Contact Lens Business
Fitting Keratoconus Patients
Guidelines for diagnosing this condition and choosing the most effective contact lenses.

BY WILLIAM H. CONSTAD, M.D.

Fitting keratoconus patients with contact lenses can be a challenge. How-ever, if you take a rational, stepwise ap-proach to the fitting process, you should be able to fit even problematic patients.

Here are some helpful strategies I've learned during many years of working with these patients.

MAKING THE DIAGNOSIS

Diagnosis can be difficult in the early stages of keratoconus. As the cone forms, it generally first causes a regular type of astigmatism that can be corrected with glasses or soft toric contact lenses. As it progresses, however, the astigmatism becomes irregular.

On examination, you may find:

• scissoring of the retinoscopic reflex
• a doubling of the mires on the keratometer
• the major and minor keratometer axes less than 90° apart.

These changes can be difficult to observe, although corneal topography will often pick them up.

CHOOSING THE RIGHT LENS

In early keratoconus, patients can wear soft contact lenses. If the two principal meridians are 90° apart, soft toric lenses may provide excellent vision. If soft torics aren't adequate, consider:

• standard rigid gas permeable (RGP) lenses
• specialty RGPs with multiple posterior radii to accommodate the distorted anterior corneal surface
• combination lenses (such as the SoftPerm lens from CIBA Vision)
• piggyback lenses (i.e., an RGP on top of a soft lens).

To help you decide which lens to fit, start with topography. Look at the size and position of the cone. If the cone is central, not too large, and not too steep centrally (less than 60D), a standard RGP will probably work well. If the cone is significantly off-center or steeper than 60D at its apex, the patient will probably need to wear a specialty lens.

FITTING THE CONE

Fitting a centered cone (where the visual axis of the cornea corresponds with the apex of the cone) with a relatively small diameter RGP lens is called "cap fitting." Generally, you can attain a very good anatomic fit using this technique. The challenge is avoiding a lens that pops out too easily or is too uncomfortable because of lid sensation.

To fit other types of cones, such as decentered or sagging cones, you need to have a lens that will span over the cone, touching at the apex and the periphery. This is referred to as a "three-point touch." (See illustration, below, left.) You may be able to achieve this type of fit with a standard RGP lens, but often, if the cone is pronounced, decentered or irregular, you'll need a specialty lens.

A number of specialty lenses designed for this purpose are available. (You'll need a fitting set for each type you use. Order your fitting set from the lab that will make the lenses.)

One specialty lens, the Soper Cone lens, has two principal base curves: a steeper central curve and a shallower peripheral curve. To order it, you'll need to specify four measurements: the central curve, the diameter of the central section (referred to as the "cone diameter"), the peripheral curve, and the overall lens diameter. The cone is available in three diameters: 6.0, 7.0 and 8.0 mm. The overall lens diameter ranges from 7.0 mm to whatever you need.

A "three-point touch" keratoconus fit using a standard RGP lens (top) and Soper Cone lens (bottom).

This lens works well for more advanced cones, and keeps the three-point fit (see illustration, left).

DUAL-MATERIAL LENSES

Another specialty lens, the SoftPerm from CIBA Vision, has a central RGP portion surrounded by a skirt of hydrophilic material. It's available in standard base curves from 7.1D to 8.0D in 0.1D increments, as well as 6.5, 6.7 and 6.9D base curves for keratoconic patients. (The diameter is fixed at 14.3 mm.) These lenses need to be fit so that they move as little as possible on the eye. Note: As these lenses are worn they may become a little tighter. Have the patient wear the lens in your office for 20 or 30 minutes to be sure the fit is correct.

The big advantage of this lens is that it's much more comfortable because the periphery of the lens is soft. The soft skirt also stabilizes the central RGP region, which helps to keep vision from changing too much when the patient blinks.

While these can be marvelous lenses, they have drawbacks: If the lens isn't handled carefully, it can separate at the junction between the RGP center and the soft skirt. The company has also had recent difficulties with its sterilization and manufacturing process, and the lens has been unavailable since August, 2001. However, they've recently begun to ship some of the back-ordered lenses.

CIBA Vision offers an unconditional 3-month warranty with this lens.

CHALLENGES AND REWARDS

Fitting a keratoconus patient with lenses does require more chair time than fitting a patient who needs only standard or toric soft lenses. And the process is more complex; you may need to adjust a lens or exchange it during the fitting process. (It's important to check with your lab about its specific exchange or replacement policies.)

Nevertheless, helping these patients achieve good vision can make a big difference in their lives and generate tremendous good will for your practice. And that's an outcome everyone can appreciate.

Dr. Constad is in private group practice with Hudson Eye Physicians and Surgeons in Jersey City, N.J., and is clinical associate professor in the Department of Ophthalmology at the University of Medicine and Dentistry of New Jersey. He completed a fellowship in cornea and external disease with Jorge Buxton, M.D., at the New York Eye and Ear Infirmary in 1985.