Contact Lens Case Reports

Composite Corneal Topography

By Patrick J. Caroline, FAAO, & Mark P. André, FAAO

Historically, the capture area of Placido-based videokeratography systems has been limited to a cord diameter of about 8.0mm to 10.0mm. We were first introduced to extending the effective range of a corneal topographer when researchers at the Queensland Institute of Technology introduced “composite corneal topography” (Read et al, 2006). The technique provides limbus-to-limbus corneal topography by collecting five topographical maps: central, superior, inferior, nasal, and temporal. The software then combines data to produce a composite map that extends across the entire corneal surface.

Recently, Medmont incorporated this technology into its E300 corneal topography software.

Data collection begins by first obtaining a traditional central topographical map on a patient's line-of-sight. The patient is then instructed to look five rings up, down, left, and right (Figure 1). The five topographical maps are highlighted (Figures 2 and 3), and immediately the composite map is generated and displayed. Figure 4 shows the traditional capture of the Medmont topographer, measuring a cord 9.6mm, and the new composite map display with a measuring cord of 11.7mm.

Figure 1. Topographical captures are obtained centrally and in the four primary positions of gaze.

Figure 2. The five topographical maps are highlighted for analysis.

Figure 3. Topographical display of the five captured images.

Figure 4. The left image shows the traditional capture display and the right image the expanded, limbus-to-limbus, composite display.

Figure 5 shows the traditional display and the composite display of a patient who has 3.37D of with-the-rule astigmatism, and Figure 6 shows a patient post-refractive corneal surgery. CLS

Figure 5. The traditional and composite display of a patient who has 3.37D of with-the-rule corneal astigmatism.

Figure 6. The traditional and composite display of a patient post-refractive corneal surgery.

For references, please visit www.clspectrum.com/references.asp and click on document #203.