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

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.

[1]  B W Peterson,et al.  Mechanisms controlling human head stabilization. II. Head-neck characteristics during random rotations in the vertical plane. , 1995, Journal of neurophysiology.

[2]  D. Guitton,et al.  Gaze control in humans: eye-head coordination during orienting movements to targets within and beyond the oculomotor range. , 1987, Journal of neurophysiology.

[3]  D. B. Preston.  Spectral Analysis and Time Series , 1983 .

[4]  N Maeda,et al.  Comparison of methods for detecting keratoconus using videokeratography. , 1996, Archives of ophthalmology.

[5]  H. Barlow.  Eye movements during fixation , 1952, The Journal of physiology.

[6]  RENZO MATTIOLI,et al.  Corneal Geometry Reconstruction with the Keratron Videokeratographer , 1997, Optometry and vision science : official publication of the American Academy of Optometry.

[7]  R. Sergott,et al.  Amplitude of the Ocular Pneumoplethysmography Waveform Is Correlated With Cardiac Output , 1993, Stroke.

[8]  D. R. Iskander,et al.  Evaluating tear film stability in the human eye with high-speed videokeratoscopy , 2005, IEEE Transactions on Biomedical Engineering.

[9]  D. R. Iskander,et al.  The Stability of Corneal Topography in the Post-Blink Interval , 2001, Cornea.

[10]  Sarah L. Hosking,et al.  Spectral content of the intraocular pressure pulse wave: glaucoma patients versus normal subjects , 2002, Graefe's Archive for Clinical and Experimental Ophthalmology.

[11]  D. Hubel,et al.  The role of fixational eye movements in visual perception , 2004, Nature Reviews Neuroscience.

[12]  A. Opstal,et al.  Human eye-head coordination in two dimensions under different sensorimotor conditions , 1997, Experimental Brain Research.

[13]  C. Bolger,et al.  Dominant frequency content of ocular microtremor from normal subjects , 1999, Vision Research.

[14]  D. R. Iskander,et al.  Ultrasonic measurement of binocular longitudinal corneal apex movements and their correlation to cardiopulmonary system [Article in English] , 2008 .

[15]  H. Kasprzak,et al.  Dynamics in longitudinal eye movements and corneal shape , 2006, Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians.

[16]  D. R. Iskander,et al.  Ocular Microfluctuations and Videokeratoscopy , 2002, Cornea.

[17]  S. Klein,et al.  A Corneal Topography Algorithm that Produces Continuous Curvature , 1992, Optometry and vision science : official publication of the American Academy of Optometry.

[18]  A. Soumelidis,et al.  Dynamics of ocular surface topography in healthy subjects , 2006, Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians.

[19]  R. Krueger,et al.  A standardized classification of corneal topography after laser refractive surgery. , 1997, Journal of refractive surgery.

[20]  H. Leibowitz,et al.  A behavioral link between the oculomotor and cardiovascular systems , 1995, Integrative physiological and behavioral science : the official journal of the Pavlovian Society.

[21]  D. R. Iskander,et al.  Ultrasonic Measurement of Fine Head Movements in a Standard Ophthalmic Headrest , 2010, IEEE Transactions on Instrumentation and Measurement.

[22]  D. R. Iskander,et al.  Applications of high‐speed videokeratoscopy , 2005, Clinical & experimental optometry.

[23]  D. R. Iskander,et al.  Dynamics of ocular surface topography , 2007, Eye.

[24]  L. Szczotka.  Clinical Evaluation of a Topographically Based Contact Lens Fitting Software , 1997, Optometry and vision science : official publication of the American Academy of Optometry.

[25]  M. Langham,et al.  A clinical procedure for the measurements of the ocular pulse-pressure relationship and the ophthalmic arterial pressure. , 1978, Experimental eye research.