Laboratory Study
Eye (2007) 21, 1212–1219; doi:10.1038/sj.eye.6702578; published online 25 August 2006
Spectral characteristics of longitudinal corneal apex velocities and their relation to the cardiopulmonary system
H T Kasprzak1,2 and D R Iskander1
- 1Faculty of Health, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia
- 2Faculty of Basic Problems of Technology, Institute of Physics, Technical University of Hrocean, Wroclaw, Poland
Correspondence: DR Iskander, School of Optometry, Queensland University of Technology, Victoria Park Road, Kelvin Grove, Brisbane, Queensland 4059, Australia. Tel: +61 738645644; Fax: +61 738645604; E-mail: d.iskander@qut.edu.au
Received 25 February 2006; Accepted 28 July 2006; Published online 25 August 2006.
Abstract
Purpose
To study the naturally occurring kinetic characteristics of corneal surface.
Methods
The right eyes of three subjects (young, early presbyope, and presbyope) were examined. Cardiac signal and longitudinal corneal apex movements were simultaneously measured with electrocardiography (ECG) and a high-speed videokeratoscope, respectively. Time, frequency, and combined time–frequency representations of the acquired signals were derived to establish their temporal and spectral contents. Coherence analysis was used to assess the correlation between the corneal apex velocities and the cardiopulmonary system.
Results
In all measurements, longitudinal corneal apex velocity signals showed close correlation with the corresponding ECG signals. The signatures of the pulse frequency, which was inferred from the ECG spectra and their variations in time, were clearly visible in the spectral content of corneal apex velocities. For the young subject, the correlation was the strongest and all of the spectral content of the pulse signal including the harmonics was propagating to the corneal apex velocities. For the other two subjects, there was a clear propagation of the pulse signal itself but not of all pulse harmonics.
Conclusions
Longitudinal movements of the corneal apex are closely related to the cardiopulmonary system. The differences in propagation of pulse harmonics to the corneal apex velocities for different subjects suggest that the frequency characteristics of apex velocity could be related to pulsative variations in the intraocular pressure and biomechanical properties of the eye. These findings could potentially be used in noninvasive assessment of the hemodynamic status of the eye with high-speed videokeratoscopy.
Keywords:
longitudinal eye movements, high-speed videokeratoscopy, intraocular pressure, noninvasive assessment of the ocular pulse
