Healing process at the flap edge in its influence in the development of corneal ectasia after LASIK

Post-laser in situ keratomileusis (LASIK) corneal ectasia is a progressive deformation of the gross corneal anatomy that occurs after surgery. However, this is a rare event even after deep lamellar keratoplasty. We hypothesize that the strength of the lamellar keratoplasty wound is derived from the sutures that enhance the wound edge healing response. This study compares, in a rabbit model, the stability of previously sutured and unsutured microkeratome flaps.

Unilateral 160-micro m-thick LASIK flaps using a mechanical microkeratome was performed in 20 rabbit eyes. Animals were then divided in two groups: In group A, the flap was left without sutures. In group B, the flap was sutured with 12 interrupted 10/0 nylon stitches that were removed after 3 weeks under general anesthesia. Six weeks after surgery, all rabbits had corneal topographies performed at their baseline intraocular pressure (IOP) (14 mmHg) and at two artificially increased pressures (25 and 45 mmHg) using an anterior chamber maintainer implanted in the inferior limbal area. The animals were humanely euthanized, and immunohistological analysis of the corneas was performed.

A delta K1 value, which indicates the difference in the simulated keratometric value at baseline and the one measured at 25 mmHg, was calculated for all eyes. It showed a mean steepening effect of 2.74 D +/- 0.38 D in group A compared with 1.08 D +/- 0.27 D in group B (p < 0.05). Similarly, a delta K2 value, which indicates the difference in the simulated keratometric value at baseline and the one obtained at 45 mmHg, was registered. It showed a mean steepening effect of 3.02 D +/- 0.87 D in group A compared with 0.75 D +/- 0.44 D in group B (p < 0.05). Six weeks after surgery, the peripheral flap interface in group B consisted of 14.3% +/- 4.15% of positive monoclonal mouse anti-alpha smooth muscle actin (alpha-SMA) cells compared with 4.18 +/- 3.76% in group A (p < 0.05).

The addition of sutures in the corneal flap after LASIK appears to reduce the amount of corneal steepening when the IOP is artificially increased up to 25 mmHg in this rabbit model. Our results suggest that an increase in the amount of myofibroblastas induced by the sutures may be responsible for this behavior. Corneal ectasia may be related to the clinically observed lack of corneal wound-healing at the edge of the flap that allows the cornea to bulge. By stimulating a stronger wound-healing response at the edge of the flap, the cornea may better resist steepening under increased IOP conditions and improve the long-term stability of LASIK surgery in borderline thin corneas.