Femtosecond Laser-Assisted Keratoplasty (FLAK)
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Introduction
Corneal transplantation has undergone significant changes since the first successful penetrating keratoplasty in the early 20th century. Femtosecond Laser Assisted Keratoplasty (FLAK) is a corneal transplantation technique that utilizes femtosecond laser (FL) pulses to create precise incisions in both donor and recipient corneal tissue. This innovation allows for improved incision accuracy, leading to better graft alignment, wound stability, and overall visual outcomes.[1] The transition from manual trephination to FL customized cuts represents a major advance in corneal transplantation.
Patient Selection
Indications
Patients with corneal scarring, keratoconus, endothelial dysfunction, sequelae of infectious keratitis, or traumatic corneal opacities, in which sufficient tissue transparency remains to allow adequate laser penetration.[2,3] It’s particularly useful in patients who require earlier visual rehabilitation compared to conventional keratoplasty. [2,3,5]
Contraindications
Relative: Factors that compromise adequate laser delivery or wound healing, like irregular corneal surfaces, low corneal thickness, corneal edema, corneal vascularization, or opacification.[2,3,6]
Absolute: Conditions that interfere with or block laser penetration or safe tissue interaction.[2,3,6] Examples include severe opacity, active infection, corneal thinning, and inability to dock with FL machines.
Comparison with Conventional Keratoplasty
Traditional manual trephination relies on handheld instruments to create corneal incisions, often resulting in variability in wound architecture. In contrast, FLAK employs highly precise, reproducible incisions. This transition from manual to FLAK techniques enables different incisions, such as zig-zag, top-hat, and mushroom patterns, that enhance biomechanical stability through improved joining of donor and recipient tissues, ultimately promoting stronger wound integrity and more predictable healing.[4] Wound stenght is also higher and allows for better corneal biomechanics.
Principles of FLAK
FL produces tissue cuts with minimal damage to adjacent tissues. It has been utilized for the creation of refractive surgery flaps for LASIK, lens capsulotomy, and cataract fragmentation.5 In keratoplasty, FL has also been utilized to precisely trephine the host and donor corneas undergoing corneal lamellar transplantation, and to create surgical incisions for keratoplasty.
Overview of certain incision types made with FL: (Figure 1)
Top Hat: Allows for a wider endothelial surface than the anterior surface. Its configuration allows for better biomechanical strength and greater endothelium transplantation.
Mushroom: Has a larger anterior surface and less endothelium. Its configuration allows for better refractive exchanges while lowering the rejection rates.
Zig-Zag: Advantages of the zig-zag configuration include a better interaction between the donor and recipient corneas and reduced astigmatism. (Figure 2)
Surgical Technique
Femtosecond Laser–Assisted Penetrating Keratoplasty (F-PK)
Overview: Penetrating Keratoplasty (PK) involves a full-thickness exchange of the cornea. It was the earliest to be studied as a possible adjuvant point for FLAK. In the year 2000, an earlier study reported the use of FL to create corneal incisions for a PK. [6] F-PK involves the use of FL to create a full-thickness trephination, usually with a modified surgical incision type, like a mushroom incision. Both the donor and recipient cornea can be trephined to achieve matching incisions and provide a better interface for running sutures, allowing for earlier suture removal.[2,7]
Advantages of F-PK: The possibility to achieve stromal incision configurations like mushroom PK allows for the greater preservation of the healthy endothelium, while a wider anterior corneal radius permits lower rejection rates and better visual outcomes with the precision of FL.[8] F-PK achieves better visual and refractive astigmatism rates, better healing, and faster visual recovery when compared to manual PK.[9]
Femtosecond Laser-Assisted Deep Anterior Lamellar Keratoplasty (F-DALK)
Overview: Deep Anterior Lamellar Keratoplasty (DALK) allows for the exchange of the anterior cornea while preserving the Descemet’s membrane and the corneal endothelium. It is considered the standard for patients with intact endothelium. One of the most common complications of manual DALK includes the inadvertent perforation of the cornea while manually dissecting to reach the predescementic space.
Advantages of F-DALK: F-DALK allows for incision and correct depth for trephination. F-DALK allows the trephination to reach the desired zone and create the lamellar and posterior side cuts to create the bubble dissection with ease.[10] F-DALK has similar visual results as manual DALK but allows for an easier learning curve and lowers the risk of intraoperative perforations and conversion to PK while performing the trephination. [11,12]
Femtosecond Laser–Assisted Descemet Membrane Endothelial Keratoplasty (F-DMEK)
Overview: Descemet Membrane Endothelial Keratoplasty (DMEK) enables precise exchange of the innermost corneal endothelial layer.[13] F-DMEK allows better graft preparation, side cut incisions, and descemetorhexis in DMEK surgery.[14] DMEK carries a higher rebubbling rate than DSAEK.
Advantages of FLAK: No significant differences were found with failure rates or visual acuity, but F-DMEK is associated with lower graft detachment rates, rebubbling rates, and endothelial cell loss.[15]
Femtosecond Laser-Assisted Descemet's Stripping Automated Endothelial Keratoplasty (F-DSAEK)
Overview: Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK) involves the transplantation of the corneal endothelium and the posterior stroma. F-DSAEK uses FL to trephine the host cornea or helping eyebanking to create a better donor tissue.
Complications
Intraoperative: The most critical technical issue is suction loss during the procedure, which can result in incomplete cuts of the interface. Decentration of the laser pattern, usually caused by patient movement or improper alignment during the initial docking phase, can lead to an asymmetrical interface.
Postoperative: Wound dehiscence can occur if sutures are removed prematurely. Graft rejection and infection are the most significant threats to long-term success. In lamellar procedures, patients may experience interface haze, which can limit final visual acuity despite a clear graft.
References
1. Farid M, Steinert R, Gaster R. Comparison of Penetrating Keratoplasty Performed with a Femtosecond Laser Zig-Zag Incision versus Conventional Blade Trephination Ophthalmology. 2009;116:1638-1643. 2. Chamberlain WD, Rush SW, Mathers WD, Cabezas M, Fraunfelder FW. Comparison of femtosecond laser-assisted keratoplasty versus conventional penetrating keratoplasty. Ophthalmology. 2011;118(3):486-491. doi:10.1016/j.ophtha.2010.08.002 3. Baqalaqil D, Alrayes RS, Khan AA, et al. Comparing the Efficacy and Safety of Femtosecond Laser-Enabled Keratoplasty and Conventional Penetrating Keratoplasty: A Systematic Review and Meta-Analysis. Clin Ophthalmol. 2025;19:3793-3806. doi:10.2147/OPTH.S538399 4. Hieda O. Femtosecond Laser-Assisted Keratoplasty. 2013. Accessed April 5, 2026. https://www.jstage.jst.go.jp/article/jslsm/34/1/34_37/_pdf/-char/en 5. Liu C, Mehta JS, Liu YC. Femtosecond laser-assisted corneal transplantation. Taiwan J Ophthalmol. 2023;13(3):274-284. doi:10.4103/tjo.TJO-D-23-00080 6. Roszkowska AM, Urso M, Signorino A, Aragona P. Use of the femtosecond lasers in ophthalmology. EPJ Web Conf. 2018;167:05004. doi:10.1051/epjconf/201816705004 7. Bahar I, Kaiserman I, Lange AP, et al. Femtosecond laser versus manual dissection for top hat penetrating keratoplasty. Br J Ophthalmol. 2009;93(1):73-78. doi:10.1136/bjo.2008.148346 8. Bergamaschi P, Busin LML, Yu AC, Busin M. Mushroom penetrating keratoplasty: A narrative review. J Clin Med. 2025;14(7):2351. doi:10.3390/jcm14072351 9. Kamiya K, Kobashi H, Shimizu K, Igarashi A. Clinical outcomes of penetrating keratoplasty performed with the VisuMax femtosecond laser system and comparison with conventional penetrating keratoplasty. PLoS One. 2014;9(8):e105464. doi:10.1371/journal.pone.0105464 10. Siebelmann S, Händel A, Matthaei M, Cursiefen C, Bachmann B. Femtosecond laser-assisted (triple-)deep anterior lamellar keratoplasty with a novel liquid interface. J EuCornea. 2020;8:14-17. doi:10.1016/j.xjec.2020.06.001 11. Alio JL, Abdelghany AA, Barraquer R, Hammouda LM, Sabry AM. Femtosecond laser assisted deep anterior lamellar keratoplasty outcomes and healing patterns compared to manual technique. Biomed Res Int. 2015;2015:397891. doi:10.1155/2015/397891 12. Gadhvi KA, Romano V, Fernández-Vega Cueto L, et al. Femtosecond laser-assisted deep anterior lamellar keratoplasty for keratoconus: Multi-surgeon results. Am J Ophthalmol. 2020;220:191-202. doi:10.1016/j.ajo.2020.07.023 13. Melles GRJ, Ong TS, Ververs B, van der Wees J. Descemet membrane endothelial keratoplasty (DMEK). Cornea. 2006;25(8):987-990. doi:10.1097/01.ico.0000248385.16896.34 14. Arnalich-Montiel F, Aguado-Casanova V, Vicente-Antolin M, Muñoz-Negrete FJ. Effect of femtosecond-assisted vs manual descemetorhexis on the posterior corneal surface after DMEK: A fellow eye comparison. Eur J Ophthalmol. 2026;36(2):224-230. doi:10.1177/11206721251379938 15. Sorkin N, Gouvea L, Din N, et al. Five-year safety and efficacy of femtosecond laser-assisted Descemet membrane endothelial keratoplasty. Cornea. 2023;42(2):145-149. doi:10.1097/ICO.0000000000003019
