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Back-of-the-flap LASIK ablation may help prevent keratectasia in re-treatment
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PAMPLONA, Spain — Ablation of the undersurface of the LASIK flap may be an effective means of re-treatment for undercorrected patients with thin stromal beds.
The treatment, which seems to be effective for low residual refractive errors in eyes with sufficient flap stromal thickness, may help prevent keratectasia, according to a surgeon here.
Miguel Maldonado, MD, PhD, used the technique on 25 eyes with a spherical equivalent residual refraction after LASIK of between -0.75 D and -3.25 D and astigmatism of up to -1.5 D. He calculated that after enhancement on the back of the flap, the flap thickness in these eyes would be more than 150 µm, but with further ablation of the stromal bed the posterior stromal thickness would be less than 250 µm. Previous reports have noted that residual stromal thickness of less than 250 µm is a risk factor for corneal ectasia.
To perform undersurface ablation, Dr. Maldonado lifted the LASIK flap and had the patients turn their eyes downward, so that a visual axis mark on the corneal flap aligned with the laser beam. Mirror pattern ablations with an optical zone of 5 mm were performed on the flap stroma.
Follow-up ranged from 3 to 12 months. Mean pre-enhancement spherical equivalent of -2.05 D was reduced to -0.19 D at the last follow-up. Mean cylinder decreased from -0.48 D to -0.23 D after re-treatment.
Dr. Maldonado said satisfactory globe stabilization and stromal smoothness during ablation were more difficult to achieve than with conventional LASIK enhancements.
Average central flap thickness decreased from 187 µm before undersurface ablation to 164 µm at 1 month postop. No keratectasia developed.
“The UAF technique with flap thickness monitoring allows the surgeon to take advantage of the stromal tissue of the flap without compromising the integrity of the cap itself (Bowman's layer is kept intact) and eliminates further ablation of the residual posterior stroma,” Dr. Maldonado reports in the August issue of Ophthalmology.