Fig. 1. Schematic of the circular interleaving scan method for OCTA imaging. (a) Circular scan trajectory. The scan area is divided into the slingshot (1X), double-shot (2X), and triple-shot (3X) interleaved OCTA imaging zones, each containing 90 circles. ΔL: spatial sampling interval in the circumferential direction; ΔR: spatial sampling interval in the radial direction. (b) The X and Y scanner waveforms and the corresponding data acquisition signals from the line scan camera. (c)–(e) B-scan time and angular and linear scan velocities as functions of the scan circle number (k=1: 270). The blue dashed lines indicate the reference time/velocity without interleaving, and the orange solid lines indicate the time/velocity with the interleaving scan protocol.

Fig. 2. Coordinate-transformation-based image processing for iris vascular imaging in circular interleaving scan OCTA. (a) Extraction of B-frame blood signals using a 2X interleaving example. (b) and (c) Projection of blood flow signals in Cartesian (triangular map) and polar (circular map) coordinates, respectively. Note that the discontinuity in blood signals is due to eye movements. (d) An interpolation process that transforms the triangular map into a rectangular map, making vascular signals predominantly vertically parallel and motion-induced bright lines horizontally parallel. (e) Rectangular blood flow map after the removal of bright lines, realignment of vessels, and enhancement of contrast. (f) and (g) Triangular and circular diagrams representing iris vascular imaging after image processing. The inset in panel (g) demonstrates improved connectivity and image quality compared with those in panel (c).

Fig. 3. Comparison of circular and raster scans in iris OCTA imaging, showing enhanced vascular imaging contrast and improved quantification accuracy in circular scan OCTA by eliminating angular-dependent blind spots. Seven repetitive measurements were performed for each protocol (scan parameters detailed in Table 1) on subject 1’s left eye, which was constricted for better visualization. For quantification, eight zones were defined based on the regions (pupillary and ciliary zones) and directions (S, superior; I, inferior; T, temple; and N, nasal). (a) Large-FOV circular interleaving scan. (b) and (c) Horizontal and vertical raster scans. Red dashed lines delineate angular-dependent blind spots. (d) and (e) Quantification of vessel density and vessel numbers (mean ± SD) for pupillary zones (1–4) and ciliary zones (5–8). The stars indicate zones with blind spots.

Fig. 4. Angular analysis of iris vasculature using coordinate transformation for the circular interleaving OCTA imaging with large-FOV and high-density scan protocol. Scan parameters are detailed in Table 1. Subject 1’s right eye was constricted for better visualization, with seven repetitive measurements performed for each protocol. S, Superior; I, Inferior; T, Temporal; and N, Nasal. (a) and (b) Examples of OCTA imaging and corresponding marked vasculature networks in circular and rectangular coordinates, with repetitive visualization results. (c)–(f) Quantification of vessel density and vessel numbers within each 30 deg angular range.

Fig. 5. Comparison of the iris structure imaging between raster and circular scan methods. (a) Volume image and (b) en face and cross-sectional images of the iris tissue structure using a raster scan. Scan field: 64mm2 (450×450 A-lines); data acquisition time: 3.25 s (duty cycle: 82.00%); spatial sampling interval: 17.8μm. (c) Volume image and (d) en face and cross-sectional images of the iris tissue structure using a circular scan. Scan field: 70.8mm2 (270 circles, the k’th circle had 6k A-lines; there were a total of 36,585 A-lines); data acquisition time: 2.89 s (duty cycle: 99.88%); spatial sampling interval: 17.6μm in the radial direction and 18.4μm in the circumferential direction. The red and green arrows in the cross-sectional images showcase the superficial and embedded crypts.

Fig. 6. Home-built spectral domain optical coherence tomography (SD-OCT) system for human iris structure and vasculature imaging.¹⁴ (a) Schematic of the SD-OCT system, comprising a superluminescent diode) light source, sample and reference arms, and a spectrometer. The iris scan objective is specifically designed for human iris imaging. The spectrometer employs a grating and a prism to disperse light in the wavenumber (k) space. (b) and (c) Sensitivity fall-off and full width at half-maximum of the point spread functions in the depth direction. (d) The iris scan objective focuses light onto the iris plane. (e) RMS values of the focused spot radius in the lateral direction. (f) and (g) Calibration of lateral and axial distortions (mean ± standard deviation). (h) Corner-to-corner cross-sectional image of the human iris, averaged from 10 measurements.

Fig. 7. Comparison of different scanning patterns and driving waveforms for galvanometer scanners and their corresponding data acquisition signals for OCT structural imaging. (a) and (b) Raster scan. (c) and (d) Spiral scan. (e) and (f) Circular scan. The scanning patterns are shown in the top row, the driving waveforms are shown in the middle row, and the data acquisition signals are shown in the bottom row.

Fig. 8. Distortion correction in circular-scan OCT via control signal phase compensation. (a) Uncompensated image. (b) Corrected image using active phase compensation [Eq. (3)].