Abstract
The purpose of this study was to evaluate density change in the retinal capillary plexus during intra ocular pressure (IOP) elevation in vitrectomized pigs’ eyes using optical coherence tomography angiography (OCTA). Eight eyes of eight micro pigs received vitrectomy and the IOP was controlled from 15 mmHg (baseline) to 105 mmHg in 15 mmHg increments using a vented-gas forced-infusion system, and then decreased back to normal IOP (recovery state). The spectral-domain OCTA device was set to scan an area of 8.8 × 4.4 mm (30° × 15°) above the optic nerve head for each IOP. The relative vessel density (rVAD) compared to baseline was determined for the total retinal blood flow (RBF) which included major retinal artery and venous vessels, radial peripapillary capillaries (RPCs), superficial (SVP), intermediate (IVP), and deep vascular plexus (DVP). The mean rVAD was 0.890 in RBF, 0.826 in RPCs, 0.817 in SVP, 0.819 in IVP, and 0.794 in DVP at 30 mmHg. While the rVAD of RBF and RPCs decreased to 0.504 and 0.541 at 45 mmHg, the SVP, IVP, and DVP decreased to 0.433, 0.359, and 0.345, respectively. When IOP was normalized, the rVAD was recovered in all layers and the VAD of RBF, IVP, and DVP were higher than baseline (P = 0.040, 0.019, and 0.019, respectively). Retinal capillary density deterioration in each layer was found from 30 mmHg using an OCTA system which showed excellent depth-resolved segmentation of retinal capillary layers even at higher IOPs. Reduction in VAD showed full recovery after IOP normalization.
Highlights
Blood flow that supplies oxygen and nutrients is essential for proper retinal function
The retinal blood flow from major arteries runs exclusively into the superficial vascular plexus (SVP), which divides into radial peripapillary capillaries (RPCs) on one side and the intermediate (IVP) and deep vascular plexuses (DVP) on the other side[1]
Experimental models demonstrated intraocular pressure (IOP) fluctuations during vitrectomy, ranging from 0 to 120 mmHg9, and high IOP (80 mmHg) during vitrectomy can lead to damage of retinal ganglion cells in a rabbit m odel[20]
Summary
Blood flow that supplies oxygen and nutrients is essential for proper retinal function. Human retinal capillaries that comprise the superficial vascular complex consist of the superficial vascular plexus (SVP) and retinal peripapillary capillaries (RPCs) in nerve fiber and ganglion cell layers and intermediate (IVP) and deep vascular plexuses (DVP) in the inner plexiform and outer plexiform layers, respectively[5]. These plexuses represent terminal anastomotic capillary networks supplied by vertically oriented interconnecting arterioles and venules of the SVP6. Radial peripapillary capillaries (RPCs) run parallel to the nerve fiber layer (NFL) around the disc and drain to the IVP or DVP3 The similarity of these microstructures makes the pig a good experimental model for hemodynamic analysis of intra-retinal microcirculation in humans. We observed the changes in capillary density in each capillary plexus according to IOP change through OCTA in a pig model, which is a large animal who has vascular similarity to humans
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