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After Lasik and similar laser eye surgery, patients sometimes experience
temporary problems with focusing, perception of distances, eye strain,
headaches, fatigue, vertigo, even nausea and dizziness. These normally
temporary symptoms may be related to the sudden change of optics
created by Lasik or Lasik dry eye.
An issue often related to these symptoms is Lasik
dry eye.
When the eye is in a relaxed state, it is myopic (nearsighted, shortsighted), hyperopic (farsighted, longsighted), or emmetropic (no refractive error). When emmetropic, the optimum depth
of focus is about 20 feet and beyond.
A complicating factor to these optic states is astigmatism. Astigmatism most often refers to the cornea not
being spherical like the top of a ball, but being elliptical like
the back of a spoon. Astigmatism would cause some - but not all
- light passing through the cornea to be focused off-center. For
purposes of discussion we will assume there is no astigmatism.
Accommodation and Convergence
Accommodation is when the natural crystalline lens in the eye changes shape to manipulate the
focus of light entering the eye. Accommodation dynamically changes
the optic state of the eye. As an example, if an emmetropic patient
wanted to see an object within about 20 feet, the natural lens would
change shape to make the patient myopic, thus allowing clear focus
on a near object. If a person was myopic and wanted to see an object
more than about 20 feet away, the natural lens would change shape
to make the patient plano.
Up to about age 40 we have a significant amount of accommodation.
An often overlooked part of seeing objects near is convergence.
When looking at a distant object, the dominant
eye looks directly at the object and the nondominant eye looks
at the object from a slight angle. This difference between straight
on and slight angle helps provide depth perception. When looking at an object near, the eyes converge
toward each other to keep the relative angles of the dominant and
nondominant eye the same as with distance and provide good depth
perception. This convergence, which can look like a person is cross-eyed,
is performed with the muscles outside the eye that control eye direction.
Presbyopia is when the natural lens of the eye becomes less
able to change focus. Presbyopia is a natural part of the aging
process that actually starts at around age 8-10, but is not very
noticeable until around age 40 when it becomes difficult to read
a newspaper and otherwise see objects close. This is when we need
reading glasses or bifocals.
It is important to remember that there are two ways to describe
myopia. One is that you cannot see things far away very well, the
other is that you can see things close very well. Reading glasses
are actually regular spectacles designed to make the wearer more
myopic. If you are naturally myopic and presbyopic, it is probably
possible to just remove your glasses to see objects near. Even with
glasses on, myopia provides a mechanical advantage and can “mask”
the effects of presbyopia.
If you have Lasik or similar refractive surgery and remove your
myopia, you remove any advantage that myopia provided for near vision
and are suddenly hit with the full effects of presbyopia. We call
this “sudden
presbyopia” and it catches Lasik patients in their early 40’s
off guard all too often. Before surgery seeing things close was
not much of a problem, now they need reading glasses to see objects
near.
In addition to removing any advantage myopia may have provided,
refractive surgery changes the range of accommodation and convergence
necessary to see objects near. For the sake of demonstration (and
these numbers are only for demonstration) let's say that
the range of focus of your eyes is 1-10. The range 1-3 is for near
focus, like your computer. Range 4-7 is for mid-range, like your
TV, and 8-10 is for distance vision. In the 8-10 range your eyes
are almost or totally relaxed with no accommodation and no convergence.
To achieve clear vision in the 4-7 range, you must accommodate.
To achieve clear vision in the 1-3 range, you must accommodate and
converge.
Before surgery, myopia provided a mechanical advantage (gross
over-simplification but you get the idea) for the 1-3 range. You
actually had to accommodate and converge less before surgery than
after. Before surgery your myopia would have provided a slight advantage
in the 4-7 range. Not much, but a little. Now that you don't have
myopia, your accommodation and convergence must work full time,
not part time.
If you have been overcorrected into hyperopia, your range is
now -3 to 10 and your eyes must first accommodate an additional
3 steps.
All this attempted accommodation and convergence can cause more
than just poor vision. Accommodation and convergence deficiency
can cause headaches, nausea, vertigo, and dizziness.
Since we are going into great detail, let’s throw in anther complicating
matter. If one eye does not have the same refractive error - especially
if one eye is hyperopic and the other is myopic - then the accommodation
and convergence is imbalanced and one eye is always working harder
than the other. Also, the size of the images hitting the retinas
may be different, causing the eyes to be constantly trying to focus
away the resulting blur.
All of these issues may combine into the “perfect storm” to cause
problems with focusing, perception of distances, eye strain, headaches,
vertigo, nausea, and/or dizziness. If you are experiencing these
problems after Lasik or similar surgery, there are some options
you may consider. What is most appropriate will depend upon the
exact nature of the problem.
If the refractive error is different between the two eyes, contact
lenses, glasses, or enhancement surgery to provide full and balanced
correction may be the appropriate solution. If the issue is accommodation
and convergence, the brain and eyes tend to become acclimated to
the new range of vision correction with enough time.
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.
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