Contact Lenses

Lens Fitting After Refractive Surgery

Bruce Koffler, MD
Lexington, Ky.

Contact lenses may help with developing presbyopia or an unsatisfactory surgical outcome.

AS THE NUMBER OF LASIK PROCEDURES performed in the United States continues to grow, so will the number of refractive surgery patients in need of contact lenses. Whatever the procedure, those who attained a good visual result may need lenses for presbyopia or to enhance visual performance, especially for nighttime driving. For patients with unsatisfactory results, contact lenses may be their best option for visual improvement.

This article will identify those patients whom contact lenses can benefit and describe how to select and fit the best lens for them.

Who Needs Lenses?

Poor visual outcomes after refractive surgery include under- and overcorrections resulting in residual myopia or progressive hyperopia, both of which may be associated with regular or irregular astigmatism. Patients who underwent radial keratotomy form the majority of my post-refractive surgery contact lens patients.

The 10-year report of the Prospaective Evaluation of Radial Keratotomy Study showed that 23 percent of patients had overcorrections or induced hyperopia greater than 1 D and 17 percent had undercorrections of residual myopia greater than 1 D.1 PRK and LASIK patients, by contrast, require contact lenses less frequently due to the greater predictability and accuracy of these techniques, but complications still occur.2

Other RK complications include nighttime halos and starbursting, irregular astigmatism, fluctuation in vision and invasion of the optical axis by the incisions. Similar symptoms occur less commonly after LASIK.

Case 1
Preop keratometry 46.50/47.87 @ 85š
Postop keratometry 39.00/39.50, irregular mires
Preop Rx -6.25 -2.50 @ 175š
Postop Rx +2.50 -1.25 @ 20š
Initial base curve 7.30 mm (46.25 D)
Power -4.25 D
Overall diameter 9.5 mm
Overall optical zone 8.0 mm
Intermediary curve radius 8.5 mm
Intermediary curve width 0.35 mm
Peripheral curve radius 12.25 mm
Peripheral curve width 0.4 mm

The base curve selection of spherical RGP lenses is near the flat K of the preoperative keratometry measurement. The lens should align over the mid-periphery and vault the central optical zone. Choose large lens diameters to aid lens centration.

Fitting Tips

I begin with a thorough history and physical and a slit-lamp examination of the eye and ocular surface. I also discuss the potential contact-lens complications unique to post-refractive surgery eyes and the goals for the fitting. The former include decentration and limbal impingement with neovascularization. Discussing goals may take more time than it does with other contact lens patients, as many people undergo refractive surgery in order to rid themselves of glasses or contact lenses.

• Timing. The patient's eye must be comfortable and the patient psychologically ready to use a contact lens. Healing must be complete, and you should be able to reproduce the refraction on multiple, successive attempts. Corneal thickness should be stable, and corneal sensation should be back at preoperative levels.

You may fit soft lenses in RK and LASIK patients as early as four to six weeks postop, but it's best to wait three months to fit a rigid gas permeable lens so that the flap's integrity is sufficient to withstand the trauma and movement of the lens. For high myopes, you'll often need to wait more than six months for the refraction to stabilize.

• Corneal topography. Software programs designed for normal spherical corneas aren't helpful in the post-refractive surgery patient, whose cornea is oblate in shape vs. the prolate shape of the normal cornea. Instead of being steep centrally and flattening to the periphery, these patients' corneas have a large, central, flat area that steepens in the mid-periphery and flattens again at the limbus.

Corneal topography helps determine, not just corneal shape, but also the optical zone size, simulated central keratometry, mid-peripheral corneal curvature and the diopter curvature change across the surgical transition zones. By using the cursor on a topography machine, you can ascertain the curvature power at any distance from the center.3 You can also use a keratometer to obtain peripheral keratometry readings.4

Lens Selection

• Lens material. RGP lenses are ideal for RK and LASIK patients, because there's a broad selection of high oxygen permeable plastics with the material stability, rigidity and hardness to allow for optimal visual performance. These lens materials have high oxygen transmissibility and permit efficient tear exchange, which removes tear debris and corneal byproducts. The formation of a posterior lens tear pool, meanwhile, neutralizes any corneal irregularity and thereby optimizes visual performance. Drawbacks of RGP materials relate to comfort, centration and the ability of the lens to stay on the cornea.

RK patients done with older techniques and who have incisions to or through the limbus need RGP contact lenses. Soft lenses that impinge and rub at the limbus will produce neovascularization into the RK scars and eventually cause hemorrhaging and additional scarring. Patients who had newer RK techniques that used mini-incisions may receive either RGP or soft lenses with a high Dk/L, since there's a definite 2- to 3-mm clear zone between the limbus and the peripheral edge of the incision. LASIK and automated lamellar keratoplasty patients may also use either RGP or soft lenses.

• Spherical RGP lenses. Base curve selection is near the flat K of the preop keratometry measurement (See Case 1). For example, if the preop Ks are 45.00 x 47.00, fit a 45.00 base curve initially. This reading may be 3-6 D steeper than the postop Ks. The lens should align over the mid-periphery and vault the central optical zone. If there's an air bubble, flatten the base curve in 0.5-D steps until the air is gone. To center the lens, opt for large diameters from 9.5 to 11 mm. Also, use large optical zones around 8 mm.

Case 2
Postop refraction -2.25 -1.25 @ 155š
Postop Ks 41.50 sphere
Initial fit -0.25 D/39.50 BC/ 10.2/8.2 Oz
Base curve selected 39.50 D

We can attempt to reshape the post-refractive surgery cornea and improve the final refraction via reverse geometry lenses. This 51-year-old female post-RK patient had a residual myopic correction. In an attempt to reduce the -2 D of residual correction, I selected a base curve 2 D flatter. I found a 1:1 ratio between a dioptric flattening of the base curve and the dioptric power change of the refraction.

Be sure to maintain 2.0 mm for transition curves with the intermediate curve 1 mm flatter than the central base curve. For the peripheral curve, use a standard radius of 12.25 mm and a width of 0.4 mm. This will provide plenty of edge lift to facilitate tear flow underneath the lens. Determine the power by refracting over a diagnostic lens. Adjust the base curve and lens diameter according to a fluorescein evaluation, lens movement and lens centration.5 High oxygen fluorosilicone acrylate materials ensure maximal oxygen transmission.

• Custom lenses. Reverse geometry lenses have become popular for patients who can't be adequately fit with standard RGP designs. They feature secondary curves 3-6 D steeper than central curvatures and are commonly used to maintain alignment along a plateau-shaped cornea. They prevent excessive tear pooling and lens bearing and provide better fitting stability and centration. In addition, these lenses enable us to attempt the reshaping of the post-refractive surgery cornea. For instance, by flattening the cornea of an RK patient who has residual myopia despite an enhancement procedure, we may be able to improve the final refraction (See Case 2).

I've used the Lexington RK Splint multicurve contact lens design (Aero Contact Lens of Ohio, West Carrollton, Ohio, 1 (888) 866-9400), which most labs can make in a plateau shape.6,7 It has a central base curve and four peripheral curves, a design that simulates the aspheric shape of a normal peripheral cornea. Another option is the NRK lens (Lancaster Contact Lens Lab, Lancaster, Pa., (717) 569-7386), which was created for the plateau-shaped cornea. The Menicon Plateau lens (Con-Cise Contact Lens, San Leandro, Calif., 1 (800) 772-3911), meanwhile, features a central base curve and three peripheral curves.

Another popular choice for irregular corneas is the MacroLens Contact Lens (C&H Contact Lens, Dallas, 1 (800) 527-5060). These lenses use a high Dk/L material and feature a laser hole to facilitate the exchange of tears, oxygen and residual air bubbles. Patients tend to find these lenses comfortable and the vision they provide excellent. They're stable on the eye, center well and don't have any significant degree of movement.

• Soft lenses. Spherical and toric soft lenses can work well, particularly in LASIK patients, because the changes in their mid-peripheral corneal shape aren't as abrupt as those of RK patients. These lenses are often ideal for patients with small, residual refractive errors and may help correct irregular astigmatism. Because the limbus is untouched, soft lenses are far less likely to cause neovascularization in these patients.

One potential problem relates to the oblate shape of the cornea. When the wearer blinks, the lens may buckle or flex and become aberrated. Several sp ecialty soft lenses resolve this problem. The bicurve design of the SoftPerm lens (Wesley Jessen/CIBA Vision) features a central gas permeable lens joined with a soft contact lens skirt. Another option is the Flexlens PRS Lens (X-Cel Contacts, Atlanta, 1 (800) 241-9312), which is designed specifically for patients whose corneal topography was altered after RK, PRK or LASIK. It functions like a reverse geometry design that incorporates a central optic portion that's flatter than the mid-periphery.

I use the Flexlens Piggyback Lens (X-Cel Contacts) as a last resort in patients who can't be fit with other lenses due to poor centration. The piggyback design requires a special patient who has good hand-eye coordination and can place the RGP lens into the groove created in the soft contact lens.

Instead of eliminating lens wearers, refractive surgery has created patients with new contact-lens needs. RO

Dr. Koffler is medical director of the Kentucky Center for Vision in Lexington. He is president-elect of the Contact Lens Association of Ophthalmologists.

1. Waring GO III, Lynn MJ, McDonnell PJ, et al. Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery. Arch Ophthalmol 1994;112:1298-308.

2. Danasoury MA, et al. Excimer laser in situ keratomileusis to correct compound myopic astigmatism. J Refract Surg 1997; 23:372-85.

3. Szczotka LB, Aronsky M. Contact lenses after LASIK. J Am Optom Assoc 1998;69:775-84.

4. Campbell MD, Caroline P. A unique technique for fitting post RK patient. Contact Lens Spectrum 1994;12:56.

5. Ward MA. Contact lens management after refractive surgery. Contact Lens Spectrum 1996;October:23-30.

6. Koffler BH, Clements LD, Literal GL, Smith VE. A new contact lens design for post-keratoplasty patients. CLAO J 1994;20:3:170.

7. Koffler BH, Smith VM, Clements LD. Achieving additional myopic correction in undercorrected radial keratotomy eyes using the Lexington RK Splint design. CLAO J 1999;25:1:21-7.