Development of a novel instrument to measure the pulsatile movement of ocular tissues

We demonstrate an optical instrument that can measure the axial displacement of different eye tissues, including the cornea and the fundus. The instrument is based on spectral-domain low-coherence interferometry, which extracts displacement information from sequential axial scans of the eye with 100 Hz sampling frequency and with a precision of 400 nm. Longitudinal retinal and corneal movements were successfully measured in vivo in live rats, and Fourier analysis of the signal revealed the signature of the respiratory and cardiac cycles at 1.0 and 3.5 Hz, respectively. The effective amplitudes of retinal and corneal displacements at the cardiac frequency were found to be about 1.10 and 1.37 mu m, respectively. The synchrony and direction of these two movements relative to the systole and diastole were found to be nearly the same. This novel instrument can be applied to assess biomechanical properties of the eye, which could be important for early diagnosis and for understanding the pathophysiology of glaucoma and other ocular diseases. (C) 2010 Elsevier Ltd. All rights reserved

Measurement of Ocular Fundus Pulsation in Healthy Subjects Using a Novel Fourier-Domain Optical Coherence Tomography

PURPOSE. Anomalies in the pulsatility of the eye have been associated with many types of ocular pathology. Estimation of ocular pulsatility is usually obtained by measuring the variation in the intraocular pressure using tonometry-based instruments. In this work, the authors present and demonstrate the applicability of a novel and noninvasive Fourier-domain optical coherence tomography (FD-OCT) system to measure pulsatile ocular tissue movements. METHODS. The authors simultaneously measured the longitudinal movement of the cornea and the retina driven by the cardiac cycle in 21 healthy volunteers using their custom-made FD-OCT. They calculated the corresponding fundus pulse amplitude (FPA), which is the variation in the distance between the cornea and the retina. RESULTS. It was found that in young, healthy subjects, the cornea and the retina move axially during the cardiac cycle, with almost equal amplitude but with a phase difference ranging between 1 degrees and 20 degrees. The measured FPA was found to be mostly due to the relative phase difference between corneal and retinal movements, and frequency analysis revealed the presence of the harmonics of heartbeat. The root-mean-square values for cornea, retina, and FPA movements were found to be 28 +/- 9 mu m, 29 +/- 9 mu m, and 4 +/- 2 mu m, respectively. The dominant frequency component in corneal and retinal movement was found to be the second harmonic of the heartbeat. CONCLUSIONS. The technique described here is useful for a precise description of FPA and the movement of ocular tissues. Further investigations and technical improvements will be beneficial for understanding the role of choroidal pulsation in the pathophysiology of ocular diseases. (Invest Ophthalmol Vis Sci. 2011;52:8927-8932) DOI:10.1167/iovs.11-785

Pulsatile Movement of the Optic Nerve Head and the Peripapillary Retina in Normal Subjects and in Glaucoma

PURPOSE. To measure the pulsatile movement of neuroretinal tissue at the optic nerve head synchronous with the cardiac cycle. METHODS. We used a noninvasive imaging device based on Fourier domain low-coherence interferometry to measure the pulsatile movements of the optic nerve head, peripapillary retina, and cornea with submicron accuracy along a line across the fundus. We also measured the change in the Axial Distance between the peripapillary Retina and the base of the optic disc Cup (ADRC) during the cardiac cycle. Twelve normal subjects and 20 subjects with open-angle glaucoma were tested. RESULTS. In normal subjects, the mean fundus pulsation amplitude (defined as the fundus movement minus the simultaneous corneal movement) were 13.0 +/- 2.5 mu m, 9.0 +/- 2.1 mu m, and 8.7 +/- 2.9 mu m at the base of the optic nerve head cup, the nasal peripapillary retina, and the temporal peripapillary retina, respectively, compared with 16.7 +/- 6.8 mu m, 17.3 +/- 10.9 mu m, and 12.7 +/- 6.2 mu m for the corresponding values in the glaucoma group (P = 0.26, P = 0.008, and P = 0.12, respectively). The mean changes in ADRC during the cardiac cycle in normal subjects were 10.7 +/- 2.1 mu m and 11.6 +/- 1.8 mu m for the nasal and temporal side of the optic disc, respectively, compared to 14.9 +/- 5.6 mu m and 14.0 +/- 4.9 mu m in glaucoma subjects (P = 0.03 and P = 0.10, respectively). CONCLUSIONS. There was an approximately 11-mu m pulsatile change in the ADRC in normal subjects, and on the nasal side of the disc, this amount was significantly greater in glaucoma patients. (Invest Ophthalmol Vis Sci. 2012;53:7819-7824) DOI:10.1167/iovs.12-983