Do you still think a corneal topographer only belongs in surgical centers? Here are ways to extend its applications in optometric practice.

by Jeffrey S. Eisenberg, Senior Editor

You've probably faced the kind of clinical puzzle optometrist Loretta Szczotka encountered when an 18-year-old keratoconus suspect came to her clinic at Cleveland's Case Western Reserve University. Best-corrected spectacle acuity was 20/50 O.U. Slit lamp evaluation revealed a Fleisher's ring in each eye. Yet, there was no scarring or Vogt's striae in either eye. Did he in fact have keratoconus? Corneal topography revealed inferior steepening—a classic sign of keratoconus. That nailed the diagnosis.

The puzzle wasn't complete, however, Dr. Szczotka corrected his vision to 20/20 with RGPs, but every lens she tried decentered nasally. Dr. Szczotka again turned to topography for clues. The tangential map revealed well-centered cones, so she concluded that her patient's extremely taut lids forced the lenses to settle nasally. She hopes a piggyback soft lens will improve centration.

This case isn't unique. A few years ago corneal topography may have seemed futuristic, but today it has increasing applications. Software advances are pushing that utility. "[Topography] is letting doctors see more of the cornea than they ever could before, and the quality and sophistication of these instruments has become good enough that you can measure repeatedly each time," says Michael D. Twa, O.D., of the University of California, San Diego.

Here's how those advances can benefit your practice.

Keratoconus Detection
Today's software allows you to identify keratoconus suspects and subtle cases of keratoconus earlier than previous versions. This is especially important as more patients consider refractive surgery, which is contraindicated in keratoconus patients.

Manufacturers have developed numerical indices that give you the probability that an eye may be keratoconic. For example, Zeiss Humphrey Systems' Pathfinder software for its Atlas topographer relies on three indices: the cornea's asphericity; corneal irregularity; and mean toric keratometry. The latter compares elevation data from a best-fit toric reference surface to the actual cornea. Based on these indices, Pathfinder distinguishes between a normal cornea, corneal distortion (pseudokeratoconus), subclinical keratoconus and keratoconus. The software also allows you to monitor changes over time.

Dicon's CT-200 topographer features an automated bull's-eye target that looks for unusual corneal elevations. If there's significant elevation, it displays a tangential map, shows a bull's-eye in the suspect area, provides an index level and describes the significance of the peak index. The CT-200 can store and print several custom printouts to create a keratoconus report.

Meanwhile, Tomey Corporation revised its keratoconus screening program for the TMS-3 AutoTopographer. The program includes two analysis methods: the new Smolek/Klyce method, which distinguishes keratoconus suspect patterns from astigmatism, pellucid marginal degeneration, contact lens warpage and others, and can trace changes over time; and the Klyce/ Maeda method, which analyzes several indices to calculate clinical keratoconus-like patterns.

Euclid Systems plans to introduce a new topographer in the coming months that will measure 16mm across the apex, convert height maps into curvature, perform eccentricity analysis and provide K values. It also will allow you to e-mail maps to a nationwide panel of keratoconus specialists.

Even with improved keratoconus detection software, optometrist Edward S. Bennett, of University of Missouri-St. Louis School of Optometry, offers a precaution: "You can't diagnose keratoconus with a topography system, because keratoconus depends on slit lamp findings that are pathognomonic for the disease. But it may tell you, 'I think we have keratoconus.'"

Comanaging Refractive Surgery
Of course, corneal topography is the standard of care for screening refractive surgery candidates. Besides ruling out keratoconus, programs such as Dicon's refractive module for the CT-200 print maps you can use to assess if the patient is suitable for refractive surgery. It also shows the elevation of the cornea in microns.

Bausch & Lomb Surgical's Orbscan system, meanwhile, gets high marks from Lake Oswego, Ore., ophthalmic technician Patrick Caroline. He uses it to map the anterior and posterior surfaces of the cornea, and to determine anterior chamber depth and corneal thickness. "The significance is for better determining the depths of ablations for LASIK, whether or not an individual would be a candidate for LASIK based on [his or her] their corneal thickness," he says

Software advances also can mean improved post-op care for your patients, especially those who present with compromised acuity. "You get another diagnostic tool to determine why that is," says Jon K. Hayashida, O.D., of Cerritos, Calif.

Dicon's refractive module can display the patient's pre-op, post-op and most current exams. A K-trend graph shows the major and minor keratometer powers over time. The surgeon can view any irregularities, compare maps, and decide whether the patient would benefit from re-treatment.

Zeiss Humphrey's Atlas includes what's called a Healing Trend/Stars display, a series of five maps with information on the healing changes following surgery. The display uses serial topography to show a trend in the curvature or power of the cornea postoperatively or following contact lens wear. It can detect surface changes and how they affect vision, and help you decide whether to change medications.

Another topography unit, the Keratograph from Oculus, offers a statistical program for collecting pre- and post-op data and treatment parameters of patients. The program then compiles links, statistics and graphic images for quality control.

Contact Lens Fitting
Although there have been no major advances in contact lens fitting software, manufacturers continue to add information to their databases. Some include every lens available. The programs provide a simulated fluorescein pattern and can link the topographer to the contact lens lab.

These programs use corneal technology information to design the lens rather than just take a few spots on the cornea, and use simulated K values, says Dr. Bennett. He estimates that nine times out of 10, the actual fit is similar to the simulated one.

Rather than going through lengthy trial fitting of lenses and doing fluorescein patterns, you can create the fluorescein pattern on the topographer and really reduce chair time," adds Dr. Hayashida, who is CooperVision's vice president for clinical affairs.

Dicon has added more contact lenses to its contact lens module. The software helps organize your favorite lenses, shows you the best fit for what's available for that particular lens type, and provides a simulated fluorescein pattern. The software also will rule out a spherical lens if the patient has significant astigmatism.

Oculus combines a built-in keratometer with corneal topography in its Keratograph. It measures 22,000 points with 22 rings. Output modalities include 3-D presentation, overview image, fluorescein simulation and Fourier analysis. The database contains more than 20,000 contact lens geometries. One option allows you to check the posterior surface topography of RGP lenses.

Topcon also combines topography with an auto-refractor and auto-keratometer in its KR-8000PA unit. Optional software provides full comparison data. The system lets you design custom contact lenses; it, too, helps detect keratoconus.

Corneal topography may also help in fitting soft toric contact lenses. Last month, Dr. Szczotka reported a retrospective study in which she achieved a 65% success rate fitting CooperVision's soft torics using the company's fitting guidelines. She anticipates a 90% success rate by modifying the fitting guide according to baseline topographic findings and new indices she and her colleagues can generate from topography files.

Monitoring Corneal Changes
Virginia Beach, Va., optometrist Kenneth Lebow says he uses topography routinely in his practice to monitor changes induced by contact lens wear over time.

One example: corneal distortion secondary to hydrogel lenses. "Many of us assume that soft lenses—even thin, draping soft lenses—have no effect on the cornea when we know that certain corneas are more susceptible to changes than others," Dr. Hayashida says. Topography readings can indicate when you may need to switch designs or materials.

Orthokeratology
Though reverse geometry lenses may be effective, the outcome can be difficult to predict without detailed information of the corneal surface, its asphericity and how much it flattens in the periphery.

This is another area where topography software now allows more predictability. The Keratron topographer from EyeQuip determines how much corneal tissue must be displaced and what shape the lens should be to achieve the desired Rx. "It's marrying several areas of technology: corneal imaging, contact lens manufacturing and contact lens design principles," Dr. Twa says.

Euclid is conducting an FDA orthokeratology study. Preliminary data show a 90% success rate for ortho-K designs from combining topography and K-readings. Like its keratoconus network, the company also has a team of ortho-K specialists for consultation.

Topcon's 8000PA allows you to modify the contact lens design and simulate the fluorescein pattern so you get the best fit to adjust the corneal shape. This helps you decide which contact lens you'll use for that patient.