|Astigmatism means the cornea is not spherical, like the
top of a ball, but is elliptical, like the back of a spoon.
Astigmatism is a corneal irregularity that causes multiple
focal points and distorts vision.
Conventional or custom wavefront Lasik, Bladeless Lasik, PRK, LASEK,and Epi-Lasik, can correct astigmatism. Most refractive surgeons consider it much more
difficult to correct astigmatism than myopia (nearsighted, shortsighted) or hyperopia (farsighted, longsighted). As a very general rule,
if your astigmatism is more than half your sphere, then the probably
of a good outcome is diminished. If your astigmatism is more than
2.00 diopters, your probably of a good outcome is significantly diminished.
Lens Based Limitations
Lens based refractive surgery procedures like P-IOL and RLE do not correct astigmatism well, however RLE can correct lenticular astigmatism. Although toric intraocular lenses (IOL) are available, placement and rotation
issues make astigmatic correction difficult.
The amount and type of astigmatism that can be corrected will
depend upon many factors. Lasers are approved by the FDA for specific levels of astigmatic correction. More than the laser, the physiological features of your eye will
determine if your astigmatism can be corrected with refractive surgery.
Issues such as thickness of cornea, pupil size, plus type and amount of astigmatism will all be
Indirectly Correct Astigmatism
P-IOL, and RLE do not directly correct astigmatism, however a minor amount
of astigmatism can be corrected as a part of the surgical process
of correcting myopia or hyperopia.
P-IOLs available in the US do not correct astigmatism, but the incision
through which the P-IOL is placed inside the eye can be manipulated
to reduce preexisting astigmatism. Equally, the incision created
during RLE through which the IOL is placed inside the eye can be manipulated to reduce preexisting
Laser Coupling Effect
Something important to remember is that with most laser assisted
astigmatic refractive surgery techniques, for each diopter of astigmatism
that is corrected, a certain amount of myopia is also automatically
corrected - even if you don't need the myopia correction.
This coupling of myopic correction and astigmatic correction is
consistent with virtually all excimer lasers.
As an example, let us assume that for every one diopter of astigmatic
correction the technique also corrects 0.25 diopter of myopia. If
you have 2.00 diopters of astigmatism, you will receive 0.50 diopters
of myopia correction (0.25 diopters of automatic myopia correction
multiplied by the 2.00 diopters of astigmatism to be corrected)
even if you do not need the myopia correction. If you have more
than 0.50 diopters of myopia, a 2.00 diopter astigmatic correction
should not be a problem with this technique. If you are plano then after surgery you would be 0.50 diopters hyperopic
- not a desirable outcome.
Different Astigmatism Types
Irregular astigmatism is very, very difficult to correct and
some techniques and technology cannot fully correct an irregular
astigmatism at this time. Every person with irregular astigmatism
is unique and needs to be individually evaluated.
Lenticular astigmatism is when the irregularity is in the natural
crystalline lens, rather than in the cornea. RLE will eliminate
lenticular astigmatism. Cornea-based surgery techniques conventional
and wavefront Lasik, Bladeless Lasik, PRK, LASEK, and Epi-Lasik
can correct lenticular astigmatism's effects, but making a reverse
of the lenticular astigmatism in the cornea. While this can be a
successful technique of lenticular astigmatism correction, there
is a significant concern.
As we age the natural lens of the eye becomes clouded. This is
called a cataract. The process to resolve a cataract is to remove
the natural lens and replace it with an artificial lens. The problem
is that the artificial lens will not have the pre-existing lenticular
astigmatism and if the cornea has been reshaped to accommodate the
lenticular astigmatism, the cornea will now cause an irregular astigmatism.
Discuss in detail with your doctor the type and amount of astigmatism
you have and how it may be accommodated with refractive surgery.
Discuss if the technology and techniques s/he intends to use may
affect myopic correction and how this may be accommodated for your
Looking For Best Lasik Surgeon?
If you are ready to choose a doctor to be evaluated for conventional
or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization.
Locate a USAEyes Evaluated & Certified Lasik Doctor.
If this article did not fully answer your questions, use our
free Ask Lasik Expert patient forum.