Harmonic OCT for real-time retina flattening

Optical coherence tomography (OCT) is a state-of-the art imaging technique which has revolutionized high-resolution medical imaging. Despite its widespread adoption, the inherent trade-off between imaging range and speed of OCT remains a significant challenge. This is particularly true for applications in ophthalmology, where the incessant movement of the eye demands a high imaging speed, whilst the highly-curved surfaces of the retina and cornea require a long detection range. We present a novel method of controlling the imaging depth via opto-electronic phase modulation of the reference arm. Our hybrid approach combines off-the-shelf components and numerical reconstruction. We showcase an eight-fold effective axial range extension at a 400 kHz A-scan rate. Using a fast phase modulation scheme in lieu of a conventional mechanical delay line allowed us to adjust the imaging depth on a per-A-scan basis. This ensures that the surface of interest remains within the axial range, which is limited by the high A-scan rate, even in the presence of significant variations in surface contour. By compensating for the surface shape during acquisition, our approach ensures a high data throughput and avoids the speed-range trade-off. Harmonic OCT can be readily integrated into commercial systems. This can expand the field-of-view of high-speed clinical OCT imaging.