Ms. Malgorzata A. Kowalska Profile

Malgorzata A. Kowalska

at Wroclaw Univ of Technology

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Proceedings Article | 4 September 2009 Paper

Analysis of keratoscopic images for detecting fixational eye movements and ocular surface deformation

M. Kowalska, D. Mas, H. Kasprzak

Proceedings Volume 7447, 74470N (2009) https://doi.org/10.1117/12.825680

KEYWORDS: Eye, Head, Correlation function, Image analysis, Cornea, Motion analysis, Cameras, Blood, Fourier transforms, Cones

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A sequence of videokeratoscopic images was registered using commercially available instrument E300 at a rate of 50 fps. During the 20 seconds measurement, subject's head was fixed strongly. Acquired images were analyzed for detecting fixational eye movements and corneal surface deformation. For this purpose two rings were extracted from each frame and the ellipses were fitted to them, using least square method. The time series of the ellipses geometrical parameters were considered: minor and major axes length as well as the ellipses center and the orientation. The frequency spectra of mentioned parameters were obtained by application of the Fast Fourier Transform. The longitudinal position of the corneal apex was controlled, thanks to the cone side viewer installed inside the videokeratoscope. The average amplitude of the variation of the ellipse's axes length is around 20μm and of the orientation of the ellipse around 0,1 rad. In the signals frequency characteristics, appear the peak corresponding to the heart rate. No clear relationship was found between the variations of the fitted ellipse parameters and the longitudinal position of the corneal apex. The fixational eye movements were examined using two different methods. One of them consists of calculating the correlation function between the first and successive frame of the sequence and searching its maximum. The other is based on tracking the center of the ellipse fitted to particular ring of the videokeratoscopic image. The accuracy of the second method found to be higher. Simple methods proposed in this work can extend the application of videokeratoscopic measurements.

Proceedings Article | 20 November 2008 Paper

Phase dependencies between longitudinal corneal apex displacement of human eye and cardiovascular system

M. Danielewska, M. Kowalska, H. Kasprzak

Proceedings Volume 7141, 714117 (2008) https://doi.org/10.1117/12.822388

KEYWORDS: Electrocardiography, Eye, Correlation function, Blood, Cardiovascular system, Hemodynamics, Lead, Blood circulation, Signal analyzers, Heart

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Intraocular pressure (IOP) varies quasi-periodically due to blood pulsation in vessels inside the eye globe. This variations cause the eye deformations and displacements of the outer surface of the eye. The aim of this paper is to calculate the correlation between longitudinal corneal apex displacement and cardiovascular activity. Using ultrasound transducer at sampling frequency of 100Hz we have measured longitudinal corneal apex displacement (LCAD) of the left eye for 5 subjects. Synchronically we have registered ECG and blood pulsation signals at the same sampling frequency. Cross-correlation function was applied to investigate dependencies between these signals. To find time shift between LCAD and ECG or pulse, the time window of 3 seconds length have been chosen from all signals and had been shifting with the step of 0.01 seconds from 0 to 7s. For each shift the cross-correlation function and its extrema were calculated in the window area. We have obtained information about extrema position of cross-correlation function and its stability in time for particular subjects. The time shift between LCAD and ECG or pulse is individual feature of each subject. Such calculations may lead us to better understanding of pulse propagation in human eye and creation a non invasive method of eye hemodynamics and ocular diagnosis.

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