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Post-PRK stromal wound repair associated with myopic regression, haze

Invest Ophthalmol Vis Sci. 2009;50(5):2061-2066.

Issue: September 10, 2009

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PRK and LASIK spurred increased epithelial thickness, but PRK resulted in more dramatic stromal regrowth.

“Initial changes in stromal thickness (after PRK) and total corneal thickness (after PRK or LASIK) appear to contribute to postoperative refractive regression,” the study authors said. “In contrast, the increase in epithelial thickness seems to have no refractive impact.”

The randomized study included 46 patients assigned to undergo LASIK (25 patients) or PRK (21 patients). Preoperatively, all patients had spherical equivalent refraction of –6 D to –8 D, less than –1.5 D of astigmatism and monocular best corrected visual acuity of 0.10 or more logMAR units.

Manifest refraction and confocal microsopy were undertaken before surgery and at 1, 3, 6, 12 and 36 months after surgery. Central corneal thickness, epithelial thickness, stromal thickness, LASIK flap thickness and stromal bed thickness were assessed.

Study results showed a weak correlation between total corneal thickness and changes in spherical equivalent refraction 1 week to 3 years after LASIK. One week to 1 year after PRK, changes in refraction were associated with increased total corneal thickness and stromal thickness, confirming previous reports linking increased wound healing to myopic regression and haze, the authors said.

“To better evaluate the relation between wound repair and postoperative refractive changes, topographic variations in corneal sublayer thickness over time should be determined,” they said.

It is no surprise that the “initial changes in stromal thickness (after PRK) and total corneal thickness (after PRK or LASIK) appear to contribute to postoperative refractive regression.” The one surprise is that the increase in epithelial thickness had no refractive impact. Perhaps the newer, wider ablation zones and smoother transition zones are making extreme epithelial hyperplasia a thing of the past.

– Marguerite B. McDonald, MD
OSN Refractive Surgery Board Member