femtosecond laser in ophthalmology by Dr. Hind Safwat (Al Azhr university)
Hind M. Safwat Al Shwadfy
T A ophthalmology (Al zhraa university hospital)
Assist. Prof./ Mona Farag
(ophthalmology department-Al Azhar University)
Introduction about femtosecond laser
Femtosecond laser in the ophthalmic diagnostic tools
Femtosecond laser in the corneal and refractive
Femtosecond laser in the cataract surgery
Femtosecond laser in the glaucoma surgery
Femtosecond laser in the photodynamic therapy.
The development of the ruby laser almost a half century ago
by Maiman opened up wide new vistas in ophthalmology,
resulting in a flood of practical clinical applications of lasers
in eye surgery.
The development of clinical argon, krypton, carbon dioxide,
neodymium-doped yttrium aluminum garnet (Nd:YAG), and
excimer laser systems in ophthalmology made it possible to
treat a wide eye diseases and disorders.
Remember, the optically transparent refractive
layers of the eye, such as the cornea and lens, do
not absorb electromagnetic radiation in the visible
or near-infrared spectrum at low power densities,
allowing light to pass through without alteration of
However, At higher power densities; these
structures do absorb the light energy, leading to
plasma generation and tissue disruption.
The first practical use of near-infrared lasers in
clinical ophthalmology was the focused Nd:YAG
The Nd:YAG laser has a pulse duration in the
nanosecond (10ˉ9 second) range and produces
photodisruption (photoionizing, or optical break
The zone of collateral tissue damage with the
nanosecond Nd:YAG laser may easily exceed 100
µm (a problem !!).
By shortening the pulse duration of the near
infrared laser from the nanosecond to the
picosecond (10 ˉ 12 second) domain and then to
the femtosecond (10 ˉ 15 second) domain, the
zone of collateral tissue damage is progressively
reduced (1 µm).
FSL is a focused infrared laser with a wavelength
of 1053 nm that uses ultrafast pulses with a
duration of 100 fs.
Ultra fast, high energy, and broad waveband
width, and long wave length (which can be
It is a solid-state Nd:Glass laser (generated from
It can be doubled and tripled to be focused to
near structures as cornea.
It’s non visible, but can be combined with helium
gas to be visible.
The technology of the FSL was first introduced in
the labs in 1990 but commercially in late 2001,
and technological evolution has resulted in a
gradual increase in its higher laser firing
frequency, which recently reached 500 kHz from
its original 6 kHz.
The higher laser frequency permits lower energy
per pulse and tighter line separation.
Mecanism of action
FSL energy is absorbed by the
tissue, resulting in plasma
This plasma of free electrons and
ionized molecules rapidly expands,
creating cavitation bubbles.
The force of the cavitation bubble
creation separates the tissue.
FSL in the diagnostic
Ultra high resolution OCT
Second harmonic–generation (SHG)
Ultra High Resolution OCT
(UHR - OCT)
The axial resolution of OCT depends on the bandwidth of
light source used for imaging.
Compact super luminescent diodes (SLDs) have been
extremely used in OCT systems.
SLDs in ophthalmic OCT are near infrared with wave length
near 800 nm., and bandwidth of 20 to 30 nm. that give axial
resolutions 8 – 10 µm.
Multiplexing SLDs at different wavelengths
around 850 nm. Can achieve bandwidth 150
nm. With axial resolution ~ 3 - 5 µm.
FSL which produced from Ti : Sapphire can
produce light source for UHR-OCT with multiple
wave lengths (800, 1000 & 1300 nm.) with
bandwidth ~ 260 nm. Achieving axial resolution
~ 1 - 3 µm.
Development of nonlinear optical (NLO) imaging
techniques such as second harmonic–generated (SHG)
imaging has emerged as a powerful new tool for
investigating collagen organization.
Briefly, during SHG the extremely high field strengths
associated with ultra short laser pulses cause an oscillating
polarization in certain molecules, such as collagen, that
results in the emission of light at exactly half the
wavelength of the laser beam.
o Finally, because of the high axial & lateral resolutions and the increased
penetration depth of infrared light, it allows for 3-D image acquisition through
the full thickness of the cornea.
o Using this imaging paradigm, SHG studies showed that collagen is arranged
in a more complex fashion than previously thought.
FSL in the Corneal
& Refractive Surgery
Born of a Workplace Accident :
“The medical use of the FSL at the University of Michigan: A
graduate student in the ultrafast lasers lab had sustained a
well-defined laser burn on his retina. The examination of
this burn by a second-year resident [Ron M. Kurtz, MD]
led to collaborative research between the department of
ophthalmology and the school of engineering, and
ultimately to the original femtosecond medical laser,
marketed as (with FDA approval) IntraLase in 2001.”
Why FSL in the refractive & corneal
1) Ultra-short pulse duration (10 ˉ 15 sec.) has the ability
to deliver laser energy with minimal collateral
damage to the adjacent tissue (1µm).
2) It can be
within or behind
3) It is capable, to a certain extent, of passing
through optically hazy media, such as an
4) The laser may be applied in multiple
geometric patterns including vertical, spiral,
or zig-zag cuts.
FSL systems used in the corneal and
1st released commercial device was: Intralase FS™
(Abbott Medical Optics, Abbott Park, Illinois);
Femtec® (20/10 Perfect Vision, Heidelberg, Germany);
VisuMax Femtosecond System® (Carl Zeiss Meditec,
Femto LDV™ (Ziemer Group, Port, Switzerland); and
Wavelight FS200® (Alcon, Fort Worth, Texas).
The suction ring is centered over the pupil.
The docking procedure is then initiated while keeping the
suction ring parallel to the eye.
An applanating glass contact lens is used to stabilize the
globe and to flatten the cornea.
The surgeon administers the FS laser treatment. Each pulse
of the laser generates microscopic gas bubbles dissipating
into surrounding tissue.
Multiple pulses are applied next to each other to create a
cleavage plane and ultimately the LASIK flap.
Suction is then released.
A spatula is carefully passed across the flap starting at the hinge
and sweeping inferiorly to lift the flap for excimer laser ablation.
1. Reduced incidence of flap complications like
buttonholes, free caps, irregular cuts etc.
2. Control over flap diameter and thickness, side cut
angle, hinge position and length.
3. Increased precision with improved flap safety and
better thickness predictability.
4. Capability of cutting thinner
flaps to accommodate thin
corneas and high refractive
5. Stronger flap adherence.
6. Better contrast sensitivity.
7. Decreased incidence of epithelial ingrowth.
8. Less increase in IOP required.
9. Lesser incidence of dry eye.
10. Lesser hemorrhage from limbal vessels.
11. The ability to retreat immediately if there is
incomplete FS laser ablation.
1. Opaque bubble layer (OBL): Gas bubbles routinely
accumulate in the flap interface during FSL treatment,
but occasionally they may dissect into the deep stromal
bed(obscuring excimer laser tracker), reaching AC, or
escape to subepithelial (resulting in button hole).
2. Transient light sensitivity syndrome (TLSS):
Also called as good acuity plus photosensitivity (GAPP).
Occurs days to weeks after FS - LASIK.
Patients present with extreme photophobia and good
visual acuity with paucity of clinical findings on exam.
It resolves without sequel but requires aggressive
topical steroids for weeks. Proposed mechanism is
either an inflammatory response of the surrounding
tissue to the gas bubbles or biochemical response of
the keratocytes to the near-infrared laser energy.
3. Micro-irregularities on the back surface of the FSL
LASIK flap can cause “rainbow glare”
4. Photodisruption-induced microscopic tissue injury
and ocular surface inflammatory mediators may
cause lamellar keratitis in the flap interface.
5. Increased difficulty in lifting the flap if retreatment is
required after that (because of good adherence).
6. Increased cost.
7. Moving the patient between 2 laser instruments.
Femtosecond lenticule extraction (FLEx)
& Small-incision lenticule extraction
Femtosecond-only vision correction is now available for
myopia under Carl Zeiss Meditec’s ReLEx umbrella,
which comprises both femtosecond lamellar extraction
(FLEx) and small-incision lamellar extraction (SMILE).
Using a curved applanation plate, the Zeiss VisuMax
precisely cuts and removes a lenticule, rather than
FSL in penetrating keratoplasty
Penetrating keratoplasty (PKP) was under evolution from
manual blade → trephination → laser assisted.
(FLEK) is femtosecond laser-enabled keratoplasty.
1- Cuts are at a precise depth which is consistent
and reproducible with limited damage to surrounding
2- Wound configurations create more surface area
for healing, improve tissue alignment and
distribution, require less suture tension for
alignment of tissue, and have superior
biomechanical strength, rapid visual recovery and
II. Specific; according to type of cuts (see later).
Disadvandages (or contra indication):
* Absolute: any condition preventing proper laser
docking such as severe ocular surface irregularity,
elevated glaucoma filtering bleb or glaucoma shunt
implant, small orbits, extremely narrow palpebral
fissures, and recent corneal perforations.
* Relative: prior PKP or globe trauma because of the
risk of corneal/globe rupture and expulsive
hemorrhage(controverse), severe peripheral corneal
Types of FSL cuts in PKP
Standard ''butt-joint” in
Top – hat:
The first FSL customized trephination pattern used.
This cut possesses the advantages of improved
wound seal (7 folds less leak),and stability due to its
Replacement of a greater amount of endothelial
cells that may be beneficial in endothelial diseases
such as Fuchs' dystrophy.
The "top-hat" incision suture placement can vary as
precision is required to pass the suture through the posterior
wing, leading to the possibility of tissue misalignment and
posterior wound gape that may impact refractive outcomes.
The larger posterior corneal diameter of the "top-hat"
configuration brings the donor tissue closer to the angle, and
could theoretically increase the risk of endothelial rejection
Provide greater anterior stromal replacement and
therefore may be more advantageous in diseases such
as keratoconus or pathologies involving primarily the
Less topographic astigmatism, and time to complete
suture removal outcomes.
A water-tight seal of the graft-host interface was
easier to achieve in the "top-hat" profile compared
with the "mushroom”, due to the contribution of the
force of the IOP on the inner lamella of the "top-hat"
cut graft, pressing it against the host cornea.
Ring-shaped microcystic edema over the interface of
the graft-host overlap zone and protrusion of the
anterior lamella between sutures associated with
ointment deposits and bacterial infiltrates.
Zig – zag:
Its angled anterior side cut creates a precise donor-
host transition with less potential for tissue
misalignment and overall optical distortion.
The greater surface area of donor-host contact
allows for improved seal of the incision site,
improved tensile strength of the wound, and faster
The "zig-zag" configuration has the simplest
learning curve for suturing (inner side of Z, 50 %
of depth, and regular tensile strength).
FSL in the deep anterior lamellar
The use of the FSL in DALK was first described by Drs
Farid and Price in 2009 using the "zig-zag" incision
Better donor-host fit, increased surface area, faster
wound healing promoting earlier suture removal, and
reduced astigmatism, resulting in overall increased
success of the procedure.
In addition, FS-assisted DALK is technically easier to
perform compared with manual DALK.
Customized FS trephinations (zig-zag or mushroom)
create a posterior cut whose depth is about 50 to 100
μm from the endothelium, allowing the needle or a
blunt cannula to be passed easily and more accurately
just anterior to Descemet membrane and thereby
facilitating a successful big-bubble dissection.
FSL in anterior lamellar
Yoo et al described a sutureless technique for
FS-assisted ALK (FALK) to create smooth
lamellar dissections just deep to the corneal
smoother stromal bed.
FSL in Descemet stripping assisted
endothelial keratoplasty (DSAEK)
Still under trials with doubt in its result.
Interface haze resulting from the roughened
collagen fibrils produced by the FSL.
High rates of graft dislocation and loss of
endothelial cells when the FSL was used to
prepare the endothelial graft tissue.
FSL in Astigmatic Keratotmy
AK is the most commonly used method for the reduction of high
amounts of astigmatism in postoperative PK patients.
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 fibrotic ring formed as part of the healing 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 difficulties (especially in non
unpredictability, and complications
such as wound dehiscence, epithelial
abrasions, and perforation.
Compared with the mechanical
method, the use of FSL offers the
advantages of higher precision and
stability as well as more accurate
planning of the length, depth, and
optical zone of the cuts.
FSL in Intrastromal corneal ring
Intrastromal corneal ring segments are implants originally designed
to correct low to moderate myopia. Currently, they are used to treat
postoperative LASIK corneal ectasia, pellucid marginal
degeneration, and keratoconus.
Intrastromal corneal ring segments are inserted in intrastromal
channels (created either manually or using 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 flattening of the central cornea.
Compared to the manual technique, FSL makes
tunnel creation faster, easier, and more reproducible
and offers accurate tunnel dimensions (width,
diameter, and depth).
But, with mechanical dissectors, segment depth may
be shallower at positions further from the incision but
depth is consistent throughout when using FSL.
Intraoperative incomplete channel creation
Postoperative segment migration (1.3%)
Intraoperative adverse events such as endothelial
perforation (0.6%), and vacuum loss (0.1%).
Postoperative complications such as superficial
movement of the segments (0.1%), corneal
melting (0.2%), and infection (0.1%).
FSL in cross linking
Traditionally, riboflavin is applied to a debrided cornea (epith.
off), followed by ultraviolet exposure for 30 minutes.
An innovative approach to this procedure using FSL spares
the epithelium, thus reducing post-treatment pain and
providing a more rapid visual rehabilitation.
Intrastromal pockets can be created with FSL, which then
allows for the direct injection of riboflavin with subsequent
FSL in prespyopia
INTRCOR (intrastromal correction of
presbyopia with femtosecond laser)
It depends on monovision idea for
correction of prespyopia.
The surgeon uses the laser to create
five concentric rings of different
depths, centered on the pupil, in the
cornea of the patient’s non-dominant
eye. The inner ring is approximately
0.9 mm in diameter and the outer
ring is 3.2 mm.
FSL lentotomy may offer a viable new approach to treating
The basis for this treatment relates to the idea that nuclear
sclerosis is the main contributor to presbyopia. Therefore, a
cure for improving near vision function would be to increase
the flexibility of the nucleus of the crystalline lens.
FSL lentotomy involves creation of intra lenticular incisions to
result in additional gliding planes within the lens substance,
thereby increasing its flexibility.
The results of ex vivo studies
show that with use of
appropriately selected cutting
parameters, an increase in
flexibility of up to 73 % can be
achieved in human globes.
The FSL was chosen for this
technique since its ultrashort
pulse profile allows for
precision cutting within the
lens without causing damage
to the surface.
FSL in corneal inlays
FSL may be used to create intrastromal pockets
for insertion of biocompatible corneal inlays for ttt of
Corneal inlays are disc shaped corneal implants
work by changing the refractive index of the cornea.
The central zone of the implant is neutral or plano,
and has no refractive power. It allows light rays from
distant source to focus on the retina, preserving
The central neutral zone is surrounded by
one circular zone of additional positive
power, which focus light rays from near
objects on the retina, and improve near
vision (their design is similar to multifocal
contact lens or intraocular lens).
1- Hydrogel; as Presbylens & Flxivue microlens.
2- Non Hydrogel AutoFocus Kamara inlay
Slit-lamp photograph (left) & Retro illumination appearance of intracorneal inlay
(Flexivue Microlens; Presbia Cooperatief UA, Amsterdam, The Netherlands)
implantation (arrow) in a pocket created with a femtosecond laser.
FSL assisted biopsy (FAB)
Corneal biopsy consists of an option adopted in
patients in which corneal scraping does not provide a
Until recently, corneal biopsies have been performed
manually using diamond knifes, beaver blades or
Among the disadvantages of the manual technique
are imprecision of incision depth, inadequate tissue
removal, corneal scarring and perforation.
The introduction of FSL technology in
ophthalmology has provided surgeons with the
ability to perform biopsies in a safer and more
The predictability of cutting with the FS in
predetermining depth without scarring and
inducing irregular astigmatism are the main
benefits that encourage the use of FSL.
FSL in the Cataract Surgery
FDA-approval for FSL assisted cataract surgery was in 2010
for cataract surgery.
There are the most common laser plateforms in the cat. surgery;
1- OptiMedica Catalys (Santa Clara, CA) >>> is currently seeking FDA
approval and is already available outside of the United States.
2- LenSx (recently acquired by Alcon, Fort Worth, TX) >>> approved for
lens fragmentation, anterior capsulotomy, and corneal incisions.
3- LensAR (Winter Park, FL) >>> recently received FDA approval for lens
fragmentation and anterior capsulotomy.
Any patient with cataract either associated with astigmatism or other
refractive errors or not !
However, it’s also contraindicated in:
1. Patients who have deep set orbits or those with tremors or
dementia may do poorly with the initial docking of the lens that
requires patient cooperation.
2. Anterior basement membrane dystrophy, corneal opacities (such
as arcus senilis, corneal dystrophies, and trauma- or contact lens-
induced scars), ocular surface disease, pannus with encroaching
blood vessels, or recurrent epithelial erosion syndrome.
3. Additionally, the level of increase in IOP induced
by the docking may be a significant
contraindication for patients with glaucoma, optic
neuropathies, or borderline endothelial pathology.
4. Diabetics may have undiagnosed epithelial
5. Patients with poor dilation.
6. Relative contraindication in dense PSC with
vacoules (interrupt proper posterior capsule
Pupillary dilatation and topical anesthesia.
Applanation of the cornea with a docking system
(OptiMedica platform has a liquid optics interface
which increases IOP only by 15 mmHg).
Anterior segment imaging is then performed.
LenSx and OptiMedica utilize (FD-OCT), while
LensAR utilizes Scheimpflug imaging technology.
This step is required to find anatomical
landmarks(especially iris & posterior capsule) for
laser pattern mapping.
Preprogrammed corneal incisions for temporal wound,
paracentesis, and any optional limbal-relaxing incisions (LRIs)
can be adjusted at this point.
N B; If a corneal incision is created, not open until the patient is moved to the operating room
(fear of infection).
The pattern is then centered and the laser is activated. Laser-
assisted capsulotomy is performed, followed by lens
N B; This sequence is justified (not as LensAR) because lens fragmentation causes release
of gas bubbles, which can distort the anatomy and affect capsulotomy planning.
Now, Patient then undergo removal of the anterior
capsulotomy, followed by standard phacoemulsification.
1. FSL performs corneal incisions allowing for more square
architecture, which has proven more resistant to leakage.
2. FSL systems can also create LRIs to treat astigmatism.
Since the FSL systems are capable of delivering cuts to
precise depths and lengths, these LRIs may be more
accurate and standardized compared to manual
3. Manual capsulorhexis is known to be the most technically
difficult part of cataract surgery for trainees, leads to tears.
So the smooth, regular edges by FSL may offer
superior capsular strength and resistance to
4. The FSL may be able to deliver a more circular, stronger,
precisely planned and executed capsulorhexis, which
could afford more control over capsulotomy
unpredictability (as in manual) and offer less PCO & more
accurate refractive outcomes.
5. With consideration to a reduction in ultrasound energy and
instrumentation during fragmentation, FSL may show
improved safety and decreased complications.
1. The high cost.
2. Moving the patient between 2 rooms(laser instrument
room to surgical microscope room), may increase(or
at least the same) post operative endophthalmitis
although the water tight squared CCI.
3. Limitations of FSL use in very high-grade
opacifications have not yet been delineated in
4. Diabetics may have persistent epithelial defects
from the trauma of docking.
5. Need a steady lens, so cannot be applied for
6. Laser mapping image cannot be done in cases of
poor dilatation as posterior synechiae,
intraoperative floppy iris syndrome suspects, or
those on chronic miotic medications.
7. Contra indications (see before).
FSL in the Glaucoma
Selective trabeculoplasty (still in vitro).
Guarded filtration surgery.
Minimal invasive glaucoma surgery (deep
FSL in selective trabeculoplasty
In 2005, Toyran et al used an FSL to perform
photodisruption of human trabecular meshwork(TM)
strips ex vivo.
Unlike the minimal disruption of tissue produced by
selective laser trabeculoplasty, FSL can make full-
thickness ablation channels through the TM.
Theoretically, these tracts could permit direct access of
aqueous humor from the anterior chamber to Schlemm
Histological evaluation of the tissue confirmed
the reliable creation of fistulous tracts without
1- FSL photodisruption is very specific with
2- In addition, a few small channels should be
more than enough to increase the outflow
facility to therapeutic levels.
FSL in guarded filtration surgery
The precision of scleral incisions created with the FSL has
great potential to standardize portions of guarded filtration
* Inherent light-scattering properties of the sclera, which could
lead to imprecise incisions and collateral damage.
* Although longer laser wavelengths (to 1.7 μm) might
overcome this problem, current hardware and software
platforms used in cataract surgery are not equipped for
FSL in minimal invasive glaucoma
Initial attempts at deep sclerectomy using the FSL
occurred in 2007.
Bahar et al used the IntraLase FSL to create both
superficial and deep partial-thickness scleral flaps in
human cadaveric eyes. After amputating the deep flap,
they observed aqueous percolating through the exposed
Further testing is required to optimize the laser settings,
and no human trials have been published to date.
FSL in the photodynamic
High peak power pulse energy by femtosecond
ultrashort pulse laser (titanium sapphire laser)
delivered at an 800 nm wavelength(after trippling
to be in ultraviolet region) for corneal
neovascularizatin mediated by indocyanine green
Application FSL - PDT in AMD and melanomas is
still under research.
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