Imaging the relationship of the capillary plexuses to plexiform layers with visible light Optical Coherence Tomography

Abstract

Purpose : We employ visible light Optical Coherence Tomography (OCT) to investigate the anatomical relationship between the intermediate capillary plexus (ICP) and the inner plexiform layer (IPL) substrata.

Methods : An upgraded spectral/Fourier domain visible light OCT prototype, with 1.0 micron axial resolution, imaged human subjects (n = 2; 2 males; 33.5 ± 9.2 years) without history of ocular pathology. A series of 30 frames at 15 y-locations (2 repeats) was acquired with a 4.5 mm fast axis range and a 0.18 mm slow axis range at 20–40 kHz imaging speed. OCT intensity images, labelled as “OCT,” were generated by motion correction and intensity averaging along the slow (y) axis. For angiograms, labelled as “OCTA,” complex subtraction was performed following correction of axial and lateral image shifts as well as phase shifts. A normalization image was formed by complex summation of the two repeated images, followed by motion correction and intensity averaging across y-locations, and finally spatial blurring to reduce speckle. The maximum intensity projection along the slow (y) axis of the magnitude-squared of the complex difference was normalized to the normalization image prior to display. OCT and OCTA longitudinal reflectivity profiles were compared.

Results : Depth profiles demonstrated the OCT IPL pentalaminar pattern, the outer plexiform layer (OPL), as well as OCTA peaks for the ICP and deep capillary plexus (DCP) (Figure 1A-C). Shifts were calculated between the outermost peak of the IPL and the ICP distribution peak (IPL-ICP), as well as between the peaks of the OPL and DCP distributions (OPL-DCP) (Figure 1D-E). A shift in the inner direction was considered to be positive. Shifts (mean ± std. dev.) are shown for IPL-ICP and OPL-DCP (Figure 1F).

Conclusions : Our results show that the ICP microvasculature is situated just outer to the off-sublamina of the IPL. We conclude that the vasculature do not align precisely with the pentalaminar IPL reflectivity pattern on OCT.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Figure 1. A-B) Overlay of OCT angiography (OCTA, green) on OCT (red) shows the relationship between capillary plexuses (green) and plexiform layers (red) in cross-section (B) and after flattening, in depth profiles (C). D-F) Shifts between depth profile peaks, defined as shown in E, reveal that the outermost (S1) IPL peak is inner to ICP, while OPL is outer to DCP.