Spotlight ON TECHNOLOGY & TECHNIQUE

A Tool That Provides Improved Corneal Topography Screening of Refractive Patients

By Leslie Goldberg, Associate Editor

"Our practice was looking for the best corneal mapping system available and found it in the Magellan Mapper [MM1, Nidek, Fremont, Calif.]," says Byron Stratas, M.D., in private practice at Eye Associates of Wilmington, P.A. in Wilmington, N.C. Dr. Stratas says that after considering information found in a published report on corneas at risk,¹ he felt the need to obtain an accurate topography system to complement other tests he performed for corneal biomechanical stability.

Selecting the Magellan Mapper

Dr. Stratas was searching for an improved biomechanical screening of potential refractive patients. "We wanted to make sure we were not operating on people we shouldn't be, but not excluding people that we shouldn't," says Dr. Stratas. "Additionally, we needed a good way to determine the true refractive power of the front of the cornea."

In looking for better biomechanical screening, Dr. Stratas found two valid, but distinct schools of thought — tomography, which provides full-thickness anterior and posterior elevation analysis and the Klyce-Smolek type of analysis of anterior curvature patterns — topography.

"We obtained the most accurate tomographer, the Pentacam (Oculus, Inc., Dutenhofen, Germany). However, tomographers do not appear to be the best at evaluating the anterior curvature and refractive patterns of an eye." So, Dr. Stratas had a better tomographer, but was still looking for a system that best evaluated anterior curvature patterns. This led him to the Magellan. "Today, we use both screening methods for validation. They run on the same computer — this is super technician- and patient-friendly," says Dr. Stratas.

Features and Benefits

"The MM1 has all of the features that we wanted," says Dr. Stratas. "It is extremely accurate, measuring 21,600 data points. In addition, instead of extrapolating the data points for the central 3 mm of the cornea, the MM1 measures 5,760 points in that central 3 mm."

The MM1 also has the highest resolution of any placido topographer, with 60 rings and the industry's best distribution of 21,600 measured data points. It accurately tracks without "ring lock" so highly irregular corneas provide meaningful data, says Nidek.

■ Corneal Navigator. The Mapper uses the Corneal Navigator developed by Stephen Klyce, Ph.D., and Michael Smolek, Ph.D., to screen for eight different corneal conditions including pellucid marginal degeneration (PMD) and keratoconus. Utilizing corneal statistics developed by Dr. Klyce, this neural network software offers capabilities far beyond simple keratoconus screening, which may lead to false positives postoperatively and false negatives for pellucid.

The MM1 automatically determines corneal features and shows, by percentage, the probable state of the cornea.

"The corneal navigator module neural network provides an extra tool to screen for corneal conditions that can be tricky to see with lower resolution systems, such as pellucid marginal degeneration," says Dr. Stratas.

■ Highest industry resolution and increased accuracy. The placido-based, low-light level cone works in conjunction with a dual-border detection algorithm leading to the highest resolution in the topographic field. The high resolution, in addition to the offset indexes, increases the reliability of the exams, says Nidek.

"The K readings from the MM1 provide quality control for preoperative keratometry as an adjunct for IOL power calculations. It is accurate and something I find very useful," says Dr. Stratas. "It measures the average central corneal power in the 3 mm zone. Corneal aberrometry can be directly measured and is used to help select an IOL to complement the existing corneal spherical aberration." The MM1 also estimates the visual potential of the cornea. This helps in preoperative counseling of patient expectations, says Dr. Stratas.

The cone-based system provides more rings than a disc-based system — while the MM1 projects 30 rings, it gathers 60 rings of data. "The accuracy on the corneal surface is unsurpassed in my opinion," says Dr. Stratas. "The MM1 will give a range of expected best visual potential of the cornea, which helps in preoperative patient counseling."

■ Innovative software. The MM1 clearly labels interpolated and extrapolated data and uses color-coded offset indices to inform the practitioner of exam reliability. The easy-to-use interface helps the operator to easily and quickly access data.

"The printout is helpful because it tells you if alignment is accurate, which is very important in topography," says Dr. Stratas. "It also gives immediate feedback. The printout provides everything I need, including a grading system to assure the alignment is accurate. The software incorporates two decades of software development into one screen."

■ Design. The MM1's ergonomic design, fixation target and laser spot allow easy alignment, reduce examination time and require minimum patient cooperation.

"My technicians find it quick and easy to use, so they are inclined to perform multiple tests to confirm the validity of unusual findings," says Dr. Stratas.

"Because of our diagnostic capabilities, our cataract and refractive volume has increased and we have become a regional referral center for the hard-to-please patient," says Dr. Stratas. "The bottom line is that my technicians find it easy to get what we need for our patients and that is a very important feature." OM

Reference

1. Binder PS, Lindstrom RL, Stulting RD, et al. Keratoconus and corneal ectasia after LASIK. J Refract Surg. 2005;21:749-752.

For more information on Nidek Co., Ltd.'s Magellan Mapper, visit their Web site at www.nidek.com/mm.html.
Dr. Stratas has no financial ties to Nidek.