Dynamic point shifting with null screens using three LCDs as targets for corneal topography

In this paper, the use of three liquid crystal displays (LCDs) as targets for an experimental corneal topographer is proposed. The main advantage is that the geometrical pattern in the target can be modified without moving any mechanical part to apply the dynamic point shifting (DyPoS) method. Some results on the capabilities of the LCDs, obtained with photo frames, for measuring a 6.37 mm radius of curvature calibration sphere, and applying the DyPoS method, are presented. It is shown that the error in measuring the radius of curvature with DyPoS is reduced to 3% of the real value and the RMS in elevation or sagitta differences is around 15 μm, 30% or 66% of the values obtained without DyPoS, respectively.