Importance of good tear film when measuring corneal topography

Most corneal topographers in clinical practice use Placido disk image capture technology and typically come in two different versions: either bowl type like the Oculus Keratograph; or cone type like the Medmont E300. There are other approaches to measuring topography, like slit scanning (B&L Orbscan) and Scheimpflug (Oculus Pentacam) systems, each with their own differences in methodology but essentially, they …

Eight steps to better corneal topography

Corneal topography is your main diagnostic tool for Orthok lens fitting. Get this right and everything else becomes so much easier. Do it badly, especially at first fit, and the rest of the journey will become harder. Fortunately, it’s not that hard a skill to learn and once you have the hang of it you will easily be able to …

Modelling corneal shape

Each corneal topography image holds a vast array of data measurement points that need to be broken down into a more user-friendly form. By example, the Medmont E300 captures data at around 6,000 locations and displays each location in four different formats. I think it’s fair to say that any lens design requiring manual entry for each of these locations …

Descriptors of elliptical shape

The different terminology used to define ellipse shape can seem confusing at first. ‘Eccentricity’ is the preferred mathematical term, but the terms ‘Shape Factor’ and ‘Asphericity’ are also in widespread use. So which should you use? When it comes down to it this will usually depend on what is specified by the design you are using so from your topography …

Improving accuracy of first fit selection

This is where we turn to the multiple topography maps that in an earlier post I suggested you capture, because through averaging we can obtain a more reliable measure and remove potentially poorly captured maps. Hopefully your corneal topography software will do this for you, otherwise, it is not too hard to work out by adding up the individual K values …