolated nest of cells from their point of origin back to the flap edge to determine whether they are truly isolated or connected in a peninsula-like fashion to flap edge epithelial cells.
A surgical intervention may be warranted when visual acuity is affected. It may also be indicated if the epithelial ingrowth is more than a millimeter from the flap edge or in cases where the eye is inflamed and there is evidence of stromal necrosis, which would indicate the initiation of a stromal melt. A shift in refractive error towards hyperopia may also indicate a stromal melt.
If the cells are not causing any visual disturbances and the eye is not inflamed, monitor the cells at each regular post-op visit and ask patients to report back urgently if they notice a change in vision or if the eye becomes irritated.
Surgical intervention may include lifting and scraping the underlying stromal bed and posterior flap with a surgical blade and irrigating the region. Haw (2001) reported using ethanol in the flap interface, but this is not a widely accepted practice. Ayala (2008) advocates the use of the Nd:YAG laser. Still others (Anderson, 2003) have advocated the use of sutures or fibrin glue to secure the flap and prevent recurrent epithelial ingrowth. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #149.
Dr. Miller is the Director, Cornea and Contact Lens Service at the University of Houston College of Optometry. He is a member of the American Optometric Association and serves on its Journal Review Board. You can reach him at firstname.lastname@example.org.