Abstract
Purpose :
Hyper-parallel optical coherence tomography (HP-OCT) is a high-speed snap-shot spectral domain OCT system robust to patient movement, and particularly well suited for anterior biometry. We demonstrate that HP-OCT can measure cornea and scleral topography over an extended field of view of 20x20 mm and so provides complete OCT topography in a non-invasive approach enabling assessment for scleral lens custom design, fitting and on-going post fit eye health assessment.
Methods :
HP-OCT uses a parallel sampling scheme with a grid of 1008 beams that are generated from an 840nm SLED and a 2D micro-lens array of 0.4mm pitch. A grating based spectrometer then disperses all beams on to a 2D CMOS sensor with a frame rate of 300Hz producing a scan speed of 302,400 A-scans per sec. Standard scan pattern options produce refraction corrected true corneal 3D volumes with fields of view of 16.8x 9.6mm and 16.8x14mm captured in 1s and 2s, respectively. Small scan angles compared to point scanning systems minimize distortion and enable accurate stitching. Here we demonstrate that an extended topography coverage of 20x20 mm can be obtained by stitching off-axis volumes.
Results :
In Figure 1 we show maximum intensity projection en face images of the 5 volumes to be registered. The fixation offsets of the off-axis volumes are 25 degrees. Rigid body volumetric registration is used to align off-axis volumes with the on-axis volume. The combined volume and sample B-Scans are shown in Figure 2. A comparison of registered anterior surfaces shows that, in common regions of good signal quality, the height difference is less than 5 μm.
Conclusions :
The parallel nature of the HP-OCT system enables it to generate true 3D volumes that are free from distortion due to movement and scanning artifacts. This enables accurate scleral measurements over large fields of view to be created from combined off-axis captures. (In future work, we envision a wide field single capture with on-axis fixation and a modified 4s scan pattern and the ability to incorporate OCT Angiography across this same ultra-wide scan.)
This is a 2021 Imaging in the Eye Conference abstract.