ArticlePDF AvailableLiterature Review

Femtosecond Laser Technology in Corneal Refractive Surgery: A Review

Authors:
  • London Vision Clinic

Abstract and Figures

To discuss current applications and advantages of femtosecond laser technology over traditional manual techniques and related unique complications in corneal refractive surgical procedures, including LASIK flap creation, intracorneal ring segment implantation, astigmatic keratotomy, presbyopic treatments, and intrastromal lenticule procedures. Literature review. From its first clinical use in 2001 for LASIK flap creation, femtosecond lasers have steadily made a place as the dominant flap-making technology worldwide. Newer applications are being evaluated and are increasing in their frequency of use. Femtosecond laser technology is rapidly becoming a heavily utilized tool in corneal refractive surgical procedures due to its reproducibility, safety, precision, and versatility.
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912
Copyright © SLACK Incorporated
REVIEW
he femtosecond laser is a focused infrared laser with a
wavelength of 1053 nm that uses ultrafast pulses with a
duration of 100 fs (10010
-15
seconds). It is a solid-state
Nd:Glass laser similar to an Nd:YAG laser, which operates on the
principle of photoionization (laser-induced optical breakdown),
producing photodisruption at its focal point, resulting in a rap-
idly expanding cloud of free electrons and ionized molecules
(plasma). Small volumes of tissue are vaporized with the forma-
tion of cavitation gas bubbles consisting of carbon dioxide and
water, which eventually dissipate into the surrounding tissues.
1
In this process, collateral damage seen with a femtosecond laser
is 106 times less than an Nd:YAG laser, thus demonstrating its
precision and safety when used in corneal surgeries.
2
The technology of the femtosecond laser was fi rst introduced
in late 2001 and technological evolution has resulted in a grad-
ual increase in its higher laser fi ring frequency, which recently
reached 500 kHz from its original 6 kHz.
3-5
The higher laser
frequency permits lower energy per pulse and tighter line sep-
aration, which leads to smoother corneal stromal bed creation.
Currently, fi ve femtosecond laser systems are commercially
available: 1) IntraLase (Abbott Medical Optics Inc, Santa Ana, Cal-
ifornia); 2) Femtec (20/10 Perfect Vision, Heidelberg, Germany);
3) Femto LDV (Ziemer Ophthalmic Systems, Port, Switzer-
land); 4) VisuMax (Carl Zeiss Meditec AG, Jena, Germany); and
5) WaveLight FS200 (Alcon Laboratories Inc, Ft Worth, Texas).
Current laser platforms differ in pulse energy and frequency,
applanation surface (fl at or curved), laser delivery (raster or
spiral pattern), available applications, and mobility (Table 1).
4
There are a wide range of available and evolving femto-
T
ABSTRACT
PURPOSE: To discuss current applications and advan-
tages of femtosecond laser technology over traditional
manual techniques and related unique complications in
corneal refractive surgical procedures, including LASIK
ap creation, intracorneal ring segment implantation,
astigmatic keratotomy, presbyopic treatments, and intra-
stromal lenticule procedures.
METHODS: Literature review.
RESULTS: From its fi rst clinical use in 2001 for LASIK
ap creation, femtosecond lasers have steadily made a
place as the dominant fl ap-making technology worldwide.
Newer applications are being evaluated and are increas-
ing in their frequency of use.
CONCLUSIONS: Femtosecond laser technology is
rapidly becoming a heavily utilized tool in corneal re-
fractive surgical procedures due to its reproducibil-
ity, safety, precision, and versatility. [J Refract Surg.
2012;28(12):912-920.]
doi:10.3928/1081597X-20121116-01
From the Department of Ophthalmology, University of Crete, Medical School,
Heraklion, Greece (Kymionis, Kankariya, Plaka); London Vision Clinic,
London, United Kingdom (Reinstein); and the Department of Ophthalmology,
Columbia University Medical Center, New York, New York (Reinstein).
Dr Reinstein is a consultant for Carl Zeiss Meditec, has a proprietary interest
in the Artemis technology (ArcScan Inc), and is an author of patents related
to VHF digital ultrasound administered by the Cornell Center for Technology
Enterprise and Commercialization, Ithaca, New York. The remaining authors
have no financial or proprietary interest in the materials presented herein.
Correspondence: George D. Kymionis, MD, PhD, University of Crete,
Medical School, 71003 Heraklion, Crete, Greece. Tel: 30 28 1039 4656;
Fax: 30 28 1039 4653; E-mail: kymionis@med.uoc.gr
Received: July 19, 2012; Accepted: October 18, 2012
Femtosecond Laser Technology in Corneal
Refractive Surgery: A Review
George D. Kymionis, MD, PhD; Vardhaman P. Kankariya, MD; Argyro D. Plaka, MD;
Dan Z. Reinstein, MD, MA(Cantab), FRCSC, FRCOphth, FEBO
913
Journal of Refractive Surgery • Vol. 28, No. 12, 2012
Femtosecond Laser Applications/Kymionis et al
second laser applications in the fi eld of refractive sur-
gery, with LASIK fl ap creation being the most utilized.
Additional procedures include astigmatic keratotomy
(AK), channel creation for implantation of intrastromal
corneal ring segments (ICRS), intrastromal lamellar
pocket creation for the insertion of intracorneal inlays
for the treatment of presbyopia, femtosecond lenticule
extraction (FLEx), small-incision lenticule extrac-
tion (SMILE), and intrastromal presbyopia correction
(INTRACOR), and these are likely to expand in the fu-
ture. In addition to expansion of femtosecond laser ap-
plications in corneal refractive surgery, technological
advances should also lead to an improvement in the
safety and effi cacy of the procedures.
LASIK FLAP CREATION
Corneal fl ap creation in LASIK is the most common
application of the femtosecond laser in corneal refrac-
tive surgery. More than 55% of all LASIK procedures
in the United States were performed with femtosecond
lasers in 2009.
4
The proportion is even greater in high-
volume practices, and femtosecond lasers are gaining
more acceptance worldwide. When using femtosec-
ond technology for fl ap creation, each pulse of the la-
ser causes the generation of a small amount of micro-
plasma at its focal point in the corneal tissue leading
to formation of microscopic gas bubbles, which then
dissipate into surrounding tissue. These pulses, when
applied adjacent to each other in a raster pattern, re-
sult in a cleavage plane to create the lamellar cut. More
pulses are then applied in a peripheral circular pattern
to create the vertical side cuts, thus creating a LASIK
ap. The fl ap can then be lifted for excimer laser ab-
lation. Recently introduced higher laser fi ring speeds
(eg, IntraLase FS 150, WaveLight FS200, VisuMax 500)
have reduced the energy requirements, thus reducing
the cavitation bubble size and duration, tissue infl am-
mation, time of fl ap creation, and ease of fl ap lifting.
5
The major advantages of femtosecond laser fl ap
creation compared to mechanical microkeratomes
(Table 2) are reduced incidence of fl ap complications
(eg, buttonholes, epithelial abrasions, short and ir-
regular fl aps), greater surgeon choice of fl ap diameter,
thickness, side-cut angle, hinge position and length,
increased precision with improved fl ap safety and
thickness predictability, and capability of cutting thin-
ner fl aps (Fig 1) to accommodate thin corneas and high
refractive errors.
6-10
Additional advantages include
stronger fl ap adherence and therefore less infl uence by
trauma, fewer induced higher order aberrations, better
contrast sensitivity, lesser need for retreatment, lesser
rate of epithelial ingrowth, and lesser incidence of dry
eye.
10-14
Femtosecond laser–created fl aps are planar in
architecture as opposed to most microkeratome fl aps,
8
which have been shown to possess signifi cant variabil-
ity in the thickness profi le.
15
This is important as uni-
formity of fl ap thickness may also affect the predictabil-
ity of excimer laser stromal photoablation as stromal
anatomy, hydration, and ultraviolet absorbance varies
with corneal depth.
6,16
Visual and refractive outcomes
of femtosecond laser–assisted LASIK demonstrate ex-
cellent safety and effi cacy, with most studies reporting
equivalence with microkeratome LASIK.
17
With the
current acceptance and future promise of femtosecond
lasers, it will more than likely be the dominant tech-
nology used globally for fl ap creation in LASIK.
TABLE 1
Comparison of Commercially Available Femtosecond Lasers
Parameter IntraLase iFS 150 Femto LDV Zeiss VisuMax FemTec 2010 WaveLight FS200
Laser type Amplifier Oscillator Fiber optic amplifier Amplifier Oscillator-amplifier
Wavelength (nm) 1053 1045 1043 1053 1045
Laser pattern Raster Segmental Spiral Spiral Raster
Centration Computer Mechanical Mechanical Mechanical Computer
Visualization of surgery Visual and virtual Virtual Visual Visual Visual and virtual
Mobile No Yes No No No
Suction Single syringe Single built in Single built in on
limbus
Single built in Dual built in
Applanation surface Planar Planar Curved Curved Modified planar
Additional procedures AK, Wedge, LK, PKP,
ICRS, Biopsy, Pocket
LK, PKP, Pocket,
ICRS
FLEx, SMILE AK, LK, PKP, ICRS,
INTRACOR
AK, LK, PKP, ICRS
AK = astigmatic keratotomy, LK = lamellar keratoplasty, PKP = penetrating keratoplasty, ICRS = intracorneal ring segments, FLEx = femtosecond lenticule
extraction, SMILE = small-incision lenticule extraction
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Femtosecond Laser Applications/Kymionis et al
Femtosecond lasers promise excellent reproduc-
ibility and versatility in applications, but at the same
time they demonstrate a unique set of complications.
18
Confl uent cavitation bubbles during intrastromal treat-
ment (opaque bubble layer) may confound the ability
of the surgeon and the excimer laser eye tracker device
to locate the pupil for centration purposes. Gas bubbles
routinely accumulate in the fl ap interface during femto-
second laser treatment, but occasionally they may dis-
sect into the deep stromal bed, resulting in a posterior
stromal opaque bubble layer that does not escape when
the fl ap is lifted.
19
In rare instances, bubbles may escape
into the corneal subepithelial space and larger central
vertical gas breakthrough may potentially result in a
ap buttonhole.
20,21
Posterior vertical gas breakthrough
may result in air bubbles in the anterior chamber.
22
Another complication of femtosecond laser–assisted
LASIK is transient light sensitivity syndrome,
23,24
which may occur days to weeks after the procedure
and is characterized by extreme photophobia with
good visual acuity and absence of clinical fi ndings on
examination. It resolves within a few weeks after being
treated with an aggressive course of topical corticoste-
roids. After femtosecond laser–assisted LASIK, “rain-
bow glare” is an optical phenomenon experienced
as colored bands of light radiating from a white light
source when viewed in a dark environment.
25
The
proposed mechanism is diffraction of light by micro-
irregularities on the back surface of the femtosecond
laser–created LASIK fl ap.
Diffuse lamellar keratitis (DLK) after LASIK femto-
second laser–enabled fl ap creation tends to have little
effect on visual acuity and is associated with a higher
energy level for fl ap creation and larger fl ap diameter.
26
Mild transient lamellar keratitis limited to the periph-
ery is still encountered occasionally, perhaps causally
related to the higher energies used for making the ver-
tical side cuts. This type of DLK is likely attributable to
photodisruption-induced microscopic tissue injury ag-
gravated by ocular surface infl ammatory mediators.
27,28
Another likely etiology is damage to the epithelium at
the site of the side cut and release of proinfl ammatory
cytokines from the damaged epithelial cells. Hainline
et al
29
reported central lamellar fl ap necrosis following
TABLE 2
Comparison of Microkeratomes and Femtosecond Lasers for LASIK Flap Creation
Parameter Microkeratome Femtosecond Laser
Flap shape Meniscus Planar
Flap/hinge diameter Keratometry dependent Computer control
Flap thickness Dependent on pachymetry, keratometry, IOP,
blade quality and translational speed
Computer control
Thickness predictability Moderate High
Side cut Shallow angled Computer control
Epithelial ingrowth More than femtosecond laser flaps Less
Unique complications Flap buttonhole Opaque bubble layer, vertical gas break-
through, transient light sensitivity syndrome,
rainbow glare
IOP = intraocular pressure
Figure 1. Horizontal nongeometrically cor-
rected Artemis very high-frequency digi-
tal ultrasound (ArcScan Inc, Morrison,
Colorado) B-scan of a cornea after the
creation of a 95-µm LASIK flap using the
VisuMax femtosecond laser.
915
Journal of Refractive Surgery • Vol. 28, No. 12, 2012
Femtosecond Laser Applications/Kymionis et al
the use of a femtosecond laser. It appears to differ from
DLK because the location of stromal infl ammation is
in the fl ap anterior stroma and corticosteroid treatment
seemed to have little effect on outcomes.
Loss of suction during femtosecond laser fl ap cre-
ation is usually not as serious a complication as with
a mechanical microkeratome, and the suction ring
may be reapplied and treatment resumed immediately
in many cases. If suction is lost during the side-cut
phase, a new side cut is made just inside the diameter
of the interface cut.
30
It is important to note fl aps cre-
ated with a femtosecond laser may be harder to lift at
the time of retreatment, and therefore if retreatment is
necessary, it should be attempted early after the initial
procedure.
31
Other reported complications include gas
bubble under the conjunctiva, unintended epithelial
ap, interface haze, interface stromal irregularities,
and macular hemorrhage.
32-36
INTRASTROMAL CORNEAL RING SEGMENT
IMPLANTATION
Intrastromal corneal ring segments are crescent-shaped
polymethylmethacrylate implants originally designed to
correct low to moderate myopia.
37
Currently, they are
used to treat postoperative LASIK corneal ectasia,
38
pel-
lucid marginal degeneration,
39
and keratoconus.
40
Intrastromal corneal ring segments are inserted in
intrastromal channels (created either manually or us-
ing a femtosecond laser) at 75% depth of the thinnest
pachymetry. This results in an arc shortening effect
and redistribution of corneal peripheral lamellae to
produce fl attening of the central cornea.
41
Their effect
is proportional to the thickness of the implant and in-
versely proportional to the implant diameter.
42
Com-
pared to the manual technique, a femtosecond laser
makes tunnel creation faster, easier, and more repro-
ducible and offers accurate tunnel dimensions (width,
diameter, and depth).
43
With mechanical dissectors,
segment depth may be shallower at positions further
from the incision but depth is consistent throughout
when using a femtosecond laser.
44
The surgical procedure with a femtosecond laser, as
in the mechanical procedure, is typically performed
under topical anesthesia.
45
After marking a reference
point (pupil center or fi rst Purkinje refl ex) on the cor-
nea and measuring the corneal thickness by ultrasonic
pachymetry at the area of implantation (5-mm diam-
eter), the disposable suction ring of the femtosecond
laser system is centered. The disposable glass lens is
applanated to the cornea to fi xate the eye and help
maintain the precise distance from the laser head to
the focal point. An entry cut with the femtosecond la-
ser is created with the aim of allowing access for ring
placement in the tunnel. The tunnel is then created at
approximately 70% to 80% of the corneal thickness.
Intrastromal corneal ring segments are inserted in the
created tunnels (Fig 2).
Theoretically, compared with mechanical tunnel
creation, which is based on surgeon skill, the fem-
tosecond laser–assisted procedure should generate
a more accurate stromal dissection, leading to better
visual and refractive results. However, similar visual
and refractive outcomes with both procedures were re-
ported over short-term follow-up in eyes with kerato-
conus and postoperative LASIK ectasia.
46,47
Kubaloglu
et al
43
compared the clinical outcomes of keratoconic
patients treated with two types of ICRS. Both implants
were safe and effective and no difference was observed
in visual or refractive outcomes when comparing me-
chanical microkeratome– and femtosecond laser–cre-
ated channels. They also reported that the use of the
femtosecond laser made the procedure faster, easier,
and more comfortable for the patient. Further expe-
rience and the development of more accurate nomo-
grams should improve clinical outcomes.
Complications associated with the mechanical tech-
nique include epithelial defects, anterior or posterior
perforation with the mechanical spreader, shallow or
uneven placement of the ICRS, decentration, extension
of the incision towards the central cornea or limbus,
and corneal stromal edema around the incision and
channel from surgical manipulation.
48,49
Most cases of
extrusion have been observed in eyes implanted using
mechanical dissection; however, three cases of ring ex-
trusion in advanced keratoconus and one case of seg-
ment migration to the incision site have been reported
with femtosecond laser channel creation.
45
Figure 2. Slit-lamp photograph demonstrating two intrastromal corneal
ring segments (arrows) placed in a channel created with a femtosecond
laser for the treatment of keratoconus.
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Femtosecond Laser Applications/Kymionis et al
Coskunseven et al
50
reported complications after
implantation of ICRS in keratoconic patients using the
IntraLase femtosecond laser stating that intraoperative
incomplete channel creation (2.7%) and postopera-
tive segment migration (1.3%) were the most common
complications. The study also demonstrated intraop-
erative adverse events such as galvanometer lag error
(0.6%), endothelial perforation (0.6%), and vacuum
loss (0.1%) and postoperative complications such as
superfi cial movement of the segments (0.1%), corneal
melting (0.2%), and infection (0.1%).
ASTIGMATIC KERATOTOMY
Femtosecond lasers have recently been used for
the correction of natural or postoperative lamellar/
penetrating keratoplasty (PK) corneal astigmatism.
51-56
Corneal astigmatism is a common fi nding after PK and
may cause signifi cant visual impairment. Possible
causes are scar formation, corneal thickness mismatch
between the graft and recipient tissue and irregular
forces created by sutures.
57
Astigmatic errors after
PK may be corrected with several surgical techniques
such as refractive procedures (LASIK, photorefractive
keratectomy), relaxing incisions, compression sutures,
and wedge resections.
58,59
Astigmatic keratotomy is
a simple, safe, and minimally invasive technique.
Therefore, AK is the most commonly used method for
the reduction of high amounts of astigmatism in post-
operative PK patients.
60-63
The technique is similar to
limbal relaxing incisions, with incisions placed inside
the donor-recipient junction as it behaves like a new
limbus due to a fi brotic ring formed as part of the heal-
ing response. Astigmatic keratotomy should only be
performed after all corneal sutures are removed.
Astigmatic keratotomy may be performed manually
with a diamond knife as well as with a femtosecond
laser. Major limitations of manual AK are technical
diffi culties (especially in nonorthogonal astigmatism),
compromised reproducibility, unpredictability, and
complications such as wound dehiscence, epithelial
abrasions, and perforation.
60-64
Compared with the me-
chanical method, the use of a femtosecond laser offers
the advantages of higher precision and stability as well
as more accurate planning of the length, depth, and op-
tical zone of the cuts (Fig 3).
52
Femtosecond laser AK
has been reported to be effective in reducing astigma-
tism and improving uncorrected (UDVA) and corrected
distance visual acuity (CDVA).
64
Yoo et al
65
reported the
use of anterior segment optical coherence tomography
(AS-OCT) as a guide for the planned incision depth. In
particular, in postoperative Descemet stripping endo-
thelial keratoplasty (DSEK) patients, it is important to
evaluate AS-OCT so as not to include the DSEK donor
lenticular thickness for pachymetry measurements as
this will lead to inadvertent recipient full-thickness in-
cision and signifi cant overcorrection. In postoperative
DSEK eyes, the aim should be for the incisions to be up
to 90% of the recipient corneal thickness only.
PRESBYOPIA TREATMENT
Femtosecond lasers are now also used for the cre-
ation of intrastromal pockets to insert biocompatible
intracorneal inlays for the treatment of presbyopia.
66
Intracorneal inlays are available with different mecha-
nisms including refractive intracorneal inlays, which
have an annular refractive zone for near vision, where-
as other intracorneal inlays have no refractive power
and work by increasing the curvature in the center of
the pupil; in addition, pinhole intracorneal inlays en-
able near vision by taking advantage of the pinhole ef-
fect. Intracorneal inlays are inserted in the nondomi-
nant eye either under a LASIK fl ap or into a stromal
pocket created by a femtosecond laser.
Implantation of intracorneal inlays has been de-
scribed for the treatment of presbyopia and hyperopia
using corneal fl aps created by mechanical microkera-
tomes
66,67
or femtosecond lasers
68,69
or corneal pockets
created by mechanical microketatomes.
70
Femtosec-
ond laser–assisted intracorneal pocket creation could
increase the precision of the inlay position by custom-
ization of depth and length of the tunnel, which could
enhance the predictability, resulting in better fi nal
outcomes and improving the safety of the procedure
(Fig 4). The development of special software for cus-
tomized pockets could further simplify and increase
the effi cacy of the procedure. Prospective comparative
studies are needed to evaluate the long-term results of
Figure 3. Slit-lamp photograph demonstrating astigmatic keratotomy
incisions (arrows) performed with a femtosecond laser for naturally occur-
ring astigmatism.
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Journal of Refractive Surgery • Vol. 28, No. 12, 2012
Femtosecond Laser Applications/Kymionis et al
the technique and optimize the laser parameters. In ad-
dition, there is no need to change or add new equip-
ment in a modern refractive surgery center, except to
obtain the special injector and mask.
70,71
In addition to pocket creation for inlay implantation,
femtosecond lasers are being used in INTRACOR as fi rst
described by Ruiz et al.
72
The INTRACOR procedure is
a femtosecond laser–based incisional method for intra-
stromal correction of presbyopia using the Technolas
520FS (previously Femtec [Technolas Perfect Vision
GmbH, Munich, Germany]) femtosecond laser plat-
form. During INTRACOR, two to four cylindrical ring
incisions are created in the corneal stroma aiming to
change its biomechanical properties and induce a cen-
tral hyperprolate region for the treatment of presbyopia.
Studies have shown improved uncorrected near visual
acuity (range: J1 to J2) with minimal or no change in
UDVA.
71
These early results show reasonable effi cacy
but current safety is a concern as studies have reported
a loss of 2 lines of CDVA in 2.1%,
72
7%,
73
8%,
74
and
26% of eyes
75
as well as a loss of contrast sensitivity.
76
Further, it remains to be determined whether these mul-
tifocal ablation patterns are functionally reversible.
INTRASTROMAL KERATOMILEUSIS
Since femtosecond lasers were fi rst introduced into
refractive surgery, the ultimate goal has been to create
an intrastromal lenticule that can be removed manually
(refractive lenticule extraction [ReLEx]), thereby cir-
cumventing the need for an excimer laser. This was fi rst
described in 1996 using a picosecond laser to generate
an intrastromal lenticule that was removed manually af-
ter lifting the fl ap
77,78
; however, signifi cant manual dis-
section was required, leading to an irregular surface. The
switch to femtosecond laser improved the precision
79
and studies were performed in rabbit eyes in 1998
80
and
partially sighted eyes in 2003
81
; however, these initial
studies were not followed with further clinical trials.
Following the introduction of the VisuMax femto-
second laser in 2007,
82
the intrastromal lenticule method
was reintroduced in a procedure called femtosecond
lenticule extraction (FLEx). The 6-month results of
the fi rst 10 fully seeing eyes treated were published
in 2008
83
and results of a larger population have since
been reported.
84
The results were similar to LASIK ex-
cept for a slower visual recovery time, however, ad-
justments in energy settings and scan patterns have
improved the visual recovery time.
85,86
Intrastromal
lenticule procedures may have advantages over LASIK
as all of the potential variables associated with excimer
laser ablation are avoided, such as stromal hydration,
87
laser fl uence,
88,89
and other environmental factors.
90
Following the successful implementation of FLEx, a
new procedure called small-incision lenticule extrac-
tion (SMILE) was developed (Fig 5). This procedure
involves creating one or two small incisions through
which the lenticule interfaces can be separated, allow-
Figure 4. Slit-lamp photograph demonstrating intracorneal inlay (Flexivue
Microlens; Presbia Cooperatief UA, Amsterdam, The Netherlands)
implantation (arrow) in a pocket created with a femtosecond laser.
Figure 5. Retroillumination photograph of
the cornea of a left eye 1 day after small-
incision lenticular extraction. The 2.25-mm
small incision can be seen superotempo-
rally through which the refractive stromal
lenticule was extracted. The edge of the len-
ticule can also be clearly seen. The image
on the right shows a magnified view of the
area indicated by the yellow square. In this
magnified image, the edge of the cap—the
anterior interface of the lenticule—can also
be seen outside the edge of the lenticule.
918
Copyright © SLACK Incorporated
Femtosecond Laser Applications/Kymionis et al
ing the lenticule to be removed, thus eliminating the
need to create a fl ap. Therefore, this procedure will
only cut a small proportion of anterior corneal nerves
(only in the location of the incisions) meaning that
postoperative dry eye should be signifi cantly less than
that experienced after the creation of a fl ap or after
surface ablation. Another potential benefi t of SMILE is
increased biomechanical stability as the anterior stro-
mal lamellae, known to be the strongest region of the
stroma,
91
remain intact and therefore continue to con-
tribute to the corneal biomechanics. The results of the
rst prospective trials of SMILE have been reported
92,93
and now more than 50 surgeons routinely perform this
procedure worldwide. The VisuMax is currently the
only femtosecond laser being used for intrastromal
lenticular surgery.
CONCLUSIONS
Femtosecond laser technology has gained wide-
spread acceptance in the fi eld of corneal refractive
surgery due to its versatility, precision, and reproduc-
ibility. Femtosecond laser technology is now being
used successfully in performing various steps (capsu-
lorrhexis, clear corneal incisions, and phacolysis) of
cataract surgery precisely and reproducibly.
94
Addi-
tionally, femtosecond laser technology is utilized for
donor and recipient preparation in penetrating kerato-
plasty as well as lamellar keratoplasty.
95
Femtosecond
lasers hold great promise and will continue to provide
more applications in ophthalmic surgery, ultimately
contributing to the goal of emmetropia.
AUTHOR CONTRIBUTIONS
Study concept and design (G.D.K., D.Z.R.); data collection
(G.D.K., V.P.K., A.D.P.); analysis and interpretation of data (G.D.K.,
V.P.K., A.D.P.); drafting of the manuscript (G.D.K., V.P.K., A.D.P.,
D.Z.R.); critical revision of the manuscript (G.D.K., V.P.K., D.Z.R.);
supervision (G.D.K.)
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ERRATA
This article has been amended to include a factual correction. An error was identified subsequent to its original printing. On
page 753 of the article “Progression of Keratoconus and Efficacy of Corneal Collagen Cross-linking in Children and Ado-
lescents” by Chatzis and Hafezi, which was published in the November 2012 issue of the Journal of Refractive Surgery,
the title of the article should be “Progression of Keratoconus and Efficacy of Pediatric Corneal Collagen Cross-linking in
Children and Adolescents.This error was acknowledged on page XXX, volume 29, issue 1. The online article and its er-
ratum are considered the version of record.
This article has been amended to include a factual correction. An error was identified subsequent to its original printing. On
page 913 of the article “Femtosecond Laser Technology in Corneal Refractive Surgery: A Review” by Kymionis et al.,
which was published in the December 2012 issue of the Journal of Refractive Surgery, the Additional Procedures listed
for Zeiss VisuMax should be “FLEx, SMILE, ICRS, LK, PKP” instead of “FLEx, SMILE.” This error was acknowledged on
page XXX, volume 29, issue 1. The online article and its erratum are considered the version of record.
... e femtosecond (FS) laser is a type of neodymium laser with a near-infrared ray wavelength (1053 nm). It can focus with very short pulses of 1/10 15 of a second and make incisions by creating cavitation bubbles and a split interface during photodestruction of the corneal stroma [1,2]. e use of FS in ophthalmology began in the early part of the 21 st century and marked a new era in corneal refractive surgery. ...
... e use of FS in ophthalmology began in the early part of the 21 st century and marked a new era in corneal refractive surgery. It has been shown to create laser in situ keratomileusis (LASIK) flaps as well as or even better than mechanical microkeratomes (MMKs) [2][3][4]. FS-assisted LASIK (FS-LASIK) promises more predictable flaps and fewer flap complications, less ocular aberrations, better uncorrected visual acuity (UCVA), less variation in intraocular pressure, and less dry eye. However, complications, such as rainbowlike glare, haze, diffuse lamellar keratitis, and opaque bubble, cannot be ignored [2,[5][6][7][8]. ...
... FS-assisted LASIK (FS-LASIK) promises more predictable flaps and fewer flap complications, less ocular aberrations, better uncorrected visual acuity (UCVA), less variation in intraocular pressure, and less dry eye. However, complications, such as rainbowlike glare, haze, diffuse lamellar keratitis, and opaque bubble, cannot be ignored [2,[5][6][7][8]. ...
Article
Full-text available
Purpose: This study aimed to investigate whether femtosecond laser-assisted LASIK (FS-LASIK) surgery causes inflammation in the anterior chamber and to analyze its effect on endothelial cells. Methods: This prospective, longitudinal study included left eyes of 30 patients (19 females) who had undergone FS-LASIK surgery due to myopia and myopic astigmatism. Endothelial cell density (ECD) and morphological measurements were performed using a specular microscopy, and laser flare photometry was used to measure the anterior chamber flare values on the day of surgery. iFS™ Advanced FS and VISX STAR S4-IR Wavescan Excimer Laser platforms were used. Flare measurements were repeated on the postoperative 1st day and 7th day and the 1st and 3rd months. The endothelial measurements were repeated in the 3rd month. Results: Preoperatively, the mean flare was 5.59 ± 1.24 photons/ms; it was 6.49 ± 2.42 on the postoperative 1st day, 5.87 ± 2.27 on the 7th day, 5.68 ± 1.66 on the 1st month, and 5.35 ± 1.24 on the 3rd month. A significant difference was observed only between the preoperative and postoperative 1st day flare values (p=0.047). The decrease in the ECD was clinically insignificant but statistically significant, with an average of 97.0 ± 209.9 cell count/mm2 (3.3%, p=0.017). However, there was no significant change in the coefficient of variation (p=0.448) and hexagonality (p=0.096). No significant correlation was found between the increase in the flare value on the postoperative 1st day and variables. A significant correlation was found between the decrease in ECD and the preoperative ECD (r = 0.356, p=0.027). Conclusion: FS-LASIK caused minimal inflammation in the anterior chamber on only the 1st postoperative day; additionally, a minimal decrease of cell count with no morphological changes were noted in the endothelial cells on postoperative 3rd month. This trial is registered with NCT04899258.
... Снижение длительности импульса при использовании быстрого режима работы лазера за счет увеличения энергии и размера пятна позволяет уменьшить время лазерного этапа, что, соответственно, сводит к минимуму сопутствующее повреждение и воспаление тканей. Более того, световые импульсы с длиной волны 1043 нм не поглощаются роговицей и тепловое воздействие на роговицу минимально [21,22]. ...
... Полученные в ходе нашего исследования данные показали значительное снижение прозрачности роговицы в обеих группах на 1-е сутки в передних слоях на 21% в группе I и на 8,8% в группе II и 20 и 8,8% в средних слоях соответственно, со статистически достоверным превышением обратного светорассеивания после операции SMILE на 1-е и 5-е сутки послеоперационного периода. Снижение прозрачности роговицы после SMILE, скорее всего, можно объяснить активными процессами ремоделирования интерфейса на уровне примерно 120 мкм, которые могут быть связаны [22,25] с оставшимися обломками коллагеновых фибрилл и клеточных компонентов внутри кармана [26], что на ОКТ-сканах, обработанных с помощью программы ImageJ, можно визуализировать в виде микрополостей (лакун) между роговичным клапаном и стромой роговицы (рис. 2,3). ...
Article
Relevance. The study of the mechanisms of insufficiently rapid achievement of high visual acuity in the early postoperative period in the correction of myopia by the SMILE method is relevant. Purpose. To evaluate changes in corneal densitometry parameters after SMILE and FS-LASIK surgery in patients with moderate myopia. Material and methods. A study of 152 patients with moderate myopia was conducted, 68 were operated by SMILE and 84 – FS-LASIK. All procedures were performed using a VisuMax femtosecond laser and a MEL 80 excimer laser (Carl Zeiss Meditec, Germany). Assessment of visual acuity, corneal structure (OCT, Optovue, USA), corneal densitometry (Pentacam Scheimpflug, Germany) were performed before the operation, on the 1st, 5th day, 3, 6, 12 months after the operation. OCT scans were analyzed using the ImageJ program. Results. Оn the 1st day after SMILE, visual acuity (p=0.01) and transparency of the anterior and middle layers of the cornea were reduced than after FS-LASIK in the zone from 0 to 2 mm (p=0.045, p=0.001), from 2 to 6 mm (both p=0.001). These differences became statistically insignificant 5 days after surgery. By three and six months in the FS-ERASER group, the corneal transparency in the middle layers were reduced in the 0–2 mm and 2–6 mm zones (p=0.0001, p=0.001). In both groups, by 12 months, the corneal backscattering reached the values of the preoperative period (p>0,05). Conclusion. Refractive operations SMILE and FS-LASIK are accompanied by a decrease in corneal transparency, which is restored to preoperative values by 12 months. In the early postoperative period, an increase in densitometry indicators and a slower recovery of visual acuity after SMILE surgery may be due to active remodeling of the interface, which includes fragments of collagen fibrils and cellular components inside the intrastromal space. Key words: SMILE, FS-LASIK, densitometry, myopia
... Кераторефракционная хирургия (КРХ) -современный, динамически развивающийся сегмент офтальмологии, обеспечивающий высокопредсказуемый, безопасный и стабильный рефракционный результат у пациентов с широчайшим спектром аметропий [1]. КРХ, как правило, выбирается пациентами, ведущими активный образ жизни и нуждающимися в быстрой медико-социальной реабилитации, людьми с высокими требованиями к качеству жизни и демонстрирующими повышенные ожидания к результату коррекции [2,3]. ...
Article
Relevance . Corneal refractive surgery is a modern, dynamically developing segment of ophthalmology that provides highly predictable, safe and stable refractive results in patients with a wide range of ametropias. Corneal refractive surgery, usually is chosen by patients who lead an active lifestyle and need rapid medical and social rehabilitation, people with high requirements for the quality of life and showing increased expectations for the result of correction. Perhaps this is due to the fact that, according to a survey at the exit of the Department of refractive laser Surgery of the S.N. Fyodorov Eye Microsurgery Federal State Institution of the Russian Ministry of Health, Moscow, conducted after consulting a surgeon with a description of the course of the operation and the postoperative course, about 1 % of patients refuse surgery, fearing painful sensations in the postoperative period, and 23.4 % of the expected postoperative discomfort causes strong concerns. Purpose . To study the clinical efficacy and safety of Broxinac (0.09 % bromfenac solution) in the early postoperative period of corneal refractive surgery. Materials and methods . The study included 168 patients (168 eyes) with moderate and high myopia after PRK (24 eyes), FemtoLASIK (78 eyes) and ReLEx SMILE (66 eyes), divided into equal subgroups: in the main group, Broxinac was instilled once 30 minutes after the operation, and in the control group — placebo. In the PRK subgroup of the main group, daily instillations of Broxinac were continued until complete reepithelization. The severity of the indicators “eye pain”, “photophobia”, “lacrimation”, “foreign body sensation” was evaluated on a five-point scale, the state of the corneal epithelium when stained with fluorescein, and overall satisfaction with the operation. Results and discussion . It is established that the analgesic effect occurred on average after 4.4 ± 0.6 minutes. Broxinac had a rapid, pronounced analgesic effect in patients in the early postoperative period after keratorefractive surgery, without slowing of corneal reepithelization, and can be recommended for use in clinical practice for analgesia and relief of aseptic inflammatory reaction in the early postoperative period after FemtoLASIK and PRK. The ReLEx SMILE does not require pain relief. Conclusion . Analgesia of the early postoperative period increases patient satisfaction with the result of the operation, popularizes it and helps to attract patients who previously refused surgical correction of ametropia due to fear of painful sensations.
... [2] Femtosecond laser (FS) technology development has improved the outcomes of several corneal surgeries. [3] When applied to the cornea, the FS pulse leads to the formation of cavitation bubbles that hastens customized corneal dissection for PK, [4][5][6] deep anterior lamellar keratoplasty, [7] intrastromal corneal ring segments, [8] and small microincisional lenticular extraction. [9] In PK, FS laser-assisted keratoplasty (FAK) has been reported to have many advantages over conventional mechanical trephination. ...
Article
Purpose: To describe and compare the histological changes in the cut edges of the remaining donor corneal rim using femtosecond laser-assisted keratoplasty (FAK) versus conventional penetrating keratoplasty (PK) via light and transmission electron microscopic examination. Methods: This was a prospective observational study of 10 eyes; 5 FAK (top-hat technique) and 5 conventional PK. Main outcomes were histological findings at the cut edge of the donor corneal rim (at 3, 6, 9, and 12 o'clock). Results: Cellular and ultra-cellular changes in the form of stromal edema, disorganized collagen fibers, and nuclear changes were more prominent in the FAK eyes as compared to the conventional PK ones. Conclusion: FAK induces more collateral damage in the cut edge of corneal donor graft at cellular and ultra-cellular levels, compared to conventional trephination. Further studies are required to investigate the clinical ramifications of this observation.
... Breakthroughs in sub-picosecond (ps) pulsed lasers [1] have opened new horizons in fundamental and applied physics, allowing new phenomena observation and innovative optical technology [2][3][4][5][6] development. In fact, by using the probe based on femtosecond-nanosecond (fs-ns) time scale regimes, it is possible to reconstruct the basic mechanisms of the absorption/luminescence photocycle occurring on fs-ps time scales in different studied systems [7][8][9]. ...
Article
Background. In the available literature, there are isolated publications devoted to the topic of the possible effect of laser correction by the Femto LASIK method on the myopic eye choroid. In this connection, in our opinion, the relevance of continuing research in this direction remains. The aim of this study was to examine the volume of the retina in the macular zone, the thickness of the choroid and the ciliary body using optical coherence tomography on myopic eyes after femtosecond-assisted laser in situ keratomileusis in the short term. Material and methods. 30 patients (30 right eyes) aged 20 to 35 years, suffering from mild and moderate myopia, but without pathological changes in the retina according to OCT, made up the study group. All patients underwent myopia correction using the Femto LASIK method. Before the operation, after 4 hours and the next day, they underwent the examination of the retinal volume in the macular zone, the choroidal and the ciliary body thickness using OCT Results. The analysis of the obtained results of the studied parameters showed that the ciliary body thickness and the retinal volume in the macular zone did not undergo statistically signifi cant changes and remained within the preoperative values (p > 0.05). We observed a tendency to an increase in the thickness of the choroid 4 hours after the operation, but the carried out statistical analysis did not confi rm the reliability of its changes (p > 0.05). On the next day, the choroidal thickness indices practically recovered to the preoperative level (p > 0.05). Conclusion. A study of the retinal volume in the macular zone, the thickness of the choroid and ciliary body using OCT in myopic eyes in the short term after Femto LASIK showed the absence of statistically signifi cant changes in the studied parameters, which indirectly indicates the safety of this method of laser correction for the posterior segment of the eye.
Chapter
The idea of reshaping corneal morphology based on intrastromal lenticule implants started since the introduction of Femtosecond Laser (FSL) in corneal surgery. Stromal Lanticule Addition Keratoplasty (SLAK) is an evolving minimally invasive procedure of donor corneal lenticules implantation through recipient intrastromal pocket, inducing central corneal flattening while increasing the stromal thickness in advanced corneal ectasia, adding stromal tissue with beneficial biomechanical effects, thus reducing the need of traditional corneal transplant.
Chapter
CXL can be efficaciously performed outside of the Operating Rooms (ORs), ideally at the slit lamp. This approach could take numerous advantages, as it lowers costs and brings CXL technology away from ORs. This chapter discusses how CXL technology can be safely incorporated into the medical office, respecting indications, in remote areas where an OR is not available or in large centers where the efficiency and costs can be optimized.
Article
A method to determine the optimum laser parameters for maximizing laser induced refractive index change (LIRIC) while avoiding exceeding the damage threshold for different materials with high water content (in particular, polymers such as hydrogels or the human cornea) is proposed. The model is based upon two previous independent models for LIRIC and for laser induced optical breakdown (LIOB) threshold combined in a simple manner. This work provides qualitative and quantitative estimates for the parameters leading to a maximum LIRIC effect below the threshold of LIOB.
Conference Paper
PURPOSE: To determine the efficacy of INTACS insertion using a femtosecond laser in, the treatment of keratoconus and to compare it to the technique using a mechanical spreader. METHODS: INTACS we re inserted in 10 eyes using the mechanical spreader to create the channels and subsequently on another 20 eyes using the femtosecond laser. Uncorrected (UCVA) and best spectacle-corrected visual acuity (BSCVA), manifest refraction, and corneal topography were, measured prior to surgery, at 6 months (femtosecond group ) and 1 year (mechanical group). Pre- and postoperative data were analyzed to determine changes in the above parameters. RESULTS: Both groups showed significant reduction in average keratometry (K), spherical equivalent refraction, BSCVA, UCVA,:surface regularity index (SRI), and surface asymmetry index (SAI). The laser group performed better in all parameters except change in SRI. Results of the laser versus- the mechanical spreader were as follows: reduction in spherical I equivalent refraction (3.98 vs 2.96), change in average K (2.91 vs 2.52), improvement in UCVA (4.13 vs 3.63), improvement in BSCVA (3.92 vs 1.63), change in SRI (0.37 vs 0.64), and change in SAI(1.00 vs 0.70). Statistical analysis, however, did not reveal any statistically significant differences between the two groups or any single parameter studied. The biggest improvement in the laser group versus the mechanical group was BSCVA (P = .09). Overall success, defined as contact lens or spectacles tolerance, was 85% in the laser group and 70% in the mechanical group. CONCLUSIONS: Inserting INTACS using the femtosecond laser to create the channels is as effective as using the mechanical spreader.
Article
• We produced corneal excisions with nanosecond (ns)-, picosecond-, and femtosecond (fs)-pulsed lasers at visible wavelengths. The threshold energy for ablation was proportional to the square root of the pulse duration and varied from 2.5 microjoules (μJ) at 100 fs to 500 μJ at 8 ns. Excisions made with picosecond and femtosecond lasers were ultrastructurally superior to those made with nanosecond lasers and, at pulse energies near threshold, showed almost as little tissue damage as excisions made with excimer lasers at 193 nm. We conclude that ultra-short-pulsed lasers at visible and near-infrared wavelengths are a possible alternative to excimer lasers for corneal surgery and might have advantages over conventional ophthalmic neodymium-YAG lasers for some intraocular applications.
Article
We describe a new system for performing transverse arcuate corneal incisions for the correction of astigmatism. The instrument consists of a conical housing with suction and/or friction fixation to the limbus and two micrometric diamond knives mounted on a carrier that can be rotated by a gear mechanism. The depth, length, and location of the incisions can be predetermined. Light microscopy of donor eye corneas documented the achieved incision depth. One sweep at normal speed produced an incision depth 28% less deep than the preset depth. One sweep at low speed achieved depths of approximately 100% of the knife setting. Variability from one incision to another in the same cornea was related to blade sharpness. We report successful use of the instrument in five consecutive eyes with naturally occurring astigmatism.
Article
Purpose: To investigate the correction of post-penetrating keratoplasty (PKP) astigmatism using laser in situ keratomileusis (LASIK). Visual and refractive outcomes were evaluated after LASIK was performed in 1 step (lamellar cut and ablation in 1 procedure) or 2 steps (lamellar cut then ablation in 2 successive procedures).
Article
To evaluate the changes in corneal collagen architecture subjected to different laser-firing patterns during refractive lenticule extraction. Singapore Eye Research Institute, Singapore. Experimental study. Refractive lenticule extraction was performed in rabbits without lenticule removal. Rabbits were divided into 4 groups that had incisions in the following firing patterns: (A) from periphery in (lenticule's posterior surface) and from center out (lenticule's anterior surface); (B) from center out and from center out; (C) from periphery in and from periphery in; and (D) from center out and from periphery in. The corneas were collected 18 hours postoperatively and were subjected to immunofluorescent staining of fibronectin, CD11b, and collagen type I. Ultrastructural analysis was performed using transmission electron microscopy (TEM). Refractive lenticule extraction-treated corneas showed no significant difference in fibronectin and CD11b expression. Similar expression patterns of collagen type I were observed in corneas that had femtosecond firing patterns A, B, and C; however, a discontinuous and relatively more intense staining pattern along the anterior plane of the lenticule was detected in corneas treated with pattern D. The TEM also showed a more disrupted collagen arrangement along the anterior incision site in pattern D-treated corneas. Differential laser firing patterns during refractive lenticule extraction resulted in different levels of collagen derangement along the anterior plane of the lenticule, with pattern D showing the most disrupted surface. Such disruption in the collagen architecture might affect postoperative visual recovery and refractive outcomes. No author has a financial or proprietary interest in any material or method mentioned.
Article
To compare intraocular lens (IOL) power calculation and refractive outcome between patients who underwent laser refractive cataract surgery with a femtosecond laser and those with conventional cataract surgery. In this prospective study, 77 eyes from 77 patients underwent laser refractive cataract surgery (laser group; Alcon LenSx femtosecond laser), and conventional cataract surgery with phacoemulsification was performed in 57 eyes from 57 patients (conventional group). Biometry was done with optical low coherence reflectometry (Lenstar LS900, Haag-Streit AG), and IOL calculation was performed with third-generation IOL formulas (SRK/T, Hoffer Q, and Holladay). The refractive outcome was analyzed using the mean absolute error (MAE; difference between predicted and achieved postoperative spherical equivalent refraction), and multivariable regression analysis was performed to compare the two groups. No significant differences were found between age, axial length, keratometry, and preoperative corrected visual acuity in the laser and conventional groups (P>.05; Mann-Whitney U test). At least 6 weeks after surgery, MAE was significantly lower in the laser group (0.38±0.28 diopters [D]) than in the conventional group (0.50±0.38 D) (P=.04). The difference was the greatest in short (axial length <22.0 mm, 0.43±0.41 vs 0.63±0.48) and long (axial length >26.0 mm, 0.33±0.24 vs 0.63±0.42) eyes. Laser refractive cataract surgery with a femtosecond laser resulted in a significantly better predictability of IOL power calculation than conventional phacoemulsification surgery. This difference is possibly due to a more precise capsulorrhexis, resulting in a more stable IOL position.
Article
The aim of this study was to examine the mesopic contrast sensitivity (CS) and glare sensitivity following intrastromal femtosecond laser correction of presbyopia (INTRACOR). In this study 25 patients with slight hyperopia and presbyopia underwent femtosecond laser correction in the non-dominant eye. Mesotest II measurements (OCULUS Optikgeräte, Wetzlar, Germany) were performed with and without glare at each of four different contrast levels preoperatively as well as 3, 6, 12, 18 and 24 months postoperatively. Data were compared using the Wilcoxon-test with a level of significance of p < 0.05. After 24 months the median CS decreased from 1:2 to 1:2.7 without glare and from 1:23 to 0 with glare. Of all patients 36% showed loss in CS without and 52% with glare and CS did not show any statistically significant differences between the treated and the untreated fellow eyes after 12 and 24 months. Overall 9 out of 18 monocular treated patients showed no binocular night driving ability according to the recommendations of the German Society of Ophthalmology (DOG) and the Professional Association of German Ophthalmologists (BVA) 24 months following INTRACOR. INTRACOR can lead to a slight reduction of mesopic contrast sensitivity and an increase of glare sensitivity. Possible consequences on night driving ability should be discussed with the patients prior to treatment.
Article
To analyze the results of LASIK retreatment performed by relifting the original femtosecond laser-created flap. A retrospective analysis was performed on 1298 eyes from 688 patients treated with LASIK using the femtosecond laser to identify 88 consecutive eyes of 71 patients that underwent attempted flap lift to treat residual refractive error. The eyes were separated in groups in which the flap lift was possible or flap lift was not possible to investigate factors that could make flap lifting more difficult. The main factors evaluated were bed and side-cut energy and time between original surgery and retreatment. In addition, all retreated eyes were studied as a group to evaluate the refractive outcomes of flap lift retreatment. In 10 (11.3%) retreated eyes, flap lift was not possible without risk of flap injury due to strong healing of the original femtosecond laser interface. The group of eyes in which the flap could not be relifted had the attempted retreatment performed a longer time period after original LASIK (10.3±3.3 months) compared to the group in which the flap could be re-lifted (5.24±3.14 months) (P<.001). No significant differences were found between groups in any other parameters, including bed and side-cut energies. After retreatment, 82% of eyes achieved 20/20 or better uncorrected visual acuity. This study provides clinical evidence that flap lift retreatment after femtosecond laser-assisted LASIK achieves excellent clinical results and is significantly easier to perform in the first 6 to 8 months after primary LASIK.