Intrastromal lamellar femtosecond laser keratoplasty with superficial flap

Lamellar keratoplasty has usually been performed taking a trephine to delineate the extent of the tissue to be excised, and a knife or similar instrument to remove the lamellar corneal tissue from the underlying deep corneal bed. In a similar way, the lamellar donor tissue was prepared and inserted into the recipient bed. The depth of the lamellar excision extended from the corneal epithelial surface to the deep corneal stroma. Marked disadvantages of the technique have been pronounced corneal astigmatism and optical insufficiencies of the interface between the lamellar graft and the recipient corneal bed caused by irregularities of both surfaces. The purpose of the present report was to describe the new femtosecond laser technology,^1–3 which may enable us to perform a new type of intrastromal lamellar keratoplasty with preservation of an intact Bowman’s layer and regular corneal epithelium.

Case report

Using a corneal contact lens and a femtosecond laser (20/10 Perfect Vision, Am Taubenfeld 21/1, D-69123 Heidelberg, Germany) with a wavelength of 1060 nm, a spot size of about 10 μm, and a laser pulse duration of several hundred femtoseconds, a pre-descemetal incision running parallel to the corneal surface was created in five postmortem eyes of slaughterhouse pigs. The diameter of the deep stromal incision was 7 mm. In a second step, a circular sagittal incision was performed starting from the peripheral edge of the already existing incision in the pre-descemetal level to the superficial layer of the corneal stroma. In continuation of the latter sagittal incision, a corneal flap was prepared with a diameter of 7 mm, a thickness of about 100 μm, a hinge, and three positional pikes.⁴ The pikes in the flap with the corresponding notches in the bed of the flap were formed to increase the rotational stability of the flap after repositioning. The height of the peaks was about 0.40 mm. After opening of the flap the intrastromal segment situated between the pre-descemetal incision and the incision in the superficial stromal level was removed and exchanged against a similar formed segment obtained from another (donor) pig eye. In a final step, the flap was repositioned.

For all eyes included in the study, the intrastromal corneal button and the superficial flap with the three positional pikes could be prepared without major difficulties. The corneal buttons could easily be repositioned into their original beds as well as into the recipient beds of other eyes in which the recipient beds were created with the same diameter as the donor button. The time taken for preparation of the intrastromal corneal button and the corneal flap, and for the exchange of the corneal buttons was less than 10 minutes in all cases.

Comment

Femtosecond laser technology allows a new type of intrastromal lamellar keratoplasty with removal of a mid-stromal segment and preservation of an intact Bowman’s membrane. Considering the decreased amount of allogenic corneal tissue transplanted, and regarding the preservation of the original corneal surface, lamellar intrastromal femtosecond laser keratoplasty may be associated with a smaller rate of immunological graft reaction and with a lower postoperative corneal astigmatism in some eyes. Future clinical studies may show whether positional edges in the superficial flap increase its postoperative rotational stability.