JAN 07, 2014
This prospective study found that OCT-guided transepithelial phototherapeutic keratectomy (PTK) using a dual ablation excimer laser profile can provide favorable results and predictable refractive outcomes for scarring associated with Bowman layer irregularities.
This technique has the advantage of treating deeper corneal lesions without the hyperopic shift characteristic of standard PTK. However, more studies are needed to evaluate long-term results and stability.
The authors reviewed the charts of 22 patients with anterior corneal scarring associated with irregularities in the Bowman layer who had undergone transepithelial PTK according to a novel protocol. First they used anterior-segment OCT to determine the maximum depth of the opacity and crater. They then used the Allegretto Wavelight excimer laser to perform two corneal treatments, ensuring a minimum residual stromal bed of 275 µm. First, a myopic ablation pattern was performed through the epithelium to the depth of the opacity; then, a hyperopic ablation pattern was performed to control the refractive outcome. They applied mitomycin C 0.02% to the stromal bed for 15 seconds after both ablations.
At four months postop, all patients had gained at least one line of BSCVA. Preoperative and postoperative corneal topographic indices showed significant improvement in corneal cylinder (P = 0.0173) and projected visual acuity (P = 0.0261) but not in the surface asymmetry index (P = 0.0849) or the surface regularity index (P = 0.0543).
All subjects were within 1.5 D spherical equivalent of the target refractive outcome, and 23 percent were within 0.25 D of the target. No complications were associated with the treatment, and no patients required or desired subsequent treatment with either repeat PTK or with more invasive surgery, such as lamellar or penetrating keratoplasty.
The authors conclude that the OCT-guided transepithelial PTK algorithm described in this study can result in excellent visual and anatomic outcomes in patients with anterior corneal scars, particularly with crater formation. It may also restore the uniformity of the Bowman layer and normalize the epithelial thickness, thereby reducing postoperative residual irregular astigmatism. Future controlled studies are needed to further validate these results.