Measurement of the Pulsatile Movement of Ocular Tissues With Fourier-Domain Low-Coherence Interferometry

Abstract

Purpose: : There is increasing evidence that the biomechanical properties of the eye may be involved in the development of various ocular diseases. However, there currently exists no technique with both sufficient time and spatial resolution to measure these biomechanical properties in vivo. In this work, we demonstrate an optical instrument capable of measuring in vivo the movement of different ocular tissues due to cardiac pulsations, which is an indicator of the biomechanical properties of the eye. We demonstrate the performance of the instrument on a anesthetised rat by measuring the movement of the cornea and the retina.

Methods: : The developed instrument is based on Fourier-domain low-coherence interferometry (FD-LCI). A broadband light source is used to illuminate both the eye and a fixed reference surface. After recombining the reflected beams in a fiber coupler, a diffraction grating spatially separates the different wavelength components that form an interference pattern on a photodetector array. Fourier analysis of the spectral interference signal provides information on the relative position of the reflective interfaces in the sample relative to the reference surface. By tracking in real-time the variations in the interference signal and by using digital signal processing, the displacement of the eye tissue interfaces can be measured.

Results: : The performance of the device is characterized by a precision (that is, the reproducibility of the measurement) of 400 nm in displacement measurements at 100 Hz sampling rate. Using this system, we measured the displacement of the cornea and the retina resulting from cardiac pulsations. For both tissues, the peak-to-peak amplitude of the movement was estimated over 30 cycles. The average peak-to-peak values with standard deviation are (4.0 ± 1.0) µm and (4.6 ± 0.7) µm for the retina and cornea, respectively. It was also found that the cornea and the retina move along the same direction during systole and diastole.

Conclusions: : We have developed an optical instrument and demonstrated its suitability for measuring the ocular tissue movement during cardiac cycle, which would provide insights into the biomechanical properties of the eye. These promising results show that this instrument could eventually be used for the study of the pathophysiolgy of different ocular diseases.

Keywords: eye movements • eye movements: recording techniques • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)