New technique to demonstrate the network of blood capillaries of the human retina in their three-dimensional arrangement

Fixation strategies for retinal immunohistochemistry

Immunohistochemical and ex vivo anatomical studies have provided many glimpses of the variety, distribution, and signaling components of vertebrate retinal neurons. The beauty of numerous images published to date, and the qualitative and quantitative information they provide, indicate that these approaches are fundamentally useful. However, obtaining these images entailed tissue handling and exposure to chemical solutions that differ from normal extracellular fluid in composition, temperature, and osmolarity. Because the differences are large enough to alter intercellular and intracellular signaling in neurons, and because retinae are susceptible to crush, shear, and fray, it is natural to wonder if immunohistochemical and anatomical methods disturb or damage the cells they are designed to examine. Tissue fixation is typically incorporated to guard against this damage and is therefore critically important to the quality and significance of the harvested data. Here, we describe mechanisms of fixation; advantages and disadvantages of using formaldehyde and glutaraldehyde as fixatives during immunohistochemistry; and modifications of widely used protocols that have recently been found to improve cell shape preservation and immunostaining patterns, especially in proximal retinal neurons.

Three dimensional analysis of the retinal vasculature using immunofluorescent staining and confocal laser scanning microscopy

AIM

To undertake a qualitative and quantitative analysis in three dimensions of the human retinal vasculature.

METHOD

Fixed and excised whole retinas were permeabilised and subjected to immunofluorescent staining for blood vessel components followed by confocal laser scanning microscopy. Single projection and stereoimages were constructed using computer software. XZ sections through the retina were constructed and the vasculature analysed using appropriate software.

RESULTS

Immunofluorescent staining with no discontinuities was present in vessels of all sizes, the confocal images of the capillary network being free of out of focus blur at all depths. Quantitative analysis of XZ sections confirmed the qualitative impression of sharp delineation of the deep retinal capillary plexus, an absence of laminar arrangement of capillaries within the inner retina, and a truncated cone of capillaries around the foveal avascular zone (FAZ) wherein the superficial capillaries approached the FAZ more closely than those in the deeper retina.

CONCLUSION

Immunofluorescent staining of the retina and confocal laser scanning microscopy were shown to be useful in analysing accurate three dimensional reconstructions of the normal retinal vasculature without affecting overall tissue architecture.

Three-dimensional structure of human retinal vessels studied by vascular casting

A new casting technique for studying the three-dimensional structure of the human retinal vascular system on post mortem tissue was developed. The technique was designed to provide an overview presentation of the retinal vasculature such that localized areas with vascular pathology could be identified for further analysis of three-dimensional structure. The paper presents qualitative characteristics of three-dimensional structure in the normal human retinal vascular bed, to provide a basis for future studies on vascular impairment in retinal disease.