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 …

Calculating sag height from an ellipse

Sadly, some topography software doesn’t offer the option to calculate sag at a measurement chord, in which case the next best option is to use the ellipse model that, as far as I am aware, is provided by all corneal topography software. This isn’t quite as accurate a determinant for sag corneal height at the peripheral lens bearing point as …

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 …