Study of Fundus Pulsation with Fourier Domain Low Coherence Interferometry

Abstract

 

Purpose:

 

Recent studies indicate that the biomechanical properties of the eye may be involved in the development of various ocular diseases. One way to assess these biomechanical properties in vivo could be to measure the ocular tissue movements during cardiac cycle. In this work, we present a novel equipment based on Fourier-domain low coherence interferometry (FD-LCI) and demonstrate its potential to measure in vivo the fundus pulsation at macula and optic disk, in consenting human subjects.

 

Methods:

 

A custom made, fiber based, FD-LCI system is used to obtain the optical path difference (OPD) between a reference surface and the various reflective interfaces of the fundus. The displacement of the fundus is obtained by tracking in real-time the variations in the OPD. The system is characterized by 400 nm accuracy in displacement measurement at 100 Hz sampling rate.

 

Results:

 

Axial movements of macula and optic disk were measured in 23 subjects. A typical example of such recordings along with their corresponding frequency components is shown in the annexed figure. The effective amplitude of macula movement (Mean=27.42 µm SD=±11.01) was found to be significantly lower (P=0.0002, t-test) than the effective amplitude of optic disk movement (Mean=36.19 µm SD±14.81). In addition to the movement at heartbeat frequency, the first harmonic of the movement is clearly visible, and sometimes dominant in some individuals.

 

Conclusions:

 

We have developed an optical system and demonstrated its suitability for measurement of the fundus movements during cardiac cycle. In addition to a difference in the amplitude of the macula and optic disc movement, our preliminary results show that eye is pulsating at twice the frequency of the heartbeat. All together, these results provide new insights into the biomechanical properties of the eye, which can eventually be used to study the pathophysiolgy of different ocular diseases.  

 

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