Ultrahigh-Resolution SD-OCT of the Human Retina with Extended Imaging Range Using Reference Arm Length Modulation

Abstract

Purpose : To develop high-speed, extended-range, ultrahigh-resolution spectral-domain optical coherence tomography (UHR SD-OCT) and demonstrate scan protocols for retinal imaging.

Methods : A high-performance 840-nm spectrometer based on a high-speed 2048-pixel camera with line rates up to 250 kHz was used to achieve 3.1-µm axial resolution and 1.3-mm 6-dB imaging range in tissue. Reference arm length modulation (ReALM) allowed the axial imaging window to follow the contour of the retina, in order to increase the effective imaging range. High-definition (HD) raster scans covering 9 mm×6 mm field of view (FOV) with 1800×241 A-scans were acquired in 3.8 seconds to visualize cross-sectional details of the outer retina. Software-motion-corrected volumes were generated from a pair of perpendicular raster scans, each of which covered 6 mm×6 mm or 9 mm×9 mm FOV with 500×500 A-scans acquired in 2.3 seconds. Linear signal display (no logarithmic compression) was selectively used for enhanced UHR visualization.

Results : UHR SD-OCT was evaluated at 128 kHz and 250 kHz A-scan rates with motion-corrected volumes and HD raster scans in healthy subjects and subjects with dry age-related macular degeneration (AMD). In healthy eyes, the rod interdigitation zones, retinal pigment epithelium (RPE), and Bruch’s membrane were clearly resolved. Eyes with dry AMD exhibited reduced sharpness and impairment of these structures.

Conclusions : The proposed UHR SD-OCT system achieves high-speeds and extended effective imaging ranges, thereby enabling wider FOV and practical volumetric scan protocols. These developments may facilitate clinical UHR studies of outer retinal markers of AMD progression.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Motion-corrected volume generated from a pair of 500×500 raster scans over 9 mm×9 mm macular area of an eye with dry AMD. (A1-A7, B1-B7) ReALM compensates for the retinal contour across different B-scans. (C1-C7) motion correction removes the axial displacement introduced either by patient motion or by ReALM. Scale bars: 1 mm.

 

B-scans at the position 2mm superior to the fovea, taken from 1800×241 HD raster scans covering 9 mm×6 mm macular area. Linear signal display of a 125-um outer retinal slab shows that the photoreceptor layers appear less sharp in dry AMD (A, C) compared to the age-matched controls (B, D). Scale bars: 500 μm.