Selected parameters of the corneal deformation in the Corvis tonometer

Abstract

IntroductionContemporary ophthalmology knows many methods of measuring intraocular pressure, namely the methods of non-contact and impression applanation tonometry. In non-contact applanation tonometers, e.g. the Corvis, the corneal flattening is caused by an air puff. Image registration of the corneal deflection performed by a tonometer enables to determine other interesting biomechanical parameters of the eye, which are not available in the tonometer. The measurement of new selected parameters is presented in this paper.Material and methodImages with an M × N × I resolution of 200 × 576 × 140 pixels were acquired from the Corvis device in the source recording format *.cst. A total of 13'400 2D images of patients examined routinely in the Clinical Department of Ophthalmology, in District Railway Hospital in Katowice, Poland, were analysed in accordance with the Declaration of Helsinki. A new method has been proposed for the analysis of corneal deflection images in the Corvis tonometer with the use of the Canny edge detection method, mathematical morphology methods and context-free operations.ResultsThe resulting image analysis tool allows determination of the response of the cornea and the entire eyeball to an air puff. The paper presents the method that enables the measurement of the amplitude of curvature changes in the frequency range from 150 to 500 Hz and automatic designation of the eyeball movement direction. The analysis of these data resulted in 3 new features of dynamics of the eye reaction to an air puff. Classification of these features enabled to propose 4 classes of deformation. The proposed algorithm allows to obtain reproducible results fully automatically at a time of 5 s per patient using the Core i5 CPU M460 @ 2.5GHz 4GB of RAM.ConclusionsThe paper presents the possibility of using a profiled algorithm of image analysis, proposed by the authors, to measure additional cornea deformation parameters. The new tool enables automatic measurement of the additional new parameters when using the Corvis tonometer. A detailed clinical examination based on this method will be presented in subsequent papers.

Quantitative Analysis of Corneal Energy Dissipation and Corneal and Orbital Deformation in Response to an Air-Pulse in Healthy Eyes

“…Individual frames within the video are analyzed by the inbuilt CST software to produce various unique parameters. are processed using methods previously described extensively by Koprowski et al 14,18 Image analysis includes detection of the anterior corneal edge using the Canny method, morphologic image processing (close operation), and corneal contour. 18 The resulting data are then used to derive pure corneal ðL TR ðn; iÞÞ and orbital ðL TO ðn; iÞÞ components from the total displacement ðL T ðn; iÞÞ (where n indexes pixels in individual columns nÈ(1, N), and i indexes individual frames in the video i È (1,I), respectively).…”

“…14,18 The method has been validated by comparing the results from their algorithms to data from the CST. 14 The correlated data revealed an error of less than 1% in mean SD. From the resulting analysis we obtained the maximum change in pure corneal displacement over the course of the video.…”

“…However, separated components may be derived through external analysis of the CST videos. 14 Application of a cyclic load to viscoelastic materials results in a loss of energy per cycle due to the inherent viscosity in the system. 15 By calculating the area within the loading and unloading curves of the stress-strain graph, the dissipated energy can be determined quantitatively.…”

Scheimpflug camera in the quantitative assessment of reproducibility of high‐speed corneal deformation during intraocular pressure measurement

“…The use of modern methods of image analysis and processing allows for the determination of parameters that were not available in the first versions of the Corvis ST tonometer software (version V1.00r24). By automatic separation of the constant component (the original corneal shape), eyeball reaction and corneal reaction, it is possible to measure, for example, corneal length changes or maximum amplitude of the eyeball deflection . The summary that enables to compare availability of individual parameters is shown in Table .…”

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].…”