Topography Holds Its Own
Even with the advent of wavefront technology, this key tool remains relevant.
BY JOHN PARKINSON, ASSOCIATE EDITOR

Traditionally, corneal topography has been useful to doctors with its variety of diagnostic capabilities. As you know, it can be used to diagnose astigmatism, identify pathologies, pre-screen refractive surgery patients and follow-up on post-refractive-surgery patients. But some may wonder whether newer technologies, most especially wavefront, have diminished topography's role. With this in mind, Ophthalmology Management asked several doctors to provide their thoughts on this issue and topography's overall role in ophthalmology today.

Then and Now

According to Stephen Klyce, Ph.D., creator of the original color-coded topographic mapping system, topography grew up with refractive surgery. He talks about the motivating factor behind this mutual development.

"The driving force for development of corneal topography back in the early 80s was the development and widespread application of refractive surgical techniques in the U.S.," Dr. Klyce says. He notes that before the advent of topography, doctors were using other methods to understand the corneal manipulation on post-refractive patients; however, these methods left doctors without any methods to "critically evaluate the consequence of refractive surgery on changing corneal shape."

A topography/refractive relationship has continued and Dr. Klyce says you can see it in postoperative eyes. "With modern refractive surgical techniques, the functional optical zone can be so large and the transition zone can be so well-performed," says Dr. Klyce. "They are so good now when you look at these corneal topographies, you can't tell under normal circumstances that they have been operated upon."

However, viewing refractive results is just one aspect of using topography. When considering potential refractive patients, topography is widely viewed as the gold standard. As a teacher, Dr. Klyce instructs his students to use it preoperatively.

Daniel Durrie, M.D., uses topography preoperatively in his Overland Park Kan., practice. "We do a tremendous amount of surgery on the cornea," explains Dr. Durrie. "You really need to understand the shape of the cornea to really understand what's going on with the surgery. I am looking at how to improve people's optics as much as possible, and [topography] is just as important as my slit lamp exam."

The New Technology On The Block

Even with the advent of wavefront in recent years, Dr. Klyce sees a continued relevancy for corneal topography. He believes it will not be surpassed by wavefront or any other new technologies. Dr. Klyce acknowledges the power of wavefront technology, but he says it has limitations.

"Wavefront technology won't surpass corneal topography analysis for two important reasons. One, at least currently, the resolution of the wavefront devices isn't nearly as high as those of corneal topography devices. That may be overcome in the future," explains Dr. Klyce. "The second problem that will never be overcome is that the wavefront devices will never be able to measure outside of the natural pupil of the eye. Even if we dilate the pupil, we still have considerable territory of the cornea that is important to know the shape of."

Everyone who provided feedback for this article sees wavefront and topography as complementary technologies as opposed to competitive forces. Dr. Durrie performs corneal refractive surgery, IOL implants, etc., and, because he likes to obtain as much information as possible to get a more complete picture of the eye, he uses both wavefront and topography. "We do both tests on any new patients, and in most follow-up [surgical] patients," explains Dr. Durrie.

Scott MacRae, M.D., medical director at the University of Rochester Medical Center's Strong Vision Clinic, and professor of Ophthalmology and Visual Science at the same university, also has a comprehensive refractive surgical practice and concurs that utilizing both technologies is better for analysis. "It's better to use these two together than to be looking at them independently," explains Dr. MacRae. "We use [topography] it in conjunction with wavefront; the two together are a very strong combination."

Hybrid Devices

If any definitive proof was needed to further make the case that corneal topography is still a relevant technology, one has to look no further than the marketplace. The ophthalmic industry is continuing to manufacture topographers, and they are doing so with added features like wavefront. "They [manufacturers] are starting to build machines that can give you the ability to measure topography and wavefront or measure topography and the lens," says Dr. Durrie.

Dr. MacRae is able to utilize both wavefront and topography simultaneously through a workstation tied to one central computer. And while he is already utilizing a machine with dual capabilities, he thinks there is going to be more of these types of devices to come because they give doctors a more complete picture of the eye and they can help to identify the location of the patients' refractive errors.

"I think that systems of the future will combine topography with wavefront so you will get a complete picture," Dr. MacRae says. "You can measure the refractive error and you can measure the corneal topography and you can determine the amount of refractive error that is actually coming from the cornea or the human lens. Having both systems work together allows you to determine what the source of the refractive error is."

Dr. Durrie is also utilizing topographers that have dual features to understand better the source of patients' refractive errors. "It completes the story," he says. "The wavefront is the optics all the way to the retina, the topography gives us the cornea portion of it and some of these new instruments will give us the lens portion." In addition to having wavefront and topography, Dr. Durrie mentions that topographic devices are now being developed to measure the lens.

In the Market

As it appears that topographic technology is not fading, but evolving to adapt new features, here are some tips about what doctors should be looking for when in the market for topographers. For those doctors who are buying their first topographer or even those looking to upgrade present equipment, both Drs. Klyce and Durrie agree that doctors should be talking to colleagues about what topography devices they are using in their offices first.

Dr. Klyce also points out doctors should be looking for machines that have contrasting color scales. However, the palette standard suggested by the American National Standards Institute (ANSI) uses a monotonic gradation of colors which smears out the power contours according to Dr. Klyce. This has led some topography manufacturers to produce machines using the ANSI standard, and Dr. Klyce advises against using them.

"There are several topographers available today that use monotonic gradation of blues and greens and reds that smudge out the contrast between contour intervals. By doing that, one loses any indications of the aberrations emanating from the corneal surface," explains Dr. Klyce. (To read more about this issue, see the sidebar on page 52.)

Dr. MacRae sees the ease of use as one of the key elements to buying. "At one point I had three or four topographers in the same room. One thing you learn is you may have all these different topographers, but your staff will always gravitate to the one that is ergonomically simple and easy to understand."

He also points out that when you buy these machines to consider the company's long term service record and where you have to send the machines out for maintenance because once you become dependent on these machines, you cannot afford to have your topographer out for weeks at a time due to shipping issues.

Staying Power

Topography will continue to provide doctors with diagnostic information and offer other contributions to practices. This cornerstone measurement tool has been instrumental in the refractive field, and it has led to a greater progression in getting a better perspective of the cornea. In tandem with newer technology, topography will create a more complete analysis of the eye. In the process, more sophisticated topographic devices will help enable surgeons to achieve even more remarkable outcomes.