Principles of operation, accuracy and precision of an Eye Surface Profiler.
To introduce a newly developed instrument for measuring the topography of the anterior eye, provide principles of its operation and to assess its accuracy and precision.



The Eye Surface Profiler is a new technology based on Fourier transform profilometry for measuring the anterior eye surface encompassing the corneo-scleral area. Details of technical principles of operation are provided for the particular case of sequential double fringe projection. Technical limits of accuracy have been assessed for several key parameters such as the carrier frequency, image quantisation level, sensor size, carrier frequency inaccuracy, and level and type of noise. Further, results from both artificial test surfaces as well as real eyes are used to assess precision and accuracy of the device (here benchmarked against one of popular Placido disk videokeratoscopes).



Technically, the Eye Surface Profiler accuracy can reach levels below 1 μm for a range of considered key parameters. For the unit tested and using calibrated artificial surfaces, the accuracy of measurement (in terms of RMS error) was below 10 μm for a central measurement area of 8 mm diameter and below 40 μm for an extended measurement area of 16 mm. In some cases, the error reached levels of up to 200 μm at the very periphery of the measured surface (up to 20 mm). The SimK estimates of the test surfaces from the Eye Surface Profiler were in close agreement with those from a Placido disk videokeratoscope with differences no greater than ±0.1 D. For real eyes, the benchmarked accuracy was within ±0.5D for both the spherical and cylindrical SimK components.



The Eye Surface Profiler can successfully measure the topography of the entire anterior eye including the cornea, limbus and sclera. It has a great potential to become an optometry clinical tool that could substitute the currently used videokeratoscopes and provide a high quality corneo-scleral topography.
Department of Biomedical Engineering, Wroclaw University of Technology, Wroclaw, Poland.
D Robert
DR
Iskander
Department of Control Systems and Mechatronics, Wroclaw University of Technology, Wroclaw, Poland.
Pawel
P
Wachel
Etosis, The Hague, The Netherlands.
Patrick N D
PN
Simpson
Department of Biomedical Engineering, Wroclaw University of Technology, Wroclaw, Poland.
Alejandra
A
Consejo
Department of Biomedical Engineering, Wroclaw University of Technology, Wroclaw, Poland.
Danilo A
DA
Jesus
D003315:Cornea / Q000033:anatomy & histology*; D019781:Corneal Topography / Q000379:methods / Q000592:standards*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008953:Models, Anatomic; D015203:Reproducibility of Results; D012590:Sclera / Q000033:anatomy & histology*
Fourier profilometry; anterior eye surface; corneal topography; corneo-scleral topography