Transcript UNIVERZITA KOMENSKČHO V BRATISLAVE LEKARSKA FAKULTA

Femtosecond lasers are lasers that emit light pulses, the duration of them are
in the femtosecond range. The spreading speed of these lasers travels within
one femtosecond ( 1fs= 10^15 s ).
Femtosecond lasers have been used successfully in ophthalmic surgery since
2001.
The technology has been applied widely most common know today in LASIK
(Laser in Situ Keratomileusis) refractive surgery. In Femtosecond lasers
technique the femtolasik laser replaces a mechanical device, microkeratome,
to create a precise corneal flap preparing the eye for the secondary laser
ablation in order to change the patient’s refractive error.
There are several benefits, Femtosecond lasers have been noted to be more
precise than microkeratomes, with fewer likely collateral tissue effects.
The femtosecond laser was first used clinically in cataract surgery by
professor Zoltan Nagy in Budapest in 2001.
The role of femtosecond lasers cataract surgery is to assist or replace several
aspects of the manual small incision cataract surgery.
These include the creation of the initial surgical incision in the cornea, the
creation of the capsulotomy and the phacofragmentation, the initial
fragmenting of the lens. The femtosecond laser may also produce incisions
within the peripheral cornea to aid the correction of pre-existing astigmatism
.
Femtosecond laser energy is absorbed by the tissue, resulting in plasma
formation. This plasma of free electrons and ionized molecules rapidly
expands, creating cavitation bubbles. The force of the cavitation bubble
creation separates the tissue. The process of converting laser energy into
mechanical energy is known as photodisruption.
Currently, 4 femtosecond laser technology platforms are commercially
available for cataract surgery:
Catalys (Optimedica), Lensx (Alcon Laboratories, Inc.), Lensar (Lensar, Inc.),
Victus (Technolas).
Preoperative Planning for FLACS Surgery:
First, detailed planning of each stage of the operation is required.
This involves:
• assessing the anatomy of the patient's eye
• taking into account pupil diameter
• anterior chamber depth, and thickness of the lens and cornea.
Size, shape, and centration of the capsulotomy are then calculated, with the choice
of IOL in mind. The type of lens fragmentation or liquefaction is chosen and
customised by the surgeon, as this will have a bearing on the amount of phaco time
and power, which is required subsequently. Parameters for the location, structure,
and depth of the clear corneal incisions (CCIs) are inputted. If astigmatic relieving
incisions are to be performed, their depth, length, and axis are currently determined
by traditional nomograms.
PROCEDURE FOR FLACS:
• Docking
Proper docking requires the patient to be flat on the table with minimal
neck support. The head must be secured with a slight tilt so the operated
eye is in a higher plane to clear the nose and achieve proper applanation.
The patient must be able to remain still for the several minutes required
for accurate imaging followed by application of laser energy.
There are also different patient-interface systems, which can be divided
into contact (applanating) and noncontact (nonapplanating).
Contact systems tend to have a smaller diameter and may fit a smaller
orbit better. They also provide a separate reference plane for anterior
cuts such as a flap.
Noncontact devices, in addition to less increase in intraocular pressure
(IOP), cause less subconjunctival hemorrhage and offer a wider field of
view.
• Imaging
All the femtosecond laser platforms use either spectral-domain optical
coherence tomography (OCT) or ray-tracing reconstruction (3-dimensional
confocal structural illumination [3-D CSI]) to image and map the treatment
plan .
The cornea must be centered within the applanated area to adequately
center the treatment. If not, capsulorhexis could be decentered, potentially
resulting in decentration of the intraocular lens (IOL).
It is crucial in astigmatic patients in whom decentration could result in arcuate
incisions within the visual axis or a wound posterior to the limbus.
During the acquisition phase, the patient must remain still for up to a few
minutes while the image is being captured.
The capsulorhexis is then centered within the pupillary border.
• The Treatment Stage
The diameter of the capsulorhexis is typically defined in settings
prior to the procedure (approximately 5.0 mm in most
cases) but can be modified according to pupillary dilation and IOL
selection.
The surgeon chooses a lens fragmentation pattern based on the
density of the nucleus and surgeon preference. They may choose the
number of segments as well as the degree of lens softening depending
on the lens grade. Commonly used patterns include 4, 6, or 8
segments with or without the use of lens softening.
A surgeon-defined safety zone from the posterior capsule (typically
500 to 800 mm) is automatically applied by the imaging platform and
visualized on the OCT guidance for approval by the surgeon before the
laser is applied.
The capsulorhexis is performed first and takes 1.5 to 18.0 seconds,
followed by lens fragmentation and ultimately corneal wound
creation.
Each laser incision is constructed in the posteroanterior
plane, a principle that elegantly employs the posterior
microcavitation bubbles to scatter the laser beam and
reduce the amount of energy reaching the retina. By
keeping the bubbles posterior to the laser target, the focus
of the laser beam is maintained and this avoids scatter
before the target tissue.
Once the laser treatment has been completed, the
suction is released, the patient interface is removed,
and the patient is slowly undocked from the laser.
Then the surgeon can proceed with phacoemulsification
immediately or wait up to 2 to 3 hours between the 2
stages of the procedure.
Due to progressive pupillary miosis, it is recommended
that phacoemulsification occur within 30 to 40 minutes of
the femtosecond laser procedure.
Femtosecond laser currently has four applications in cataract surgery:
astigmatic limbal relaxing incisions (LRIs), corneal wound construction,
anterior capsulotomy (or laser-incised capsulorhexis), and lens
fragmentation.
http://www.youtube.com/watch?v=r5kwgxdI-SE
Femtosecond laser in ophthalmology:
We stand at the threshold of a revolution, which is guided by the
femtosecond laser. With its expanding repertoire of uses, this laser
will soon be used in almost every aspect of ophthalmic science. From
its beginning in LASIK, it has gone on to Intra-Corneal Ring Segments
and keratoplasties. The femtosecond laser is now going to treat
cataracts. From capsulotomy to nuclear softening and chopping as
well as creation of side ports and corneal incisions, everything is now
possible with the femtosecond laser.
It uses an infrared beam of light to precisely separate tissue through
a process called photodisruption by generating pulses as short as
one-quadrillionth of a second. It has wavelength of 1053 nm and is
based on the technology whereby focused laser pulses divide
material at the molecular level without transfer of heat or impact to
the surrounding tissue.
Its most popular use lies in the creation of a corneal flap in a lasik
procedure. The laser beam is focused on a pre-programmed depth
and position within the cornea with each pulse forming a microscopic
bubble. As the laser moves painlessly back and forth, the bubbles
connect to form a flap with no trauma, the entire process taking
around 10-20 seconds. The surgeon then lifts the flap to allow
treatment by excimer laser.
The laser also creates a distinctive beveled edge flap which allows
precise repositioning and alignment after Lasik is completed.
The precision of the femtosecond laser helps to create flaps of exact
size, shape and depth and reduces the risk of blade-related
complications such as free caps, incomplete or decentered flaps.
Also, visual acuity is better and post-op dry eye symptoms are
reduced. It also creates fewer high and low-order aberrations which
may cause glare and haloes at night.
The femtosecond laser has also revolutionized other forms of corneal
surgery such as corneal transplantation and Intrastromal ring
implantation. It enables surgeons to create straight, angled and
arcuate incisions which allow faster healing and improved visual
recovery in penetrating keratoplasty.
The mushroom shaped incision preserves more host endothelium. The
“zigzag” incision approach provides a smooth transition between host
and donor tissue and allows for a hermetic wound seal, Intralase
Enabled Keratoplasty establishes secure grafts requiring less suture
tension and reduce incidence of astigmatism leading to a faster and
better visual recovery.
The femtosecond laser is also used for insertion of intra-corneal ring
segments (ICRS) in the treatment of keratoconus and corneal ectasia.
It creates channels at a pre-determined depth with a high degree of
accuracy. The entry wound and channel creation takes 8-10 seconds
after which the entry wound is opened with a Sinskey hook and the
ring segment is carefully pushed forward in the channel till the edge
lies within 1 mm from the entry wound.
The introduction of newer generations of femtosecond lasers which
have a higher frequency, offer greater precision, control and safety
and reduce the time spend during the procedure. Additional features
include variation in the flap shape and diameters to allow for
elliptical flaps for better results in hyperopic patients. Another
feature is the change in angulation of the flap edge to achieve a
better flap apposition and more secure flap healing with greater
stability.
A study of the LenSx laser at Semmelweis University in Budapest,
Hungary, found that all anterior capsulotomies created with the laser
achieved accurate centration and intended diameter, with no radial
tears or adverse events. Only 10% of manually created
capsulorhexes achieved a similar diameter accuracy of ± 0.25 mm.
The results were reported at the 2009 American Academy of
Ophthalmology meeting.
Clinical Results:
Femtosecond laser-assisted corneal incision
Masket et al., conducted a cadaver eye study in which they showed decreased
leakage, added stability, and reproducibility at various IOPs after FSL-guided
corneal incision. Additionally, Palanker et al., observed they could create an
incision using the FSL that formed a one-way, self-sealing, and water-tight valve
under normal IOP. No authors have published data on the rate of postoperative
endophthalmitis with the advent of FSL-guided incision in cataract surgery, and
there are no published comparative studies between standard keratome and
FSL-guided incisions.
Femtosecond laser-assisted capsulorhexis
Nagy et al., performed anterior capsulotomies in 54 eyes, comparing the LenSx
laser to manual capsulorhexis 1 week after cataract surgery. In the FSL group,
the authors observed a higher degree of circularity, fewer patients with
incomplete capsulorhexis-IOL overlap (11% of laser patients compared to 28%
of manual capsulorhexis patients), and better IOL centration.
FSL-guided capsulotomy diameter did not show correlation
to pupil diameter, eye size, or curvature of the cornea,
assuming the pupil was appropriately dilated.
However, manual capsulotomy size was directly correlated
with these variables. This suggests that manual
capsulotomy is prone to deceptive influence from the pupil
size, eye size, and curvature of the cornea, while laser
capsulotomy avoids this inappropriate influence.
Using the OptiMedica FSL platform, two studies similarly
demonstrated a statistical advantage for the FSL-assisted
capsulotomy in terms of precision, accuracy, and
reproducibility in human eyes.
Femtosecond laser-assisted phacofragmentation
Preliminary work has shown that FSL systems reduce ultrasound
energy necessary for all grades of cataract. Nagy et al., showed that the
FSL reduced phacoemulsification power by 43% and operative time by
51% in a porcine eye study. Two studies have compared human eyes
receiving FSL-assisted capsulorhexis and phacofragmentation to fellow
eyes receiving traditional cataract surgery. Both show easier
phacoemulsification in the FSL group. In one of these studies, Palanker
et al. observed a decrease in the perceived hardness of nuclear sclerotic
cataract after the laser-assisted procedure, estimated by the surgeon
to decrease from grade four to grade two.
A 39% average reduction in dispersed energy for phacoemulsification
was also observed in the FSL group. Furthermore, they showed that
with grade three or higher cataracts, FSL-assisted lens fragmentation
also reduced the amount of energy, suggesting fewer complications for
these more difficult cataracts.
The introduction of femtosecond lasers to cataract surgery has
generated much interest among ophthalmologists around the world.
Laser cataract surgery integrates high-resolution anterior segment
imaging systems with a femtosecond laser, allowing key steps of the
procedure, including the primary and side-port corneal incisions, the
anterior capsulotomy and fragmentation of the lens nucleus, to be
performed with computer-guided laser precision. There is emerging
evidence of reduced phacoemulsification time, better wound
architecture and a more stable refractive result with femtosecond
cataract surgery.
Also, Femtosecond laser surgery is a great experience not only for the
surgeon, but also for the patient, because it offers very good results, is a
really fast procedure and is almost painless for the patient.
Limitations:
• Current studies support the safety and efficacy of FLACS, although
small patient populations and short-term follow-up limit the ability to
assess such safety factors as the frequency of discontinuous FSLassisted capsulorhexis and associated anterior capsular tears.
• There are a lot of unanswered questions at this point. For FSL-assisted
corneal incision, , it is important to research the difference in
postoperative endophthalmitis rates after laser-assisted corneal
incision. Although this research will be a difficult, because it requires
very large patient populations, this is a key question because
postoperative endophthalmitis is the terminal outcome measure that
will ultimately justify FSL use in corneal incisions.
There are no available studies using large enough patient populations
to accurately assess complication rates. The longest study is limited to
1 year of follow-up. This study focused on centration parameters only.
• The limitations of FLACS are not well-established at this time. Based
on relative contraindications to FSL refractive surgery, we
hypothesize similar contraindications may apply to FLACS. Logically
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. Other exclusions may be anterior basement
membrane dystrophy, corneal opacities (e.g. arcus senilis, corneal
dystrophies, and trauma- or contact lens-induced scars), ocular
surface disease, pannus with encroaching blood vessels, or recurrent
epithelial erosion syndrome.
• The level of increase in IOP induced by the docking device has not
been adequately quantified. This may be an important
contraindication for patients with glaucoma, optic neuropathies, or
borderline endothelial pathology. Lastly, diabetics may have
undiagnosed epithelial disease making them prone to epithelial
defects.
• Because FLACS relies on anterior segment imaging for laser pattern
mapping, any patients with poor dilation would be poor candidates.
Such patients would be those with posterior synechiae,
intraoperative floppy iris syndrome suspects, or those on chronic
miotic medications. High-quality images for mapping of the
posterior lens are critical.
• More studies are also needed to assess if dense posterior
subcapsular cataracts, those with vacuoles, anterior subcapsular
cataracts, and other types or combinations of cataracts will perform
differently with FSL-assisted phacofragmentation.
Additionally, having a stable, stationary lens is needed for precise laser
mapping and execution. Patients with phacodonesis and zonular
dialysis, or those with risk factors such as pseudoexfoliation types or
combinations of cataracts will perform differently with FSL-assisted
phacofragmentation.
• A stable, stationary lens is needed for precise laser mapping and
execution. Patients with phacodonesis and zonular dialysis, or those
with risk factors such as pseudoexfoliation syndrome or trauma, may
not be ideal candidates.
• The final issue for FLACS is cost. There is no doubt that this
technology has added costs, although we have seen that patients are
willing to pay out of pocket for new technology if they view it as
being safer or offering better results. Similarly, patients will likely be
willing to pay extra if they perceive that they will achieve better
results with laser- assisted cataract surgery.
• Cost-benefit analysis has not yet been addressed.