We use phase-sensitive optical coherence tomography to measure relative motions within the human eye. From a sequence of tomograms, the phase difference between successive tomograms reveals the local axial motion of the tissue at every location within the image. The pulsation of the retina and of the lamina cribrosa amounts to, at most, a few micrometers per second, while the bulk velocity of the eye, even with the head resting in an ophthalmic instrument, is a few orders of magnitude faster. The bulk velocity changes continuously as the tomograms are acquired, whereas localized motions appear at acquisition times determined by the repeated scan of the tomogram. This difference in timing allows the bulk motion to be separated from any localized motions within a temporal bandwidth below the tomogram frame rate. In the human eye, this reveals a map of relative motions with a precision of a few micrometers per second.
We use phase-sensitive optical coherence tomography (OCT) to measure the deformation of the optic nerve head during
the pulse cycle, motivated by the possibility that these deformations might be indicative of the progression of glaucoma.
A spectral-domain OCT system acquired 100k A-scans per second, with measurements from a pulse-oximeter recorded
simultaneously, correlating OCT data to the subject’s pulse. Data acquisition lasted for 2 seconds, to cover at least two
pulse cycles. A frame-rate of 200–400 B-scans per second results in a sufficient degree of correlated speckle between
successive frames that the phase-differences between fames can be extracted. Bulk motion of the entire eye changes the
phase by several full cycles between frames, but this does not severely hinder extracting the smaller phase-changes due
to differential motion within a frame. The central cup moves about 5 μm/s relative to the retinal-pigment-epithelium
edge, with tissue adjacent to blood vessels showing larger motion.