Introduction to LASIK
LASIK is an acronym for laser in situ keratomileusis.
It is a very common corneal laser surgery used
to treat a wide range of refractive problems of
the eye including near and far sightedness and
astigmatism, and thus reduce dependence on glasses.
The advantages include less recovery period, less
painful and less intense healing response. Disadvantages
are some serious side effects which may cause blindness.
Besides, the procedure is expensive and needs highly
skilled people for safe operation.
Earlier, eye laser surgeries were done by a procedure
termed photorefractive keratectomy or PRK. This
procedure had drawbacks like, delayed recovery
time, discomfort and significant reduced vision
problems in a few cases. LASIK surgery is an improvement
on PRK in most respects.
The surgery is performed by an excimer laser.
At its simplest, the procedure uses an instrument
called a microkeratome or more recently, a femtosecond
laser. An epithelialstromal flap is cut and left
attached to the corneal periphery by a hinge of
uncut tissue. This flap is lifted and the high
energy pulses of the excimer laser are applied
on the stromal area to get the desired surgical
outcomes. After the operation, the flap is returned
to its original position. No sutures are needed
to heal the cut.
Benefits of LASIK
LASIK performed by skilled and experienced surgeons
improves vision substantially, in most cases, even
if vision acuity of 20/40 is not achieved. The
chances of getting a desired level of vision correction
are inversely related to baseline level of correction.
For example, in an eye with 2 dioptres of myopia
the chances of getting a 20/20 vision is 70% to
80%, and the chances of achieving 20/40 or better
is greater than 98%. Whereas, in an eye with myopia
of 9D, the odds of getting 20/20 vision are 40%
to 55% and odds of getting 20/40 vision are 95%
Depending on surgeon expertise and the initial
correction attempted, a repeat enhancement laser
ablation surgery is needed in 5% to 20% cases,
to obtain best outcomes. In LASIK, the tendency
to lose the surgical effects over time is comparatively
Risks from LASIK surgery
LASIK can result in several complications. These
are visual disturbances, such as, starbursts, halos,
distorted images, and multiple images commonly
seen during the night. The chances of these complications
occurring is more when excimer laser is used or
when corrections are higher than 7 to 8 dioptres
of myopia and 2 to 3 dioptres of hyperopia. Improved
laser technology and pre-operative screenings have
reduced the incidence of such complications to1%
of patients treated, according to a rough estimate.
Other complications like, infection and ectasia
are seen in less than 1% cases.
Unique to LASIK are the flap- induced complications,
not found in PRK or other laser surgeries since
they do not involve flaps. It is mainly due to
flap complications that LASIK carries a higher
risk of losing 2 or more lines of visual acuity
in Snellen’s chart. Flap formations in LASIK
also induce transient dry eyes in LASIK.
Haze in the anterior stroma due to wound is rare.
By and large, LASIK offers better comfort and vision
after a few days of surgery. Complications it appears
are less with more experienced surgeons.
Pre-operative screening for LASIK
Pre-operative screening is critical for good surgical
outcomes. Patients are comprehensively examined
for normal, healthy eyes. LASIK is performed only
on those above 21 years of age. And even in these
cases, refraction should have been relatively stable
in the previous two years. This may be difficult
to verify and the surgeon may have to rely on patient
LASIK is not considered a suitable option in people
with systemic diseases, such as, rheumatoid arthritis
and immune related disorders associated with healing
problems, such as, corneal melting. Pregnant and
lactating women also should not opt for LASIK due
to changes in refraction at that time. Patients
with moderate to severe dry eyes are not suitable
candidates for LASIK.
Corneal thickness, which is normally between 490
micro meters to 650 micro meters, should be taken
into account before opting for LASIK. LASIK should
be avoided if corneal thickness is inadequate,
even where corneal topography is normal.
Also important is pupil diameter in the dark.
Greater the pupil diameter in the dark, greater
is the likelihood of glare, halos and other visual
disturbances, especially in eyes with high myopia.
Therefore, measurements performed during the pre-operative
eye screening are especially vital in determining
the presence of myopia or hyperopia.
Topographic maps of the cornea should not show
any signs of diseases where progressive thinning
of the cornea occurs over time. Otherwise, poor
results would turn up in LASIK.