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What Is Epithelial Ingrowth?

Epithelial Ingrowth is a post-operative complication of LASIK surgery where cells from the outer layer of the cornea (the epithelium) migrate and grow underneath the corneal flap. Normally, the epithelium acts as a protective skin on the outside of the eye. However, if these rapidly dividing cells find a gap in the edge of the LASIK flap, they can slide into the interface, the potential space between the flap and the underlying stromal bed. Once inside, they continue to multiply, creating nests or sheets of tissue that do not belong there. While rare in primary LASIK procedures (occurring in less than 1% of cases), it is significantly more common in "enhancement" surgeries where an old flap is lifted for a touch-up.

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What Is Epithelial Ingrowth?

Epithelial Ingrowth is a post-operative complication of LASIK surgery where cells from the outer layer of the cornea (the epithelium) migrate and grow underneath the corneal flap. Normally, the epithelium acts as a protective skin on the outside of the eye. However, if these rapidly dividing cells find a gap in the edge of the LASIK flap, they can slide into the interface, the potential space between the flap and the underlying stromal bed. Once inside, they continue to multiply, creating nests or sheets of tissue that do not belong there. While rare in primary LASIK procedures (occurring in less than 1% of cases), it is significantly more common in "enhancement" surgeries where an old flap is lifted for a touch-up.

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Appearance: The Map-Like Opacity

To an eye doctor looking through a slit-lamp microscope, epithelial ingrowth has a distinct appearance. It often looks like faint white or grey islands, pearls, or map-like lines extending from the edge of the flap toward the center of the pupil. These cells are opaque, meaning they block light. If the ingrowth is located in the periphery (the outer edge) of the cornea, the patient may not notice it at all. However, if the cells migrate into the visual axis, they cause significant glare, halos, and a drop in visual acuity that glasses cannot fix.

The Mechanism of Vision Loss

Epithelial ingrowth destroys vision in two ways. First, the physical presence of the opaque cells blocks light from reaching the retina. Second, and more commonly, the volume of the cells physically lifts the flap. This distorts the shape of the cornea, creating irregular astigmatism. The surface of the eye becomes bumpy rather than smooth. In severe cases, the cells can release enzymes that actually dissolve the stromal tissue, a condition known as "flap melt." This leads to permanent scarring and requires immediate intervention to save the structural integrity of the cornea.

Treatment: The "Lift and Scrape"

If the ingrowth is small, stable, and not affecting vision, doctors often choose to simply monitor it. The cells may eventually die off on their own. However, if the ingrowth is progressing or affecting vision, surgical removal is necessary. The surgeon brings the patient back to the operating room, lifts the LASIK flap, and meticulously scrapes the underside of the flap and the stromal bed to remove every single epithelial cell. Because these cells are sticky and stubborn, recurrence is a real risk. To prevent them from growing back, surgeons often use adjuvant treatments like applying a dilute alcohol solution to kill any remaining microscopic cells or placing sutures to seal the flap edge tightly during healing.

Risk Factors: Enhancements and Trauma

The single biggest risk factor for epithelial ingrowth is a LASIK enhancement. When a surgeon lifts a flap that has already healed (perhaps years later), the edge of the epithelium is disrupted, making it easier for cells to be dragged under the flap. Other risk factors include mild trauma to the eye (like a finger poke) that dislodges the flap edge, or dry eye syndrome, which prevents the epithelium from adhering quickly after the initial surgery.

FAQs on Epithelial Ingrowth

Is it painful?

Usually, no. It is typically painless. However, some patients report a persistent foreign body sensation, feeling like there is a grain of sand in the eye, or increased light sensitivity.

Can it happen with SMILE or PRK?

It is extremely rare in SMILE because there is no large flap, only a small incision. It is impossible in PRK because there is no flap at all; the epithelium grows over the surface naturally, not under it.

Does the YAG laser work?

Sometimes. For very small, isolated nests of cells, some doctors use a YAG laser to "zap" the cells without lifting the flap. This is less invasive but generally less effective than manual scraping for larger areas.

When to See Your Eye Doctor

If you have had LASIK in the past (even years ago) and you experience a sudden drop in vision or a feeling that something is in your eye after a minor injury, you need a slit-lamp exam. If an old flap has been moved, epithelial ingrowth can develop within days to weeks.

References

https://pubmed.ncbi.nlm.nih.gov/22265789/ https://eyewiki.aao.org/Epithelial_Ingrowth https://www.reviewofoptometry.com/article/manage-epithelial-ingrowth-after-lasik https://journals.lww.com/jrs/Abstract/2012/03000/Epithelial_ingrowth_after_LASIK.