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There are 4 makes of femtosecond laser on the market as of Oct 2008. The one we can use is one made by Ziemer. There is an independent article written by Dr Omid Kermani from Cologne which is useful to read and tells of his group's first year experience of the Intralase system.. I have scanned it from a magazine (March 2006) with 3 pages: Page 1 Page 2 Page 3. I have been trained and certified by Intralase.
In the ESCRS congress in Berlin in September 2008, there were a couple of papers comparing mechanical and femtosecond lasers. No difference was found between them
The main practical difference might be that there are slightly less complications with femtosecond lasers rather than mechanical microkeratomes. My own opinion, having used the Intralase system is that both systems have an extremely low rate of complications and these vary in nature between the two systems. The bulletin board for certified Intralase surgeons seems to have complications more often than the manufacturer indicates in their sales literature. Dr Jose Geull, a highly respected surgeon from Barcelona, says in a recent article (Eurotimes 4 April 2009) "visual outcomes with both microkeratome and femtosecond laser flaps are virtually identical....I think that the question about which technology is better for flap creation is really a market-driven question" I use the Morial microkeratome system, which gives us the choice of flaps of various thicknesses - 100, 110, 130 and 150 microns. I use both the Moria M2 and the Moria One Use Plus systems. The new Moria SBK (Sub Bowmans Keratomeilusis) microkeratome head cuts 100 micron thin flaps. Performance equivalent to IntraLase
60kHz - ESCRS Congress Berlin 2008
In the January 2009 issue of Cataract & Refractive
Surgery Today Europe, Daniel Casado Rodríguez, MD (Madrid, Spain) reported the
results in a series of 200 consecutive eyes treated with the One Use-Plus
SBK5: With either type of ring, the One Use-Plus SBK provided
excellent, consistent 100-micron flap thickness (measured by ultrasound
pachymetry):
The Moria One
Use-Plus SBK microkeratome with: With the use of an anterior segment Optical Coherence Tomography technology (Visante®, Carl Zeiss Meditec, Jena, Germany), flap thickness was assessed horizontally and vertically, at 1.5 and 3mm from the apex nasally and temporally. The planar profile was demonstrated with both types of rings.
On the basis of these and other studies Moria claims that the SBK microkeratome head has the following characteristics
We are just starting to use this particular head and will see if our results match these (April 2009)
Moria SBK with Single Use ring
How a Femtosecond Laser Works:
INTRALASE LASER:
The excimer laser, which is ultraviolet, works on the surface and is called "photoablation" These femtosecond lasers, which are infrared, work in the middle of the cornea and is called "photodisruption" Thousands of very small bubbles are joined together to make a cornea flap very precisely and safely.
Protocol
for Femtosecond Note:
Femtosecond is the generic name. IntraLase
is the trade name. Procedure 1.
The patient should not wear make up, hairspray, perfume, aftershave or
strong deodorant on the day of surgery. They should bring sunglasses with them
on the day of surgery. 2.
The patient is called into the first laser room, where anaesthetic drops
are put in their eye. These may sting a little bit. 3.
The patient then lies down on a reclining chair underneath the
femtosecond laser. One of their eyes will be taped. 4.
A suction ring is placed on the other eye. This will increase the
pressure in the eye. Some patients can find this uncomfortable and the vision
can black out for about 60 seconds. 5.
Once the ring is at the correct pressure, the laser will start. 6.
The patient won’t feel or hear anything while the laser is operational. 7.
The femtosecond laser creates a flap with a hinge through infrared laser
energy that inserts a precise pattern of tiny, overlapping bubbles just below
the front surface of the eye. These bubbles can take up to 10 minutes to fully
dissipate. 8.
The creation of the flap takes about 45 seconds. 9.
Once the laser is finished, the suction ring is removed from the first
eye and placed on the second eye, where the procedure is repeated. 10.
Once the flap has been created on the second eye, the patient remains
lying on the reclining chair for 10 to 15 minutes, while the bubbles formed by
the laser dissipate. 11.
Then the patient is taken from the first laser room to the second laser
room. 12.
An eyelid clamp is placed on the eyelids to help prevent blinking during
the second part of the procedure. 13.
The flap created by the femtosecond laser is lifted by the surgeon. The
flap is then flipped over at the hinge and the laser treatment is carried out
underneath the flap. 14.
While the laser is working, the patient will hear a snapping noise and
there will be a smell similar to burning hair. Again the patient won’t feel
anything. 15.
During the laser procedure the patient will be asked to look at a
fixation light. If the patient looses fixation, the laser has an iris tracker
that will follow movements of their eye. The laser may stop and start for
reasons of prescription (astigmatism) or fixation. One eye may take longer than
the other. 16.
Once the laser is finished, the surgeon replaces the flap and slowly
removes the eyelid clamp allowing the patient to blink. 17.
The surgeon then moves on to the second eye. The whole procedure for both
eyes takes approximately 20 minutes. Aftercare The aftercare regime is the same as it
would be for LASIK performed with a microkeratome. History
of Femtosecond The first femtosecond initiated LASIK
procedure in the US was carried out in April 2000. Follow up data for Intralase is available for the last four years. Complications
& Considerations Retreatment after
Femtosecond The retreatment procedure is the same
regardless of whether the original treatment was with a mechanical keratome or
with the femtosecond laser. Retreatment can be carried out as soon as the
prescription is stable. 95% of flaps can be lifted after two years. Retreatment
rates after femtosecond are less by 30% - 40% compared to retreatment rates
after a mechanical microkeratome. DLK Inflammation as seen in post LASIK
with microkeratome patients is not seen with the femtosecond. A less serious
peripheral inflammation is seen. This is the cause of transient light
sensitivity. See below Transient
Light Sensitivity This was first seen in patients in
2003. It occurs 2 - 6 weeks post operatively. It is usually treated with
steroids and clears up after about 1 - 4 weeks. This occurred in up to 20% of
patients in some studies with high initial energy settings on the femtosecond
laser. Following reductions in laser energy settings and based on collected
cases, it is thought to occur with about 1% of patients. Minor Flap
Complications Sometimes there can be wrinkles in the flap
or debris under the flap and the surgeon may need to lift the flap on one of the
early post-operative aftercares. The laser will not have to be applied again at
this point. Incomplete
Flaps & Buttonholes If there is loss of suction with the
IntraLase procedure while the flap is being cut, suction can be reapplied and
the cutting can continue. Because of this, the femtosecond laser does not create
incomplete flaps or buttonholes (where the centre of the flap remains uncut) and
is particularly good for patients with tight eyelids and deep set eyes. Flap
Thickness The thickness of femtosecond flaps is
more uniform and predictable than flaps created with a mechanical microkeratome.
Numerous studies have confirmed this including a study on 1000 consecutive LASIK
flaps created with the IntraLase laser carried out by Perry Binder. This means
that some patients with thinner corneas, who may previously have been unsuitable
for LASIK may now be suitable. The ability to more accurately predict flap
thicknesses means that surgeons can more accurately predict residual stromal
bed. Maintaining a residual stromal bed of >300 microns, helps to prevent the
formation of post Lasik ectasia (forward bulging of the cornea). Night Glare Patients who have their LASIK flap cut
with the femtosecond laser rather than a mechanical blade can be expected to
have slightly less problems with night glare (haloes) for two reasons. The
femtosecond laser's accuracy in cutting flaps means that a greater area of the
eye's front surface is available for treatment. Large treatment zones are
associated with less night vision problems. Also in a study made of nine
patients where one eye had a flap created with a microkeratome and the other was
created with IntraLase, the IntraLase created flap created less
higher order aberrations. It is these aberrations which are usually
responsible for most night vision problems. Epithelial
Defects and Corneal Abrasions In a retrospective study of 375 eyes
by Stonecipher and Kezirian in 2003, no epithelial defects were observed among
patients who had had flaps cut with the IntraLase laser. In a retrospective
study done on 404 patients who had LASIK flaps cut with a microkeratome between
Jan 2002 and June 2002 8% had some form of epithelial defect. Dry Eyes A mechanical microkeratome blade
enters the cornea at a relatively shallow angle and ends deep in the highly
innervated central. This causes damage to the nerve endings, which as a result
can cause dry eyes. The femtosecond flap enters the cornea at a steeper angle
believed to preserve deep corneal innervation and thus dry eye tends to be less
of a problem after femtosecond LASIK. In a study of 300 eyes cut with a
microkeratome and 300 eyes cut with Intralase, 55% of the microkeratome patients
complained of dry eyes whereas only 15% of IntraLase patients did. Epithelial
Ingrowth The difference in flap structure means
that epithelial ingrowth is less likely in flaps created with the femtosecond
laser compared to those created with a mechanical blade (1 in 10,000). Reading
Spectacles If a patient is fully corrected for
distance then they will still require reading glasses in their 40s regardless of
procedure. Infection Infection following LASIK treatment is very rare (1 in 2,500). It is possible that it may be even rarer after femtosecond due to its sterile sys
Transient Light Sensitivity Syndrome (TLSS) describes a constellation of symptoms that can occur following LASIK with femtosecond laser flap creation. Patients with TLSS generally present with light sensitivity that is out of the ordinary, good UCVA and minimal slit lamp findings 2-6 weeks after uncomplicated LASIK. All patients responded to topical steroids, although improvement with Restasis (cyclosporine ophthalmic solution 0.05%, Allergan) has also been reported in one centre. Based on collected cases, an incidence of approximately 1% was identified. The highest incidence rates occurred with the highest initial energy settings and with reduction in the number of cases following reductions in laser energy settings by 20-60%. In best documented series there was an approximately 5 fold reduction in incidence to less than 0.2% following an approximately 20% lowering of surgical energies. |
The laser presses lightly
on the eye and then is activated to make the corneal flap. One of the advantages
of the flap as opposed to a flap made by a microkeratome is that it is the same
thickness throughout:
