Do not overlook role of corneal topography in contact lens fitting

Issue: July 1998

--- Contact lens software from Tomey, as shown in this screen capture, uses global fitting rules for determining lens category and specific rules for designing the selected lens.

MADISON, Tenn. - Clinicians who want to fit more specialty contact lenses while increasing compliance and reducing chair time for these patients can use an instrument already at hand - a corneal topographer - to accomplish this goal.

So says Walter L. Choate Jr., OD, FAAO, a private practitioner here who specializes in contact lens fitting. "You cannot get into most specialty contact lens designs - bifocal, toric, post-refractive surgery or keratoconus - and do them nearly as efficiently without corneal topography," Dr. Choate told Primary Care Optometry News. "Not that you couldn't do them, but the chair time needed would make the procedures far more difficult. The software development is not at its peak yet, but it gets us very close to that final lens."

Getting close to the final lens is what makes today's topographers and contact lens software packages more valuable to contact lens fitters. "You still need to do trial fitting, but corneal topography gives us our best first trial lens to put on the eye. In most cases, that also shortens chair time," said Dr. Choate, who has had a corneal topographer in his practice for nearly 5 years.

Dr. Choate currently uses Alcon's Eyemap system and contact lens program. "Alcon's software program is very good," he said. "Corneal topography, in general, is invaluable. It makes rigid gas-permeable (RGP) lens fitting much simpler, and it positively affects your practice management by reinforcing proper lens wear to patients."

Dr. Choate performs corneal topography annually on each contact lens patient. "We feel it is important because we are measuring and analyzing corneal geometry, not just the central 2 to 3 mm of the cornea where you're only getting a power measurement," he said. Before he fits a contact lens patient for the first time, Dr. Choate performs baseline topography "to tell us where the patient is before we apply a lens to the eye."

From there, topography builds patient education by reinforcing his role as a contact lens fitter.

"When I have a picture on the computer screen showing patients what they are doing to their eyes, it reinforces what is wrong and what they must do to help comply with their follow-up care or replacement cycles," Dr. Choate said.

This is especially helpful with hydrogel lens and flexible-wear patients who wear their lenses overnight. "You can show people maps from 6 months ago vs. today and explain to them the corneal changes they see are from overwearing their lenses," Dr. Choate said.

After this, he said, it becomes easier to tell patients to stop wearing lenses over- night and have them return in 3 to 4 weeks for another mapping to see the difference.

The only disadvantage Dr. Choate sees with today's topography instruments is their size. "Sometimes, it is a question of whether or not the office can house the instrument," he said.

Contact lens fitting programs associated with today's topographers offer practitioners a default fitting philosophy that can be easily modified to reflect individual preferences, said Anne Moskowitz, OD, PhD, director of clinical support at Tomey Corporation. In addition, the fitting rules for each lens in the database may be individually modified. "Our program, for example, automatically selects the appropriate lens category using global fitting rules, then chooses a specific lens based on the user's preference," she said.

Tomey's lens fitting program allows clinicians to modify all parameters and instantly see the fluorescein pattern, Dr. Moskowitz said, as well as reposition, rotate and/or tilt the lens. "This software can be used at any level," she said, "but clinical judgment is important and the clinician has to use expertise in determining whether or not the lens is a good fit."

Dr. Moskowitz lists several ways corneal topographers assist practitioners in improving or increasing contact lens fits in their practice. These include:

more complete data collection,
reduced chair time and
reduced patient discomfort.

"Our software uses the topography of the entire cornea," she said. "Data are acquired from approximately 8,000 points instead of only 4 points as in standard keratometry." Topography allows practitioners to choose an initial lens that is very close to the final fit, she said.

"This is particularly helpful in fitting atypical corneas," she said. "Also, the software makes the clinician's job easier by determining residual astigmatism, correcting contact lens power for vertex distance and computing lens power and axis when an over-refraction is entered."

In one educational setting, corneal topography has emerged as a learning tool for optometry students, said Christopher Snyder, OD, professor of optometry and chief of contact lens patient care at the University of Alabama at Birmingham. Dr. Snyder and his students use the Alcon Eyemap system.

"Our experience with this contact lens software is relatively short, but it is valuable to use it to demonstrate fluorescein patterns of rigid contact lenses," he said. The colorful images produced by topography help students visualize what the lens looks like and how it would change if certain parameters were modified.

Students ultimately learn how to use and interpret the results of corneal topography, Dr. Snyder said. "Topography gives you the static relationship of the contact lens to the corneal contour," he said, "but when you put a real contact lens on the eye, what it does is potentially different from the dynamics of what happens when the eyelids really drive that lens, push it down and center it."

Dr. Snyder advises students that "topography is a starting point, but if you really want to know what's going on, you have to go beyond that and do on-eye lens fitting."

Topographers have also proven valuable, he said, for troubleshooting to give students an idea of why a lens is not doing what they want.

From RGPs to soft torics

Jean Brandau, product manager for corneal topography products at EyeSys/Premier, said their contact lens fitting software was originally designed to fit RGP lenses, but the manufacturer is also looking at other types of lenses. "Right now, we're co-sponsoring a study with CooperVision and Humphrey that uses topographic data to fit soft toric lenses," she said. "This won't necessarily change our software, but it will focus on how to use the software to fit the lens."

Ms. Brandau said today's topography systems and software can help optometrists differentiate their practices in a competitive contact lens market. "There are so many ways for patients to get their lenses, not just from their clinicians," she said. "The more difficult-to-fit patients would benefit from this type of software, so it might help keep an RGP patient, for example, in your practice."

Ms. Brandau also believes that more ODs will become comfortable with the technology, similar to the way ophthalmologists did when topography was first introduced. "Topography has already been used in ophthalmology for almost 5 years," she said, "and I think it is moving over into optometry. We are seeing that same pattern of acquiring a higher level of comfort with the technology."

For Your Information:

Jean Brandau may be contacted Eye- Sys/Premier, 221 Lathrop Way, Sacramento, CA 05815; (916) 646-2020; fax: (916) 646-0207.

Walter L. Choate Jr., OD, FAAO, may be contacted at 607 Due West Ave., Ste. 111, Madison, TN 37115; (615) 868-4262; fax: (615) 860-2016.

Anne Moskowitz, OD, PhD, may be contacted at 300 Second Ave., Waltham, MA 02154; (800) 358-6639; fax: (781) 290-5885.

Christopher Snyder, OD, may be contacted at University of Alabama at Birmingham, 1617 University Blvd., Birmingham, AL 35294-0010; (205) 934-6768; fax: (205) 934-6758. Neither Dr. Snyder nor Dr. Choate disclosed whether they have a direct financial interest in any products mentioned or if they are paid consultants for any companies mentioned.