Dynamic curvature topography for evaluating the anterior corneal surface change with Corvis ST

Abstract

BackgroundThe measurement of dynamic parameters, such as the length of applanation and the amplitude of deformation, is significant for evaluating corneal properties. Most of the corneal properties (related to shape) including the anterior corneal curvature and the thickness of cornea can be easily measured using some existing techniques. However, they only provide the static or pseudo-dynamic analysis. Based on Corvis ST images, the dynamic features after corneal boundaries detection and parameter estimation will be helpful for corneal analysis.MaterialThe study included 40 eyes in normal group (ranging from 19 to 45 years old) and 30 eyes in keratoconus group (ranging from 16 to 40 years old). These eyes were examined by Corvis ST and for each one a sequence of 140 images was obtained. Besides, 11 subjects of each group were also tested by Pentacam.MethodsBy analyzing the video from the Corvis ST imaging, the fully dynamic curvature topography is proposed to evaluate the response of the anterior corneal surface to the air puff. The new method not only quantitatively measures the intact variation of anterior corneal surface but also provides an intuitive way to observe the dynamic change of the anterior corneal surface in the whole air stream process. The proposed method consists of three main steps: cornea segmentation, curvature estimation and integrated visualization. An automatic segmentation method based on the combination of prior knowledge with phase symmetry and asymmetry theory is firstly presented to detect the corneal boundaries. The Landau-new method is then used to estimate the anterior corneal surface. The corneal dynamic topography is finally obtained by combining the dynamic parameters with the original Corvis ST video, which is an improvement of the fusion technique proposed by Li et al.Results and conclusionBy comparing the segmentation results with manual method and built-in method of Corvis ST, the accuracy and robustness of our proposed segmentation method is demonstrated. The correctness of the estimated corneal anterior curvatures is also evaluated by comparing it with that of Pentacam which is considered to be able to provide the first-class measurement currently. The dynamic topography may be used to distinguish the dynamic behavior of normal corneas from that of keratoconus.Electronic supplementary materialThe online version of this article (doi:10.1186/s12938-015-0036-2) contains supplementary material, which is available to authorized users.

In vivo human corneal deformation analysis with a Scheimpflug camera, a critical review

“…Ji et al proposed to apply a segmentation of the distortion images provided by CST and afterwards apply a curvature algorithm. During segmentation, a removal of image impurities and artifact is performed and curvature analysis image by image should provide information useful for corneal disease diagnosis that the authors would publish in a further paper.…”

“…In recent months, some papers have been published or are going to be published about technical enhancements to apply the device to be able to improve the clinical and the scientific usefulness of CST . The common purpose of these papers is to introduce new software or new parameters to increase the quality of corneal analysis performed by this device . Koprowski et al , proposed an algorithm developed from the Corvis image analysis in healthy participants able to evaluate corneal modification during air puff force in a frequency range from 150 Hz to 500 Hz.…”

Eye retraction and rotation during Corvis ST ‘air puff’ intraocular pressure measurement and its quantitative analysis

“…[11][12][13][14][15][16] Moreover, the image sequences allowed authors to propose new models and parameters to describe corneal biomechanics. 12,[17][18][19] In an earlier paper 19 we introduced the parameter Dp/Dx, which describes the characteristic shape of the cornea during maximum deformation and demonstrates a high repeatability among patients (ICC = 0.90) and a relatively low correlation with IOP (r = À0.44). This parameter is likely more related to the corneal biomechanical properties than to IOP values.…”

Depth-Resolved Full-Field Measurement of Corneal Deformation by Optical Coherence Tomography and Digital Volume Correlation

“…Many researchers also use tonometers to study the biomechanical properties of cornea and their relationship to intraocular press (IOP), the fluid pressure inside the eye. Using tonometers IOP can be measured either in a contact way such as Goldmann applanation tonometer (GAT) and Pascal dynamic contour tonometer (PDCT) [17][18][19] or, more recently, in a noncontact way through using an air impulse such as ocular response analyzer (ORA) [20,21] and Corvis tonometer [22][23][24].…”