In vivo volumetric imaging of human limbal and scleral vasculature with 1μm swept source phase-variance optical coherence tomography (SSpvOCT)

Abstract

 

Purpose

 

To acquire in vivo depth-resolved vasculature maps of anterior segment of the human eye [human corneo-scleral junction and sclera] with a 1060nm SSpvOCT system.

 

Methods

 

The peripheral part of the sclera and episclera was imaged in vivo in eyes of healthy volunteers using a SSpvOCT system. This system used a swept-source laser operating at 1060 nm with a sweep repetition rate of 100 kHz (Axsun). This system provided axial resolution of 6 μm in tissue. Multiple B-scans at the same position, referred to as a BM-scan, were used to acquire phase-change measurements required for the phase-variance calculations (software developed at Caltech Biological Imaging Center). Scanning areas of the sclera were 3x3 mm² and 1.5x1.5 mm². The cross-correlation function based motion correction between consecutive intensity images in an axial direction was applied. Average intensity images and phase differences were calculated from sets of B-scans acquired at the same location, and then phase variance data were calculated. Bulk motion removal and histogram-based threshold processing were implemented to remove phase shifts caused by eye motion. The en face depth resolved projection view of the data produced two-dimensional vascular perfusion maps. One subject with scleral melting was also imaged.

 

Results

 

Distinguishable scleral layers containing different vasculature networks were visible. Fig 1 shows SSpvOCT images of the In vivo human sclera: (a) intensity image of a single B-scan, (b) phase image, (c) average intensity image of three B-scans and (d) phase-variance processed image using phase data from the same three B-scans phase data. The total intensity and phase variance projection is also shown (e). Vertical stripes across the image come from the vascular system present in the sclera (blood vessel shadowing effect). The scanning size in the lateral direction is 3 mm and BM-scan spacing is 6 μm. Empty spaces with no signal come from a non-scattering medium such as lymph or aqueous.

 

Conclusions

 

We presented In vivo noninvasive, volumetric imaging of corneoscleral limbus and sclera using a SSpvOCT system. This enables qualitative presentation of vascular networks in the anterior segment of the eye. It promises to provide valuable information about changes in health and disease as well as during and after corneal surgery.

 

 

Figure 1

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)