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PLoS One. 2015 Nov 23;10(11):e0139541. doi: 10.1371/journal.pone.0139541. eCollection 2015.

Effect of Misalignment between Successive Corneal Videokeratography Maps on the Repeatability of Topography Data.

Bao F1,2, Wang J3, Huang J1,2, Yu Y1,2, Deng M1,2, Li L1,2, Yu A1,2, Wang Q1,2, Davey PG4, Elsheikh A3,5.

Author information

The Affiliated Eye Hospital of WenZhou Medical University, Wenzhou, 325027, China.
The institution of ocular biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province 325027, China.
School of Engineering, University of Liverpool, Liverpool L69 3GH, United Kingdom.
College of Optometry, Western University of Health Sciences, Pomona, CA 91766, United States of America.
NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, United Kingdom.



To improve the reliability of corneal topographic data through the development of a method to estimate the magnitude of misalignment between successive corneal videokeratography (VK) maps and eliminate the effect of misalignment on the repeatability of topography data.


Anterior and posterior topography maps were recorded twice for 124 healthy eyes of 124 participants using a Pentacam, and the repeatability of measurements was assessed by calculating the differences in elevation between each two sets of data. The repeatability of measurements was re-assessed following the determination of the magnitude of misalignment components (translational displacements: x0, y0 and z0, and rotational displacements: α, β and γ) between each two data sets and using them to modify the second data set within each pair based on an Iterative Closest Point (ICP) algorithm. The method simultaneously considered the anterior and posterior maps taken for the same eye since they were assumed to have the same set of misalignment components. A new parameter, named Combined Misalignment parameter (CM), has been developed to combine the effect of all six misalignment components on topography data and so enable study of the association between misalignment and the data repeatability test results.


The repeatability tests resulted in average root mean square (RMS) differences in elevation data of 8.46±2.75 μm before ICP map matching when simultaneously considering anterior and posterior surfaces. With map matching and misalignment correction, the differences decreased to 7.28±2.58 μm (P = 0.00). When applied to only the anterior maps, misalignment correction led to a more pronounced reduction in elevation data differences from 4.58±1.84 μm to 2.97±1.29 μm (P = 0.00). CM was found to be associated with the repeatability error (P = 0.00), with posterior maps being responsible for most of the error due to their relatively lower accuracy compared to anterior maps.


The ICP algorithm can be used to estimate, and effectively correct for, the potential misalignment between successive corneal videokeratography maps.

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