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Advanced Surface
Ablation
KHADER FARWAN
How the eye works
• Light rays enter the eye through
the clear cornea, pupil and lens.
• These light rays are focused
directly onto the retina, the lightsensitive tissue lining the back of
the eye.
• The retina converts light rays into
impulses, sent through the optic
nerve to your brain, where they
are recognized as images.
• 70% of the eye's focusing power
comes from the cornea and 30%
from the lens.
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Refractive errors: myopia
• The distance between the cornea and the retina may be too long or
the power of the cornea and the lens may be too strong.
• Four types of refractive error:
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Myopia (nearsightedness)
Hyperopia (farsightedness)
Astigmatism
Presbyopia
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Refractive errors: myopia
• In myopia (nearsightedness),
there is too much optical
power in the eye.
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The distance between the
cornea and the retina may be
too long or the power of the
cornea and the lens may be too
strong.
Myopia, or nearsightedness
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Refractive errors: hyperopia
• In hyperopia (farsightedness),
there is too little optical power.
• The distance between the cornea
and the retina may be too short.
• Light rays are focused behind the
retina instead of on it.
• In adults (but not children),
distant objects will look clear, but
close objects will appear blurred.
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Hyperopia, or farsightedness
Refractive errors: astigmatism
• In astigmatism, the cornea is
curved unevenly—shaped more
like a football than a basketball.
• Light passing through the
uneven cornea is focused in
two or more locations.
• Distant and close objects may
appear blurry.
Astigmatism occurs when light
passes through uneven cornea
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Refractive errors: presbyopia
• Presbyopia is a normal
condition in which your eyes
gradually lose the ability to
focus things up close.
• When we are young, the lens in
our eyes is flexible and is able
to change focus easily between
near and far objects, like an
autofocus on a camera.
• At around age 40, this flexibility
naturally begins to gradually
decrease, making it more
difficult to see objects up close.
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What is refractive surgery?
• A group of outpatient surgical procedures used to alter how your
eye focuses light rays on the retina, thereby improving vision and
reducing dependence on glasses and contact lenses.
• In most cases, refractive surgery affects the shape of your cornea
to redirect how light is focused onto the retina. Popular
procedures include LASIK, LASEK, PRK and CK.
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What is refractive surgery?
• Most refractive surgery is performed on the cornea and affects
only the front of your eye, while the rest of your eye will change
naturally as you age.
• In some cases, refractive surgery procedures don’t reshape the
cornea; instead, the eye’s natural lens is either replaced or
enhanced by an implantable lens that helps correct vision.
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What is Advanced Surface Ablation (ASA)?
• A refractive surgery procedure where the outermost layer of the
cornea, the epithelium, is removed or displaced to expose the
stroma (the middle, thickest layer of tissue in the cornea).
• A computer-controlled excimer laser then reshapes the front
surface of the corneal stroma.
The outermost layer of
the cornea, the
epithelium, lies on top
of the stroma
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What is Advanced Surface Ablation (ASA)?
• The epithelium is either replaced or assisted in healing back over
the surface of the cornea underneath a bandage contact lens.
• Types of ASA: Photorefractive Keratectomy (PRK) and Laser
Epithelial Keratomileusis (LASEK).
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What is Photorefractive Keratectomy (PRK)?
• Outpatient refractive surgery used to treat nearsightedness
(myopia), farsightedness (hyperopia) and astigmatism.
• PRK involves:
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Manually removing the corneal epithelium.
Using an excimer laser to precisely sculpt the stroma according to the
specific refractive error to be treated.
Covering the cornea with a bandage contact lens to facilitate healing of the
epithelium.
• The goal of PRK is to focus light rays more precisely on the retina
to improve uncorrected vision.
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What is PRK?
• To treat myopia, the surgeon uses the laser to flatten the corneal
surface in a lenticular (lens-like) pattern.
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By reducing the curvature of the cornea, the eye’s focusing power is
decreased.
Images that are focused in front of the retina are pushed closer to or directly
onto the retina, producing clearer uncorrected vision.
With myopia, the laser is used to
flatten the corneal surface
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What is PRK?
• To treat hyperopia, the surgeon uses the laser to steepen the
cornea by removing tissue from the periphery of the cornea.
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By steepening the cornea, the focusing ability of the cornea is changed,
thereby adding refractive power to focus the incoming images more directly
on the retina instead of behind it.
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What is PRK?
• To treat astigmatism, the laser is programmed to selectively
reshape specific portions of the cornea more than others.
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The laser flattens areas that are steeper than normal and steepens areas
that are flatter than normal, usually in an elliptical pattern.
Allows the surgeon to deliver the correct amount of laser energy to the
appropriate areas of the cornea, thereby improving uncorrected vision.
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How is PRK performed?
• In addition to a complete pre-operative
eye exam, measurements are taken to
give the surgeon the necessary
information to perform the procedure:
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Refractive error measurement.
Pupil evaluation and measurement.
Tonometry: measurement of your eye’s
intraocular pressure (fluid pressure inside
your eye).
Corneal topography: mapping the surface
details of the cornea.
Keratometry: measurement of the form and
curvature of the cornea.
Pachymetry: measurement of corneal
thickness.
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A phoropter is used to
measure refractive errors
How is PRK performed?
• Anesthetic eyedrops are applied
to your eye(s).
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The non-treated eye is patched.
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How is PRK performed?
• A lid speculum is placed to
keep the eyelids open during
the procedure.
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How is PRK performed?
• The epithelium is removed
using an Amoils brush or by
using the laser itself.
An Amoils brush is used to
remove the epithelium
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How is PRK performed?
• An excimer laser controlled by a computer is programmed to
reshape the cornea, depending on the amount and type of
correction desired.
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The laser sculpts an area six to nine millimeters in diameter on the surface
of the eye, depending on whether the laser is correcting for myopia or
hyperopia.
The depth of the sculpting depends on the degree of correction needed.
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How is PRK performed?
• The laser removes tissue from
the cornea, either decreasing
the steepness of curvature for
nearsightedness or increasing
the steepness of curvature for
farsightedness.
With myopia, the laser is used in a
central, circular pattern
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How is PRK performed?
• After the procedure, a transparent bandage contact lens is placed
over the cornea to promote healing…
…and postoperative eyedrops
are applied.
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Considerations for PRK surgery
• May be recommended for people with lower levels of myopia or
hyperopia, although it is FDA approved to treat between -12 to +6
diopters of refractive error.
• May be recommended for people with thin corneas who would not
be good candidates for LASIK.
• May be recommended for people with dry eyes.
• Because a stromal flap is not created in the cornea (as with
LASIK), less corneal tissue is disturbed, therefore some surgeons
consider PRK to be a safer procedure than LASIK.
• Certain occupational restrictions against other forms of refractive
surgery (i.e., LASIK).
• Less invasive procedure than intraocular surgery, thus reducing
quality-of-vision complaints.
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Considerations against PRK surgery
• Slower visual recovery than LASIK or phakic IOL surgery.
• Not recommended for people with significant ocular disease of any
type, especially corneal disease.
• Not recommended for people with significant skin or systemic
disease that could adversely affect healing.
• Not recommended for people with a history of excessive scarring
when skin is broken.
• Not recommended for people with unstable or changing refractive
error.
• Some discomfort immediately following surgery, lasting for 2 to 3
days, occasionally requiring narcotics or topical anesthetics for
pain control.
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Risks and possible side effects of PRK surgery
• Over-correction or under-correction (with a possible need for a retreatment).
• Vision may be blurry for a few days up to several weeks, with the
achievement of best vision taking up to a month or longer.
• Glare and halos around lights, particularly at night.
• Corneal scarring and corneal haze.
• Corneal infection.
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What is Laser Epithelial
Keratomileusis (LASEK)?
• Outpatient refractive surgery useful in correcting nearsightedness
(myopia), farsightedness (hyperopia) and astigmatism.
• LASEK involves:
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Temporarily displacing the corneal epithelium using dilute alcohol.
Using an excimer laser to precisely sculpt the stroma according to the
specific refractive error to be treated.
Replacing the epithelium and using a bandage contact lens to speed healing
and reduce discomfort.
• The goal of LASEK is to focus light rays more precisely on the
retina to improve uncorrected vision.
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How is LASEK performed?
• As with other procedures, pre-operative measurements are taken
of your eye.
• A special alcohol solution is used to loosen the epithelium…
…which allows it to be peeled
back from the cornea.
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How is LASEK performed?
• Once the epithelium is displaced, an excimer laser controlled by a
computer is programmed to reshape your cornea.
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How is LASEK performed?
The laser removes tissue, either
decreasing the curve of your cornea
to correct nearsightedness or
increasing the curve of your cornea
to correct farsightedness.
After the laser treatment, the
epithelium is smoothed back into
position over the cornea, and a
bandage contact lens is placed
to promote healing.
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How is LASEK performed?
• The reshaped cornea focuses light more accurately on the retina.
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Considerations for LASEK surgery
• May be recommended for people with lower levels of myopia or hyperopia.
• May be recommended for people with thin corneas who would not be
good candidates for LASIK.
• May be recommended for people with dry eyes.
• Because a stromal flap is not created in the cornea (as with LASIK), less
corneal tissue is disturbed, therefore some surgeons consider LASEK to
be a safer procedure than LASIK.
• Certain occupational restrictions against other forms of refractive surgery
(i.e., LASIK).
• May be less painful during healing than PRK.
• May offer faster visual recovery than PRK (but not as fast as LASIK).
• Less invasive procedure than intraocular surgery, thus reducing qualityof-vision complaints.
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Considerations against LASEK
surgery
• Slower visual recovery than LASIK or phakic IOL surgery.
• Not recommended for people with significant ocular disease of any
type, especially corneal disease.
• Not recommended for people with significant skin or systemic
disease that could adversely affect healing.
• Not recommended for people with a history of excessive scarring
when skin is broken.
• Not recommended for people with unstable or changing refractive
error.
• Not recommended for people with myopia, hyperopia or
astigmatism beyond the range of PRK.
• Some discomfort immediately following surgery, lasting for 2 to 3
days, sometimes requiring narcotics or topical anesthetics for pain
control.
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Risks and possible side effects of LASEK surgery
• Over-correction or under-correction (with a possible need for a retreatment).
• Vision may be blurry for a few days up to several weeks, with the
achievement of best vision taking up to a month or longer.
• Glare and halos around lights, particularly at night.
• Corneal scarring and corneal haze.
• Corneal infection.
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Is refractive surgery right for you?
• New surgical procedures, including PRK and LASEK, are creating
more opportunities for people who want to be less dependent on
glasses or contacts.
• Surgery may not entirely eliminate your need for corrective lenses.
Glasses/contacts may still be needed for activities such as fine or
detailed work, reading and perhaps night driving.
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Is refractive surgery right for you?
• A large part of the success of any refractive surgery depends on
your understanding of the procedure and your expectations.
• Since refractive surgery is an elective procedure, you have the
opportunity and responsibility to become fully informed about its
risks and benefits.
• Your ophthalmologist will explain the specific technique, its
benefits, as well as possible risks and side effects associated with
your case.
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Discuss options and questions with
your ophthalmologist
• With the help of your ophthalmologist, it’s ultimately your
responsibility to weigh the risks and side effects of a procedure
with the benefits it has to offer.
• If you decide refractive surgery is right for you, you may join
millions of people who have reduced their dependence on glasses
or contacts.
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