Radial peripapillary capillaries (RPCs) comprise a unique network of capillary beds within the retinal nerve fibre layer (RNFL) and play a critical role in satisfying the nutritional requirements of retinal ganglion cell (RGC) axons. Understanding the topographical and morphological characteristics of these networks through in vivo techniques may improve our understanding about the role of RPCs in RGC axonal health and disease. This study utilizes a novel, non-invasive and label-free optical imaging technique, speckle variance optical coherence tomography (svOCT), for quantitatively studying RPC networks in the human retina. Six different retinal eccentricities from 16 healthy eyes were imaged using svOCT. The same eccentricities were histologically imaged in 9 healthy donor eyes with a confocal scanning laser microscope. Donor eyes were subject to perfusion-based labeling techniques prior to retinal dissection, flat mounting and visualization with the microscope. Capillary density and diameter measurements from each eccentricity in svOCT and histological images were compared. Data from svOCT images were also analysed to determine if there was a correlation between RNFL thickness and RPC density. The results are as follows: (1) The morphological characteristics of RPC networks on svOCT images are comparable to histological images; (2) With the exception of the nasal peripapillary region, there were no significant differences in RPC density measurements between svOCT and histological images; (3) Capillary diameter measurements were significantly greater in svOCT images compared to histology; (4) There is a positive correlation between RPC density and RNFL thickness. The findings in this study suggest that svOCT is a reliable modality for analyzing RPC networks in the human retina. It may therefore be a valuable tool for aiding our understanding about vasculogenic mechanisms that are involved in RGC axonopathies. Further work is required to explore the reason for some of the quantitative differences between svOCT and histology.

The roles of the iris microvasculature have been increasingly recognised in the pathogenesis of glaucoma and cataract; however limited information exists regarding the iris microvasculature and its endothelium. This study quantitatively assessed the iris microvascular network and its endothelium using intra-luminal micro-perfusion, fixation, and staining of the porcine iris. The temporal long posterior ciliary artery of 11 isolated porcine eyes was cannulated, perfusion-fixed and labelled using silver nitrate. The iris microvasculature was studied for its distribution, orders and endothelial morphometrics. The density of three layers of microvasculature was measured. Endothelial cell length and width were measured for each vessel order. The iris has an unusual vascular distribution which consisted of abundant large vessels in the middle of the iris stroma, branching over a relatively short distance to the microvasculature located in the superficial and deep stroma as well as the pupil edge. The average vascular density of the middle, superficial, and deep layers were 38.9 ± 1.93%, 10.9 ± 1.61% and 8.0 ± 0.79% respectively. Multiple orders of iris vessels (capillary, 6 orders of arteries, and 4 orders of veins) with relatively large capillary and input arteries (319.5 ± 25.6 μm) were found. Significant heterogeneity of vascular diameter and shape of the endothelia was revealed in different orders of the iris vasculature. Detailed information of topography and endothelium of the iris microvasculature combined with unique structural features of the iris may help us to further understand the physiological and pathogenic roles of the iris in relevant ocular diseases.

Vascular comorbidities are inherently linked to the pathogenesis of central retinal artery occlusion (CRAO) and central retinal vein occlusion (CRVO). However, the endothelial-mediated pathogenic mechanisms that precede, and therefore modulate, luminal occlusion have not been clarified. The aim of this study was to delineate the pattern of endothelial morphometric alteration in the central retinal artery and vein in patients with vascular comorbidities. Eyes with a previous history of vascular occlusion were not included in this study in order to avoid the confounding effects of post-occlusion endothelial changes. This study also sought to determine if vascular comorbidities had a disparate effect on arterial and venous endothelium in the optic nerve head. Comparisons were made between 13 human eyes from patients with vascular comorbidities and 22 control eyes from patients with no known systemic disease. Novel micro-cannulation techniques developed in our laboratory were used to label the cytoskeleton and nuclei of endothelial cells in the central retinal artery and vein following which images were captured using confocal microscopy. Endothelial and nuclear morphometric parameters were quantified in different laminar regions of the optic nerve head. F-actin stress fibre expression was also quantified. Analysis of covariance was used to determine statistical differences between the two groups. Interestingly, age did not influence endothelial morphometry, nuclear morphometry or f-actin expression in central retinal vessels. There were also no arterial endothelial differences between control and disease groups in any laminar region. Endothelial f-actin stress fibre expression increased significantly in the central retinal vein in patients with vascular comorbidities. The greatest change in these eyes was found to occur at the posterior lamina cribrosa. Increased venous endothelial f-actin stress fibre expression may reflect vascular comorbid disease-induced alterations to hemodynamic properties and coagulation cascades in the central retinal vein. The posterior lamina may be an important site for thrombus formation in CRVO as venous endothelia in this region are most influenced by the presence of vascular comorbidities. The findings of this study suggest that the role of endothelial dysfunction in CRVO and CRAO pathogenesis could be different.

New and more precise subretinal surgical techniques would be useful in a range of retinal diseases. The purpose of this study is to determine the feasibility of using fiberoptically delivered ultraviolet laser energy to transect or ablate subretinal tissues. Choroid segments dissected from fresh porcine eyes, with or without the retinal pigment epithelium (RPE), were clamped in a fluid bath. Pulsed fourth harmonic (266 nm) of a Nd:YAG laser radiation was delivered via an optical fiber probe at fluence levels between 0.08 and 0.40 J/cm(2). The tissue was then fixed and sectioned for histological examination. Radiation induced damage was categorized by the degree of tissue disruption and ablation depth. Tissue ablation and the severity of the tissue injury varied with both tissue properties and applied laser parameters. Disruption of Bruch's membrane was typically induced by 10 pulses of 0.30 J/cm(2) or 2 pulses of 0.40 J/cm(2). Lower radiation doses did not disrupt Bruch's membrane, but did damage the choroidal tissue and produce vacuoles in the underlying choroid. The full thickness of the choroid was ablated by 200 pulses of 0.40 J/cm(2). The presence of the RPE produced a shielding effect which was greater than would be expected for an equivalent thickness of choroidal tissue. Ablation characteristics of subretinal tissue are highly dependent on the laser parameters used and the type of tissue involved. To perform well controlled laser surgery on subretinal tissues both laser parameters and the properties of the target cells and tissues have to be considered.

The purpose of this study was to determine posture-induced changes in arterial blood pressure (ABP), intraocular pressure (IOP), orbital pressure (Porb), intracranial pressure (ICP), and jugular vein pressure (JVP) at various tilt angles in an in vivo pig.