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Thin-flap LASIK with a High-frequency, Low-energy, Small Spot
Femtosecond Laser – Effectiveness and Safety
Jérôme C Vryghem, Steven Heireman and Thibaut Devogelaere
Ophthalmologist and Eye Surgeon, Brussels Eye Doctors, Brussels, Belgium
Abstract Objective: To evaluate clinical results of a high-frequency, low-energy, small spot femtosecond laser for the creation of thin corneal
flaps in laser in situ keratomileusis (LASIK) used in a comparative case series at a private practice in Brussels, Belgium. Methods: A
series of 75 patients selected for LASIK refractive surgery were enrolled for treatment with the Ziemer FEMTO LDV femtosecond laser
and received a corneal flap of either 90 µm (59 patients, 103 eyes) or 80 µm (16 patients, 27 eyes) nominal thickness. Prospective
evaluation included flap dimensions, intra- and post-operative complications and visual outcomes. Results: Mean flap thickness was
89.03 (standard deviation [SD]: ± 8.26 µm) in the 90 µm group and 81.91 (SD ± 6.80 µm) in the 80 µm group. Mean uncorrected visual was
1.19 ± 0.26 in the 90 µm group and 1.10 ± 0.25 in the 80 µm group. Mean manifest refractive spherical equivalent was –0.12 ± 0.26 D in
the 90 µm group and –0.07 ± 0.31 D in the 80 µm group. There was no significant visual loss (≥2 lines loss of best corrected visual acuity)
in either group. One flap tear occurred in the 90 µm group (0.97 %) and two pseudo-buttonholes occurred in the 80 µm group (7.41 %).
No other clinically relevant complications occurred intra- or post-operatively. Conclusions: The Ziemer LDV femtosecond laser offers a
high degree of precision in the creation of 90 and 80 µm flaps for LASIK. Using this device for creating 90 µm flaps can be considered
a safe and effective procedure. A higher rate of complications were shown in 80 µm flaps.
Keywords Laser in situ keratomileusis (LASIK), femtosecond laser, thin corneal flaps, 80 µm and 90 µm corneal flaps
Disclosures: Part of this study was presented at the XXVI Congress of the European Society of Cataract and Refractive Surgeons, Berlin, Germany, September 2008 and
the American Society of Cataract and Refractive Surgery (ASCRS) Symposium on Cataract, IOL and Refractive Surgery, San Francisco, California USA, April 2009. This study
received no public or private financial support. Jérôme C Vryghem, Steven Heireman and Thibaut Devogelaere have no financial or proprietary interest in any product,
material or method mentioned.
Acknowledgements: Editorial assistance was provided by James Gilbart at Touch Medical Media, London, UK, with financial assistance from Ziemer Group.
Compliance with Ethical Guidance: Procedures were followed in accordance with the responsible committee on human experimentation and with the Helsinki
Declaration of 1975 and subsequent revisions. Informed consent was received from all patients involved in the study.
Received: 28 February 2014 Accepted: 10 November 2014 Citation: European Ophthalmic Review, 2014;8(2):99–103
Correspondence: Jérôme C Vryghem, Boulevard Saint-Michel, 12-16, B-1150 Brussels, Belgium. E-mail: [email protected]
Support: The publication of this article was supported by Ziemer Group. The views and opinions expressed are those of the authors and not necessarily those of Ziemer Group.
The best flap thickness has traditionally been considered to be 130 µm to
160 µm in order to preserve a greater amount of residual stromal bed
(RSB). The demand to correct larger amounts of ametropia, the development
of customised ablation techniques with a trend towards enlarging the
diameter of laser ablations, the inducement of aberrations by deep lamellar
keratectomies and the increasing incidence of post-laser in situ keratomileusis
(LASIK) corneal ectasia have caused surgeons to reconsider the ideal flap
thickness and to develop techniques for achieving thinner flaps. 1
Variability of flap thickness limits the reliability of calculations of RSB, which
can be critical in the correction of high myopia or LASIK in eyes with a
thin cornea. 1–5 A thin flap may thus be desirable: it enables the treatment
of higher corrections, permits larger ablation zones, induces fewer
aberrations, has a lower enhancement rate and better functional results
than a conventional >100 µm flap. Moreover, thin flaps help to maximise the
RSB – staying further away from the critical 250 µm barrier – and preserve
the biomechanical stability of the cornea, hence reducing the risk of ectasia.
A critical prerequisite for thin flaps to be a practical alternative is to use
a flap-making modality that creates flaps of uniform and predictable
thickness. Femtosecond lasers have been shown to meet this condition
© To u ch MEd ica l MEdia 201 4
better than mechanical microkeratomes. The practical limits of
femtosecond lasers are determined by the mechanical stability and
precision of the docking mechanism that applanates the cornea, by the
pulse energy, by the capability of the laser optics to focus the laser beam
in the cutting plane and finally by the quality of the achieved dissection.
A thinner than conventional flap blends the advantages of lamellar and
surface approaches: to preserve as much tissue as possible and at
the same time retain an intact flap for fast recovery and protection. 1,6,7
Sub-Bowman keratomileusis (SBK) is a laser procedure that involves
the use of a customised corneal flap between 90 and 110 µm with a
diameter that is closely matched to the ablation zone of the excimer laser
being used, typically ± 8.5 mm. 8
One of the principal concerns in thin-flap LASIK is that very thin flaps
induce the risk of intraoperative complications (pseudo-buttonhole): the
thinner the flap, the closer you get to Bowman’s layer. Ultra thin flaps are
more difficult to handle and more easily displaced enhancing the risk
of flap striae and irregular astigmatism. 9-11 Remaining tissue bridges can
cause force to be required for separating the flap, which may cause a
very thin flap to tear or to over-stretch.