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.