Although
laser-assisted in situ keratomileusis (LASIK) patients often have excellent
surgical results, the sheer size of the group guarantees that a significant
number of patients will be either over- or undercorrected and possibly have
induced astigmatism. In addition, many LASIK patients need contact lenses to
compensate for presbyopia, or to use in specific situations (e.g., night
driving).
In our
practice, we also fit many post radial keratotomy (RK) patients. A study of RK
patients 10 years after surgery, conducted by Waring, et al., in the early
1990s, found that 40% of these patients had residual hyperopia or myopia greater
than 1D.
In
addition, complications may include visual fluctuation during the course of the
day (due to changes in corneal hydration), irregular astigmatism, uneven
healing, scarring, and halos or sunbursts at night.
The
contact lens solution
If a
patient isn't willing to tolerate these problems, contact lenses can often help.
When fitting RK or LASIK patients, we generally follow six steps:
-
We
assess the problem by taking a history and performing a slit-lamp exam.
-
We
decide which type of lens is most appropriate for the patient.
-
We
discuss goals with the patient. Some patients will need extra chair time to
get accustomed to the idea of wearing lenses because avoiding lenses may
have been part of the motivation for having the surgery in the first place.
-
We
decide which fitting method is most likely to produce the best result.
-
We
proceed with the fitting and adjust
parameters until the lens fit is optimum.
-
We
follow these patients aggressively to ensure that we address complications
as soon as possible.
Timing
counts
For a
successful contact lens fit after surgery, I recommend waiting until:
-
the
healing process is complete
-
refractions
are consistent over time
-
corneal
thickness is stable
-
corneal
sensation has returned to pre-surgery levels
-
the
patient is psychologically ready to use a lens again.
Timing
also depends on whether the lens you've chosen is a soft lens or RGP:
-
RK
and LASIK patients can usually be fit with soft contact lenses as early as 4
to 6 weeks after surgery.
-
RGP
lenses probably shouldn't be used earlier than 3 months after surgery, to
allow the cornea sufficient healing time to withstand the trauma caused by
the movement of a rigid lens. (In high myopes, you may want to wait 6
months, given the more extensive surgery.)
Determining
corneal curvature
Careful
measurement of corneal curvature is essential for these patients. In contrast to
the normal prolate corneal shape, refractive surgery usually produces an oblate
or plateau-shaped cornea: a large central flat area with steeper curvature in
the mid-periphery, flattening out again at the limbus.
Corneal
topography can help you determine optical zone size, simulated central
keratometry, mid-peripheral curvature and the diopter curvature change across
the surgical transition zones. (You can use the cursor on a topography machine
to find the curvature power at any point across the cornea.)
Also,
peripheral keratometry readings can be obtained using a technique described by
Campbell and Caroline. (See Contact Lens Spectrum, December, 1994.) They
place four fixation dots 4 mm from the horizontal and vertical edges of the
keratometer viewing port in a symmetrical pattern and have the patient fixate on
each one in turn. By taking a reading each time, nasal, temporal, superior and
inferior mid-peripheral readings can be obtained.
Next
month: The case for RGPs.
Dr.Koffler
is director of the Kentucky Center for Vision in Lexington, Ky., and associate
clinical professor of ophthalmology at the University of Kentucky Medical
Center. He currently serves on the board of directors of the Contact Lens
Association of Ophthalmologists, and is past president of the Kentucky Academy
of Eye Physicians and Surgeons.