Corneal ectasia, tissue ablation amounts related, study finds

NICE, France — Posterior corneal ectasia following excimer laser treatment correlates with the amount of tissue ablated, according a poster presentation here at the European Society of Cataract and Refractive Surgeons meeting.

The purpose of the study, by Simona Filippo, MD, et al, was to find out if LASIK or LASEK procedures provoke iatrogenic posterior keratectasia, to evaluate the importance of these changes and to look for a relationship between the ectasia and the amount of refractive error treated or the residual corneal bed thickness.

The prospective study included 112 eyes of 61 patients, of which 83 eyes underwent LASIK and 29 underwent LASEK. Patients’ corneas were observed using Orbscan II (Bausch & Lomb) corneal topography preoperatively and at 1, 3, and 6 months after excimer treatment. The Technolas 117 laser (Bausch & Lomb) was used for ablation. The amount of the refractive correction ranged from –12 D to +4 D.

The authors concluded that both LASIK and LASEK induce posterior corneal ectasia that is measurable with the Orbscan II. Ectasia was noticeable at 1 month postop but tended to diminish at 3 and 6 months.

The amount of the posterior keratectasia correlated with the residual stromal bed thickness. Despite the presence of a greater residual corneal bed thickness in LASEK, the amount of keratectasia is not less important than in the LASIK cases, the researchers said.

Posterior corneal ectasia is also proportional to the change in spherical equivalent, according to the report. A greater correction correlates with a deeper ablation and causes a greater bulging forward, the authors said. The data demonstrate that the amount of posterior keratectasia is the same for LASIK and LASEK. However, the effect of the posterior corneal ectasia after excimer laser treatment on the quality of vision is still unknown. Further long-term studies are needed to understand the impact on sight, the authors said.