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Br J Ophthalmol 96:1273-1274 doi:10.1136/bjophthalmol-2012-302037
  • PostScript
  • Letter

Laboratory model of bursting pressures of femtosecond laser-assisted penetrating keratoplasty wounds using novel pattern designs

  1. Bennie H Jeng1,2
  1. 1Department of Ophthalmology and Francis I. Proctor Foundation, University of California, San Francisco, USA
  2. 2Department of Ophthalmology, San Francisco General Hospital, San Francisco, California, USA
  1. Correspondence to Dr Bennie H Jeng, Department of Ophthalmology, University of California, San Francisco, 10 Koret Way, K-304, San Francisco, CA 94143-0730, USA; jengb{at}vision.ucsf.edu
  1. Contributors WG: substantial contributions to (1) conception and design, acquisition of data, and analysis and interpretation of data; (2) drafting the article; and (3) final approval of the version to be published. SDM: substantial contributions to (1) conception and design, and interpretation of data; (2) revising manuscript critically for important intellectual content; and (3) final approval of the version to be published. BHJ: substantial contributions to (1) conception and design, and interpretation of data; (2) revising manuscript critically for important intellectual content; and (3) final approval of the version to be published.

The femtosecond laser is being used with increasing popularity to create incisions for customised trephination in penetrating keratoplasty.1 Several femtosecond laser assisted keratoplasty (FLAK) pattern designs have been studied,2–5 all demonstrating superiority of various shaped cuts (particularly the Top-Hat) over traditional vertical trephination in resistance of the wound to leakage from elevated intraocular pressures (IOP).

One of the disadvantages, however, of the more popular FLAK patterns such as the Top-Hat, Mushroom and Zig-Zag, is that the diameter of either the anterior or the posterior corneal wound openings is relatively enlarged, effectively forcing the graft to encroach on the limbus (anteriorly) or the angle (posteriorly) and thereby increasing the risk for the associated complications of graft vascularisation, synechiae formation and elevated IOP. The purpose of this study was to evaluate wound leakage pressures in two FLAK patterns with nearly identical 8 mm anterior and posterior corneal diameters: the Dovetail 6 and the Bolt (a novel shape), and to compare these to the Top-Hat and traditional vertical cut patterns in a laboratory model.

Nineteen human corneoscleral rims were mounted on an artificial anterior chamber (Katena Products, Inc, Denville, New Jersey, USA) and 14 of the corneas were cut using a femtosecond laser (IntraLase, Abbott Medical Optics, Santa Ana, California, USA): Top-Hat (n=5), Dovetail (n=4) and Bolt (n=5) (online table 1) The remaining five corneas were trephinated with an 8 mm vertical handheld metal trephine. After the cuts were made, each corneal button was separated from the donor rim, replaced and secured with 16 interrupted 10-0 monofilament nylon sutures (figure 1). The maximal pressure that the wound could withstand prior to visualisation of any fluid emerging at the interface by an unmasked observer (IOPL) was measured utilising a 27-gauge infusion cannula and a 3-way connector to a digital manometer (Digimano 1000, Netech Corporation, Farmingdale, New York, USA).

Figure 1

High resolution Optical Coherence Tomography (Optovue Incorporated, Fremont, California, USA) image of (A) Dovetail pattern prior to separation, (B) Bolt pattern prior to separation and (C) Bolt pattern after separation.

The mean IOPL was 92.4 mm Hg (SD=9.61 mm Hg) for the Top-Hat group, 106.5 mm Hg (SD=15.2 mm Hg) for the Dovetail group, 84.6 mm Hg (SD=4.93 mm Hg) for the Bolt group and 38.2 mm Hg (SD=12.4 mm Hg) for the traditional group. The Dovetail, Bolt and Top-Hat groups all had a mean IOPL that was significantly higher than the mean IOPL of the traditional group (T-test, p <0.001). The mean IOPL of the Dovetail group was significantly higher than the Bolt group (T-test, p=0.015) but the mean IOPL of the Top-Hat group was not significantly different from the Bolt group (T-test, p=0.15) or from the Dovetail group (T-test, p=0.13).

Previous studies have consistently shown the Top-Hat design to achieve higher wound leakage pressures compared to other configurations, likely from the peripheral flange inherent in its design.2–5 However, the Top-Hat design incorporates a larger posterior corneal diameter bringing the donor tissue closer to the angle, increasing the risk of endothelial rejection and complications from glaucoma. Our study has demonstrated the wound leakage pressure of the Bolt and Dovetail designs are similar to that of the Top-Hat configuration, while maintaining the ability to have nearly identical anterior and posterior corneal diameters. The disadvantage of the Bolt design is that the current software for the femtosecond laser necessitates two separate cut parameters to be executed sequentially given the need to have two ring lamellar cuts and an additional side cut, an issue that is not encountered with the Dovetail design. Given its recent successful use in one published case6 as well as in three of our own cases (unpublished results), the advantage of having a nearly equal anterior and posterior diameter and the high wound leakage pressure, the Dovetail design may have practical value when full-thickness cornea transplantation is indicated.

Acknowledgments

The authors thank Sightlife, Inc (Seattle, WA) for providing corneas and AMO for providing cones for the femtosecond laser.

Footnotes

  • An additional table is published online only. To view this file please visit the journal online (http://dx.doi.org/10.1136/bjophthalmol-2012-302037).

  • The corresponding author had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

  • Funding Supported in part by a grant from That Man May See and Research to Prevent Blindness to the Department of Ophthalmology, University of California San Francisco.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

References