Technological
development
The LASIK technique was made possible by the
Colombian-based
Spanish
ophthalmologist
Jose Barraquer, who, around 1950 in his clinic in
Bogotá,
Colombia, developed the first
microkeratome, used to cut thin flaps in the
cornea
and alter its shape, in a procedure called
keratomileusis. He also provided the knowledge about how much of the
cornea had to be left unaltered to provide a stable long-term result.
Later technical and procedural developments included the RK (radial
keratotomy) started in the '70s in Russia by Svyatoslav Fyodorov and the
development of PRK (photorefractive keratectomy) in the '80s in Germany
by Theo Seiler.
In 1968, at the Northrup Corporation Research and Technology Center
of the
University of California,
Mani Lal Bhaumik and a group of other scientists, while working on
the development of a carbon-dioxide laser, would develop the
Excimer laser, where molecules that do not normally exist come into
being when xenon, argon or krypton gases are excited. This would form
the cornerstone for LASIK eye surgery. Dr. Bhaumik announced his
discovery in May of 1973 at a meeting of the Denver Optical Society of
America in
Denver, Colorado. He would later patent it.
[1]
The introduction of Laser in this refractive procedure started with
the developments in Laser technology by
Rangaswamy Srinivasan. In 1980, Srinivasan, working at
IBM Research Lab, discovered that an ultraviolet
excimer laser could etch living tissue in a precise manner with no
thermal damage to the surrounding area. He named the phenomenon Ablative
Photodecomposition (APD).[2].
Dr. Stephen Trokel published a paper in the American Journal of
Ophthalmology in 1983, outlining the potential of using the excimer
laser in refractive surgeries.
The first patent for LASIK was granted by the US Patent Office to
Gholam A. Peyman, MD on June 20, 1989, US Patent #4,840,175, "METHOD FOR
MODIFYING CORNEAL CURVATURE", describing the surgical procedure in which
a flap is cut in the cornea and pulled back to expose the corneal bed.
This exposed surface is then ablated to the desired shape with an
excimer laser, following which the flap is replaced.
Using these advances in laser technology and the technical and
theoretical developments in refractive surgery made since the 50's,
LASIK surgery was developed in 1990 by Lucio Buratto (Italy)
and Ioannis Pallikaris (Greece)
as a melding of two prior techniques,
keratomileusis and photorefractive
keratectomy. It quickly became popular because of its greater
precision and lower frequency of complications in comparison with these
former two techniques. Today, faster lasers, larger spot areas,
bladeless flap incision, and wavefront-optimized and -guided techniques
have significantly improved the reliability of the procedure as compared
to that of 1991. Nonetheless, the fundamental limitations of excimer
lasers and undesirable destruction of the eye's nerves have spawned
research into many alternatives to "plain" LASIK, including all-femtosecond
correction (Femtosecond
Lenticule EXtraction,
FLIVC),
LASEK,
Epi-LASIK,
sub-Bowman’s Keratomileusis aka thin-flap LASIK,
wavefront-guided PRK, and modern
intraocular lenses.
Procedure
There are several necessary preparations in the preoperative period.
The operation itself is made by creating a thin flap on the eye, folding
it to enable remodeling of the tissue underneath with laser. The flap is
repositioned and the eye is left to heal in the postoperative period.
Preoperative
Patients wearing soft
contact lenses typically are instructed to stop wearing them
approximately 5 to 7 days before surgery. One industry body recommends
that patients wearing hard contact lenses should stop wearing them for a
minimum of six weeks plus another six weeks for every three years the
hard contacts had been worn.
[3] Before the surgery, the patient's
corneas
are examined with a
pachymeter to determine their thickness, and with a topographer to
measure their surface contour. Using low-power
lasers, a
topographer creates a
topographic map of the cornea. This process also detects
astigmatism and other irregularities in the shape of the cornea.
Using this information, the surgeon calculates the amount and locations
of corneal tissue to be removed during the operation. The patient
typically is prescribed an antibiotic to start taking beforehand, to
minimize the risk of infection after the procedure.
Operation
The operation is performed with the patient awake and mobile;
however, the patient typically is given a mild
sedative (such as
Valium) and anesthetic
eye
drops.
LASIK is performed in three steps. The first step is to create a flap
of corneal tissue. The second step is remodeling of the cornea
underneath the flap with laser. Finally, the flap is repositioned.
Flap
creation
A corneal suction ring is applied to the eye, holding the eye in
place. This step in the procedure can sometimes cause small blood
vessels to burst, resulting in bleeding or
subconjunctival hemorrhage into the white (sclera)
of the eye, a harmless side effect that resolves within several weeks.
Increased suction typically causes a transient dimming of vision in the
treated eye. Once the eye is immobilized, the flap is created. This
process is achieved with a mechanical
microkeratome using a metal blade, or a
femtosecond laser microkeratome (procedure known as
IntraLASIK) that creates a series of tiny closely arranged bubbles
within the cornea.[4]
A hinge is left at one end of this flap. The flap is folded back,
revealing the
stroma,
the middle section of the cornea. The process of lifting and folding
back the flap can be uncomfortable.
Laser
remodeling
The second step of the procedure is to use an
excimer laser (193 nm) to remodel the corneal stroma. The laser
vaporizes tissue in a finely controlled manner without damaging
adjacent stroma. No burning with heat or actual cutting is required to
ablate the tissue. The layers of tissue removed are tens of
micrometers thick. Performing the laser ablation in the deeper
corneal stroma typically provides for more rapid visual recovery and
less pain, than the earlier technique
photorefractive keratectomy (PRK).
During the second step, the patient's vision will become very blurry
once the flap is lifted. He/she will be able to see only white light
surrounding the orange light of the laser. This can be disorienting.
Currently manufactured excimer lasers use an eye tracking system that
follows the patient's eye position up to 4,000 times per second,
redirecting laser pulses for precise placement within the treatment
zone. Typical pulses are around 1 mJ of pulse energy in 10 to 20
nanoseconds.[2]
Reposition
of flap
After the laser has reshaped the stromal layer, the LASIK flap is
carefully repositioned over the treatment area by the surgeon, and
checked for the presence of air bubbles, debris, and proper fit on the
eye. The flap remains in position by natural adhesion until healing is
completed.
Postoperative
Patients are usually given a course of antibiotic and
anti-inflammatory eye drops. These are continued in the weeks following
surgery. Patients are also given a darkened pair of shields to protect
their eyes from bright lights and protective goggles to prevent rubbing
of the eyes when asleep and to reduce dry eyes. They also have to
moisturize the eyes with preservative free tears and follow directions
for prescription drops. Patients should be adequately informed by their
surgeons of the importance of proper post-operative care to minimize the
risk of post-surgical complications.
Higher-order
aberrations
Higher-order
aberrations are visual problems not captured in a traditional eye
exam which tests only for acuteness of vision. Severe aberrations can
effectively cause significant vision impairment. These aberrations
include starbursts, ghosting, halos, double vision, and a number of
other post-operative complications listed below.
Concern has long plagued the tendency of refractive surgeries to
induce higher-order aberration not correctable by traditional contacts
or glasses. The advancement of LASIK technique and technologies has
helped reduce the risk of clinically significant visual impairment after
the surgery. One of the major discoveries was the correlation between
pupil size and aberrations:[3]
Effectively, the larger the pupil size, the greater the risk of
aberrations. This correlation is the result of the irregularity between
the untouched part of the cornea and the reshaped part. Daytime post-lasik
vision is optimal, since the pupil is smaller than the LASIK flap. But
at night, the pupil may expand such that light passes through the edge
of the LASIK flap into the pupil which gives rise to many aberrations.
There are other currently unknown factors in addition to pupil size that
also affect higher order aberrations.
In extreme cases, where ideal technique was not followed and before
key advances, some people could suffer rather debilitating symptoms
including serious loss of contrast sensitivity in poor lighting
situations.
Over time, most of the attention has been focused on
spherical aberration. LASIK and PRK tend to induce spherical
aberration, because of the tendency of the laser to undercorrect as it
moves outward from the center of the treatment zone. This is really a
significant issue for only large corrections. There is some thought if
the lasers were simply programmed to adjust for this tendency, no
significant spherical aberration would be induced. Hence, in eyes with
little existing higher order aberrations, "wavefront optimized" LASIK
rather than wavefront guided LASIK may well be the future.[citation
needed]
In any case, higher order aberrations are measured in µm
(micrometers) on the wavescan taken during the pre-op examination, while
the smallest beam size of
FDA approved lasers is about 1000 times larger, at 0.65 mm. Thus
imperfections are inherent in the procedure and a reason why patients
experience halo, glare, and starburst even with small naturally dilated
pupils in dim lighting.
Wavefront-guided
LASIK
Wavefront-guided LASIK[4]
is a variation of LASIK surgery where, rather than applying a simple
correction of focusing power to the cornea (as in traditional LASIK), an
ophthalmologist applies a spatially varying correction, guiding the
computer-controlled excimer laser with measurements from a wavefront
sensor. The goal is to achieve a more optically perfect eye, though the
final result still depends on the physician's success at predicting
changes which occur during healing. In older patients though,
scattering from microscopic particles plays a major role and may
exceed any benefit from wavefront correction. Hence, patients expecting
so-called "super vision" from such procedures may be disappointed.
However, while unproven, surgeons claim patients are generally more
satisfied with this technique than with previous methods, particularly
regarding lowered incidence of "halos", the visual artifact caused by
spherical aberration induced in the eye by earlier methods.
Complications
The incidence of refractive surgery patients having unresolved
complications six months after surgery has been estimated from 3%[5]
to 6%.[6]
The risk for a patient of suffering from disturbing visual side effects
like
halos,
double
vision (ghosting), loss of
contrast sensitivity (foggy vision) and
glare after LASIK depends on the degree of
ametropia before the laser eye surgery and other risk factors.[7]
For this reason, it is important to take into account the individual
risk potential of a patient and not just the average probability for all
patients.[8]
The following are some of the more frequently reported complications of
LASIK[9][5]:
Complications due to LASIK have been classified as those that occur
due to preoperative, intraoperative, early postoperative, or late
postoperative sources:[18]
Intraoperative
complications
- The incidence of flap complications has been estimated to be
0.244%.[19]
Flap complications (such as displaced flaps or folds in the flaps
that necessitate repositioning, diffuse lamellar keratitis, and
epithelial ingrowth) are common in lamellar corneal surgeries[20]
but rarely lead to permanent visual acuity loss; the incidence of
these microkeratome-related complications decreases with increased
physician experience.[21][22]
According to proponents of such techniques, this risk is further
reduced by the use of
IntraLasik and other non-microkeratome related approaches,
although this is not proven and carries its own set of risks of
complications from the
IntraLasik procedure.
- A slipped flap (a corneal flap that detaches from the rest of
the cornea) is one of the most common complications. The chances of
this are greatest immediately after surgery, so patients typically
are advised to go home and sleep to let the flap heal. Patients are
usually given sleep goggles or eye shields to wear for several
nights to prevent them from dislodging the flap in their sleep. A
faster operation may decrease the chance of this complication, as
there is less time for the flap to dry.
- Flap interface particles are another finding whose clinical
significance is undetermined.[23]
A Finnish study found that particles of various sizes and
reflectivity were clinically visible in 38.7% of eyes examined via
slit lamp biomicroscopy, but apparent in 100% of eyes using
confocal microscopy.[23]
Early
postoperative complications
- The incidence of diffuse lamellar keratitis (DLK)[6],
also known as the Sands of Sahara syndrome, has been estimated at
2.3%.[24]
When diagnosed and appropriately treated, DLK resolves with no
lasting vision limitation.
- The incidence of infection responsive to treatment has been
estimated at 0.4%.[24]
Infection under the corneal flap is possible. It is also
possible that a patient has the genetic condition
keratoconus that causes the cornea to thin after surgery.
Although this condition is screened in the preoperative exam, it is
possible in rare cases (about 1 in 5,000) for the condition to
remain dormant until later in life (the mid-40s). If this occurs,
the patient may need rigid gas permeable contact lenses,
Intrastromal Corneal Ring Segments (Intacs),[25]
Corneal Collagen Crosslinking with Riboflavin[26]
or a corneal transplant.
- The incidence of persistent dry eye has been estimated to be as
high as 28% in Asian eyes and 5% in Caucasian eyes.[6]
Nerve fibers in the cornea are important for stimulating tear
production. A year after LASIK, subbasal nerve fiber bundles remain
reduced by more than half.[27]
Some patients experience reactive tearing, in part to compensate for
chronic decreased basal wetting tear production.
- The incidence of subconjunctival hemorrhage has been estimated at
10.5%
[24](according to a study undertaken in China; thus
results may not be generally applicable due to racial and geographic
factors).
Late
postoperative complications
- The incidence of epithelial ingrowth has been estimated at 0.1%.[24]
-
Glare is another commonly reported complication of those who have
had LASIK.[28]
- Halos or starbursts around bright lights at night are caused by the
irregularity between the lasered part and the untouched part. It is not
practical to perform the surgery so that it covers the width of the
pupil at full dilation at night, and the pupil may expand so that light
passes through the edge of the flap into the pupil.[29]
In daytime, the pupil is smaller than the edge. Modern equipment is
better suited to treat those with large pupils, and responsible
physicians will check for them during examination.
- Late traumatic flap dislocations have been reported 1–7 years
post-LASIK.[30]
Other
Lasik and other forms of laser refractive surgery (i.e. PRK, LASEK
and Epi-LASEK) change the dynamics of the cornea. These changes make it
difficult for your optometrist and ophthalmologist to accurately measure
your intraocular pressure, essential in
glaucoma screening and treatment. The changes also affect the
calculations used to select the correct intraocular lens implant when
you have cataract surgery. This is known to ophthalmologists as
"refractive surprise." The correct intraocular pressure and intraocular
lens power can be calculated if you can provide your eye care
professional with your preoperative, operative and postoperative eye
measurements.
Although there have been improvements in LASIK technology[31][32][33],
a large body of conclusive evidence on the chances of long-term
complications is not yet established. Also, there is a small chance of
complications, such as haziness, halo, or glare, some of which may be
irreversible because the LASIK eye surgery procedure is irreversible.
The incidence of
macular hole has been estimated at 0.2 percent[17]
to 0.3 percent.[34]
The incidence of
retinal detachment has been estimated at 0.36 percent.[34]
The incidence of
choroidal neovascularization has been estimated at 0.33 percent.[34]
The incidence of
uveitis
has been estimated at 0.18 percent[35]
Although the cornea usually is thinner after LASIK, because of the
removal of part of the stroma, refractive surgeons strive to maintain a
minimum thickness to avoid structurally weakening the cornea. Decreased
atmospheric pressure at higher altitudes has not been demonstrated as
extremely dangerous to the eyes of LASIK patients. However, some
mountain climbers have experienced a myopic shift at extreme
altitudes.[36][37]
There are no published reports documenting scuba diving-related
complications after LASIK.[38]
In situ keratomileusis effected at a later age increases the
incidence of corneal higher-order wavefront aberrations.[39][40]
Conventional eyeglasses do not correct higher order aberrations.
Microfolding has been reported as "an almost unavoidable
complication of LASIK" whose "clinical significance appears negligible."[23]
Blepharitis, or inflammation of the eyelids with crusting of the
eyelashes, may increase the risk of infection or inflammation of the
cornea after LASIK.[41]
Myopic (nearsighted) people who are close to the age (mid- to
late-forties) when they will require either reading glasses or bifocal
eyeglasses may find that they still require reading glasses despite
having undergone refractive LASIK surgery. Myopic people generally
require reading glasses or bifocal eyeglasses at a later age than people
who are emmetropic (those who see without eyeglasses), but this benefit
is lost if they undergo LASIK. This is not a complication but an
expected result of the physical laws of optics. Although there is
currently no method to completely eradicate the need for reading glasses
in this group, it may be minimized by performing a variation of the
LASIK procedure called "slight
monovision." In this procedure, which is performed exactly like
distance-vision-correction LASIK, the dominant eye is set for distance
vision, while the non-dominant eye is set to the prescription of the
patient's reading glasses. This allows the patient to achieve a similar
effect as wearing bifocals. The majority of patients tolerate this
procedure very well and do not notice any shift between near and
distance viewing, although a small portion of the population has trouble
adjusting to the monovision effect. This can be tested for several days
prior to surgery by wearing contact lenses that mimic the monovision
effect.
Factors
affecting surgery
Typically, the cornea is avascular because it must be transparent to
function normally, and its cells absorb
oxygen
from the tear
film. Thus, low-oxygen-permeable contact lenses reduce the cornea's
oxygen absorption, sometimes resulting in
corneal neovascularization—the growth of blood vessels into the
cornea. This causes a slight lengthening of inflammation duration and
healing time and some pain during surgery, because of greater bleeding.
Although some contact lenses (notably modern RGP and soft silicone
hydrogel lenses) are made of materials with greater oxygen permeability
that help reduce the risk of corneal neovascularization, patients
considering LASIK are warned to avoid over-wearing their contact lenses.
Usually, it is recommended that they discontinue wearing contact lenses
days or weeks before the LASIK eye surgery.
A 2004
Wake Forest University study established that heat and humidity
affect LASIK surgery results, both during the procedure and in the two
weeks before the surgery.[42]
Age
considerations
New advances in eyesight corrective surgery are providing consumers
greater choices. Patients in their 40s or 50s who are considering LASIK
surgery to improve their vision might want to consider to be evaluated
for implantable lenses as well. "Early signs of a cataract might argue
for surgery and implantation of multifocal lenses instead."
[43]
Patient
satisfaction
The surveys determining patient satisfaction with LASIK have found
most patients satisfied, with satisfaction range being 92–98 percent.[28][44][45][46]
A meta-analysis dated March 2008 performed by the American Society of
Cataract and Refractive Surgery over 3,000 peer-reviewed articles
published over the past 10 years in clinical journals from around the
world, including 19 studies comprising 2,200 patients that looked
directly at satisfaction, revealed a 95.4 percent patient satisfaction
rate among LASIK patients worldwide.
[47]
Some patients with poor outcomes from LASIK surgical procedures
report a significantly reduced quality of life because of vision
problems. Patients who have suffered LASIK complications have created
websites and discussion forums to educate the public about the risks,
where prospective and past patients can discuss the surgery. In 1999,
Surgical Eyes
[48]
was founded
[49]
in New York City
[50]
[51]as
a resource for patients with complications of LASIK and other refractive
surgeries. Other patient-founded websites to assist those with
complications are
LaserMyEye
[52]]
founded
[53]
in 2004 and
Vision Surgery Rehab
[54]
[55]
in 2005.[56]Most
experienced and reputable clinics will do a full-dilated medical eye
exam prior to surgery and give adequate post-operative patient education
care to minimize the risk of a negative outcome.
Dr. Steven Schallhorn, an ophthalmologist who oversaw the
A1
Health Care
