  Optical coherence tomography (OCT) is a micrometer-scale, volumetric imaging
modality that has become a clinical standard in ophthalmology. OCT instruments
image by raster-scanning a focused light spot across the retina, acquiring
sequential cross-sectional images to generate volumetric data. Patient eye
motion during the acquisition poses unique challenges: Non-rigid, discontinuous
distortions can occur, leading to gaps in data and distorted topographic
measurements. We present a new distortion model and a corresponding
fully-automatic, reference-free optimization strategy for computational motion
correction in orthogonally raster-scanned, retinal OCT volumes. Using a novel,
domain-specific spatiotemporal parametrization of forward-warping
displacements, eye motion can be corrected continuously for the first time.
Parameter estimation with temporal regularization improves robustness and
accuracy over previous spatial approaches. We correct each A-scan individually
in 3D in a single mapping, including repeated acquisitions used in OCT
angiography protocols. Specialized 3D forward image warping reduces median
runtime to < 9 s, fast enough for clinical use. We present a quantitative
evaluation on 18 subjects with ocular pathology and demonstrate accurate
correction during microsaccades. Transverse correction is limited only by
ocular tremor, whereas submicron repeatability is achieved axially (0.51 um
median of medians), representing a dramatic improvement over previous work.
This allows assessing longitudinal changes in focal retinal pathologies as a
marker of disease progression or treatment response, and promises to enable
multiple new capabilities such as supersampled/super-resolution volume
reconstruction and analysis of pathological eye motion occuring in neurological
diseases.
