A Guide to Prescribing Contact Lenses After Refractive Surgery

BY DAVID I. GEFFEN, O.D.
FEB. 1996

Surgical vision correction can take many forms, and when a patient needs contact lenses after surgery, the practitioner must be prepared.

Refined surgical techniques coupled with significant advances in laser technology have resulted in numerous options for vision correction. The availability of these options has also increased the likelihood that optometrists will be seeing more surgically altered corneas, adding a new dimension to prescribing contact lenses.

For the past two years, my colleagues and I have had the opportunity to prescribe contact lenses for most types of refractive surgery patients. Our practice was an investigational site for photorefractive keratectomy and our surgeons are experienced with RK, ALK and LASIK.

THE POST-PRK PATIENT

Now that photorefractive keratectomy has been approved by the FDA, it's only a matter of time before a patient who has undergone this procedure comes to you for help. Typically, patients who want contact lenses after PRK are slightly under-corrected and they may need contact lenses for sports or other part-time activities. Patients who choose monovision refractive surgery occasionally need a contact lens to improve distance acuity on the near eye.

First, don't panic. Fitting post-PRK patients is usually straightforward. On the plus side, the postsurgical cornea seems to be less sensitive and thus tolerates a contact lens better than an eye that has not had surgery.

PRK treats the central 6mm of the cornea. This zone is smaller than the average optic zone of most contact lenses. Therefore, when fitting contact lenses after PRK, you must realize that the central keratometry readings should be clear, but flatter than expected. Topography will help determine peripheral corneal readings as well as smoothness of the treatment and transition zones. Topography (Figs. 1 & 3) usually shows a very regular pattern with the central cornea flatter than normal.

FIG. 1: TWO PRE- AND POST-EXCIMER PATIENTS ON ABSOLUTE SCALE.	FIG. 2: PRE- AND POST-RK ON BOTH EYES, ABSOLUTE SCALE.
FIG. 3: EXCIMER DIFFERENCE SHOWING UNIFORM ABLATION AND RETAINED CYLINDER IN POST-OP.	FIG. 4: DIFFERENCE MAP OF PRE- AND POST-RK.PATIENT HISTORY CHECKLIST TO EVALUATE POST SURGERY PATIENTS FOR CONTACT LENSES

The nice surprise in fitting post-PRK patients is the fact that the peripheral cornea has not been changed. Unlike RK which can produce irregularities in the periphery, PRK does not change the corneal shape outside the treatment zone. Rarely will you see induced astigmatism. A patient who previously wore soft contact lenses can usually wear them postoperatively. Look for smooth movement of the soft lens without central bubbles. We have successfully prescribed disposable, conventional and even soft toric lenses to post-PRK patients.

Gas permeable lenses must ride on the intermediate cornea rather than central bearing. Aspheric designs provide excellent vision and comfort. Try to avoid excessive central clearance because this can make the lens seal off and cause physiological changes such as corneal edema and punctate keratitis. Good tear exchange is crucial for comfort. Although plateau or OK lenses are not necessary for these corneas, you can use them if you prefer.

The patient who has residual haze (Fig. 5) and decreased acuity as a result may benefit from gas permeable lenses. Most of my patients increase about two lines of acuity with gas permeable lenses versus spectacles when haze is a problem. This is a good treatment to help the patient through the period until haze clears.

Trial fitting is imperative with post-PRK patients. While corneal topography is a good starting point and may help you to understand the corneal contours, it's no substitute for an old-fashioned trial lens. With gas permeable lenses, I would encourage you to go 0.2mm steeper and flatter than your initial trial lens to help determine the optimum fit. I usually wait at least three months after PRK before prescribing contact lenses to allow the cornea sufficient time to heal and stabilize.

Infrequent complications of PRK include irregular astigmatism, decentered treatment zones and central islands. The latter may be caused by poor laser beam profiles. Gas permeable contact lenses will help improve acuity with these complications.

THE RK PATIENT

After radial keratotomy, the surface of the cornea is quite irregular. Centration is the most challenging aspect of fitting a post-RK cornea because there is essentially no good bearing zone on the cornea (Figs. 2 & 4). This is especially true of surgeries performed more than four years ago. Since then, the procedure has improved so that we're seeing fewer, shorter, smoother incisions.

Initially, we try an aspheric lens and test for stability. If the lens drops, we switch to a different base curve or a different lens design. Sometimes we use the OK-60 lens (a lens designed for orthokeratology) because it has a flat central zone with a steeper intermediate zone. For the post-RK cornea, these lenses center better.

We've also had some success with the Softperm lens, but you must be alert for neovascularization. These lenses are not very permeable, resulting in reduced tear flow and poor oxygen exchange.

Follow-up visits are usually more frequent for our postsurgical contact lens patients (one week post-dispensing, then two weeks later, then a month later), and we follow these patients longer. We usually see post-RK contact lens patients every six months.

On average, the soonest we see a post-RK patient for a contact lens consultation is six months after surgery. We generally wait until the cornea has had a greater chance to heal before we put a contact lens on it. However, a patient who was overcorrected may come in as soon as six weeks after surgery because a contact lens can sometimes help reverse the overcorrection.

ALK & LASIK

For automated lamellar keratoplasty (ALK), the surgeon uses a microkeratome to cut across the corneal cap. The cap is then flipped aside and the surgeon makes a second pass with the instrument calibrated for a specific corneal thickness. Although this procedure is not as widely accepted as other surgical techniques, ALK is often employed for prescriptions over -6.00D.

Because the surgeon uses metal blades, the inherent drawback of this procedure is its lack of precision, thus ALK patients may be left with irregular astigmatism. We usually use a gas permeable lens in either a standard spherical or aspheric design. We sometimes use an ortho-k lens to aid in the healing process for three or four weeks after surgery.

Laser in-situ keratomileusis or LASIK is gaining favor among refractive surgeons. Commonly called "flap and zap," the procedure involves making a single incision with a microkeratome to expose the corneal stroma, then ablating the stroma with an excimer laser and replacing the corneal flap. The major advantage with LASIK, is that the procedure is much more precise than RK and there are fewer chances of creating corneal irregularities. To date, our results with LASIK have been so good that we have not had a patient return to us for contact lens correction. In fact, 24 hours after surgery, patients often are seeing 20/40 or better.

PSYCHOLOGICAL ASPECTS

A patient's state of mind is an important factor to consider when evaluating a post-refractive surgery patient for contact lenses. Aside from a corneal defect or recurrent erosions, lack of patient motivation is the only significant contraindication for contact lens wear after surgery.

A patient who comes in within two years of surgery, generally is not happy that he needs contact lenses. He may have been an unsuccessful wearer prior to surgery, and the prospect of attempting contact lens wear again is not an attractive one. This situation requires your best patient management and communication skills.

SUMMARIZING YOUR OPTIONS

Although you must evaluate each case individually, here are some guidelines to keep in mind:

• PRK patients can easily wear almost any soft contact lens for monovision or residual refractive error as needed.
• RK and ALK patients (or the rare PRK patient with an irregular cornea) can benefit from rigid lenses. If common RGP spheres or aspherics fail, try bridge or OK designs.
• When evaluating an RK patient, use the original keratometry readings, not the current K's, as a starting point for base curve selection.
• Heed the patient's motivation to see well without devices.

MEETING THE CHALLENGE

Properly prescribing contact lenses for the post-refractive surgery patient is fast becoming an important asset for optometrists. With the large number of patients who will eventually undergo treatment, particularly PRK, we must understand the unique properties of the postsurgical cornea. This challenge is not difficult and with experience, I believe most practitioners will become proficient in fitting contact lenses for these patients. CLS

Add the following to your standard patient history when evaluating a post-refractive surgery patient for contact lenses:

• Take a thorough contact lens history, including:
  1. Type of lens(es) worn (brand, material);
  2. Previous wear schedule;
  3. Reasons for success/failure with previous contact lenses.
  
• Request the name of the patient's surgeon as well as the practitioner he saw before surgery. This is valuable in gathering further information about the patient's eye health, including pretreatment keratometry readings and contact lens or spectacle prescriptions.
  
• Determine the patient's motivation to wear contact lenses.
  
  

Dr. Geffen is in a group O.D./M.D. practice in San Diego, Calif. He joins Contact Lens Spectrum in 1996 as a contributing editor.