Insights Into Microvasculature Topography And Its Coupling With Neuronal Demands In The Human Retina

Abstract

 

Purpose:

 

Retinal vascular diseases are a major cause of blindness worldwide. Retinal vulnerability to injury stems from the disparity between high neuronal energy demands and the limited blood supply available to retinal structures. It remains unclear how intra-retinal capillary organization is coupled to the heterogeneous configuration of neuronal metabolic activity between different retinal layers. This study provides important quantitative information concerning the topographical characteristics of retinal microvasculature, in relation to neurons, using our recently developed perfusion-fixation-staining technique in human cadaveric eyes.

 

Methods:

 

The macula-papillary region, 2mm nasal to the fovea, was studied in 14 undiseased human eyes (mean age 40 ± 6.1 years). Novel micropipette technology was used to cannulate the central retinal artery and label the retinal microcirculation using a Phalloidin perfusate. Co-localization of capillary networks within retinal layers was studied using anti-gamma-Synuclein, anti-Goalpha and anti-Parvalbumin antibodies; labeling for retinal ganglion cells (RGCs) and axons, ON bipolar cells and horizontal cells, respectively. Confocal microscopy based techniques were used to document topographic relationships between microvascular distribution and neuronal populations. Reproducible methodology was also employed to quantify capillary diameter, capillary density (expressed as percentage of tissue volume) and capillary loop area within retinal layers.

 

Results:

 

Laminar capillary networks were identified in the nerve fibre layer (NFL), the deep portion of the inner nuclear layer (INL) and outer plexiform layer. Complex three-dimensional networks were identified in the RGC layer and the superficial portion of the INL. Capillaries in the NFL were predominantly oriented parallel to the trajectory of RGC axons while consistent capillary-neuronal spatial relationships were not identified within remaining layers. Capillary density and loop area measurements were significantly different between retinal layers (both P < 0.05), however, regions of greatest capillary density and loop area did not correlate with previously demonstrated regions of high metabolic demand (density of 17.95% in INL vs 22.32% in RGC layer). There was no difference in capillary diameter between different layers (P > 0.05).

 

Conclusions:

 

There is significant disparity in capillary topography between retinal layers. Greatest capillary density does not correlate exactly with previously described regions of maximal neuronal energy consumption. These findings may have relevance to understanding novel patho-physiological mechanisms involved in retinal vascular diseases.

 

Keywords: retina • blood supply • immunohistochemistry