Aqueous humor as eye lymph: A crossroad between venous and lymphatic system.

Aqueous humor (AQH) is a transparent fluid with characteristics similar to those of the interstitial fluid, which fills the eyeball posterior and anterior chambers and circulates in them from the sites of production to those of drainage. The AQH volume and pressure homeostasis is essential for the trophism of the ocular avascular tissues and their normal structure and function. Different AQH outflow pathways exist, including a main pathway, quite well defined anatomically and referred to as the conventional pathway, and some accessory pathways, more recently described and still not fully morphofunctionally understood, generically referred to as unconventional pathways. The conventional pathway is based on the existence of a series of conduits starting with the trabecular meshwork and Schlemm's Canal and continuing with a system of intrascleral and episcleral venules, which are tributaries to veins of the anterior segment of the eyeball. The unconventional pathways are mainly represented by the uveoscleral pathway, in which AQH flows through clefts, interstitial conduits located in the ciliary body and sclera, and then merges into the aforementioned intrascleral and episcleral venules. A further unconventional pathway, the lymphatic pathway, has been supported by the demonstration of lymphatic microvessels in the limbal sclera and, possibly, in the uvea (ciliary body, choroid) as well as by the ocular glymphatic channels, present in the neural retina and optic nerve. It follows that AQH may be drained from the eyeball through blood vessels (TM-SC pathway, US pathway) or lymphatic vessels (lymphatic pathway), and the different pathways may integrate or compensate for each other, optimizing the AQH drainage. The present review aims to define the state-of-the-art concerning the structural organization and the functional anatomy of all the AQH outflow pathways. Particular attention is paid to examining the regulatory mechanisms active in each of them. The new data on the anatomy and physiology of AQH outflow pathways is the key to understanding the pathophysiology of AQH outflow disorders and could open the way for novel approaches to their treatment.

Evaluation of neural innervation in the human conventional outflow pathway distal to Schlemm's canal.

The distal outflow pathway of the human eye consists of the outer wall of Schlemm's canal, collector channels, and the deep-scleral, mid-scleral and episcleral vessels. It is the last region of transit for aqueous humor before returning to the venous system. While the trabecular meshwork, scleral spur, and inner wall of Schlemm's canal have been extensively analyzed to define their contributions to aqueous outflow, the role of the distal outflow pathway is not completely understood. Collector channels, emanating from Schlemm's canal were previously thought to be passive conduits for aqueous humor. However, recent studies have shown many collector channels contain flap-like appendages which move with changes in pressure. These findings, along with studies demonstrating innervation of episcleral vessels, have led to questions regarding whether other structures in the distal outflow pathway are under neural regulation and how this may influence aqueous humor outflow. This study evaluates the innervation of the outer wall of Schlemm's canal and collector channels, along with the deep-scleral, mid-scleral and episcleral vasculature with microcomputed tomography and 3-dimensional reconstruction, correlative light microscopy, immunohistochemistry, and transmission electron microscopy. Peripheral, autonomic, and sensory nerve fibers were found to be present adjacent to Schlemm's canal outer wall endothelium, collector channel endothelium, and in the different regions of the distal outflow vasculature. Nerves were more commonly identified in regions that contained collector channels when compared to regions without collector channels. These findings regarding the neural anatomy suggest an active neural regulation of aqueous humor outflow throughout the proximal and distal regions of the conventional outflow pathway.

RELATIONSHIP BETWEEN MYOPIC CHOROIDAL NEOVASCULARIZATION ACTIVITY AND PERFORATING SCLERAL VESSELS IN HIGH MYOPIA.

PURPOSE: To study perforating scleral vessels (PSVs) in patients with high myopia using swept-source optical coherence tomography and to determine their relationship with myopic choroidal neovascularization (mCNV) and its activity. METHODS: Retrospective analysis of patients with high myopia (≥-6 D or ≥26 mm of axial length) using multimodal imaging. The presence of PSVs and mCNV was assessed using swept-source optical coherence tomography images (TRITON; Topcon Corporation, Japan). RESULTS: Five hundred sixty-four eyes from 297 highly myopic patients were studied. One hundred fifty-five eyes (27.5%) showed signs of mCNV while PSVs were found in 500 eyes (88.6%). Perforating scleral vessels were found in 93.5% (145/155) of eyes with mCNV, and they were under or in contact with the mCNV in 80.6% (117/145). The mean number of intravitreal injections received by patients with mCNV was 4.06 ± 4.17 along 66.9 ± 4.1 months of follow-up. The number of injections per year was 1.32 ± 1.56, the mean number of relapses was 1.11 ± 1.83, and the mean number of relapses per year was 0.25 ± 0.41. CONCLUSION: Perforating scleral vessels are more common among highly myopic patients suffering from neovascular complications. Myopic CNV complexes that are coincident with PSVs on optical coherence tomography show higher rates of activity, needing more injections to control them and being more prone to relapses.

Nanoencapsulated hybrid compound SA-2 with long-lasting intraocular pressure-lowering activity in rodent eyes.

Purpose: Glaucoma is a neurodegenerative disease of the eye with an estimated prevalence of more than 111.8 million patients worldwide by 2040, with at least 6 to 8 million projected to become bilaterally blind. Clinically, the current method of slowing glaucomatous vision loss is to reduce intraocular pressure (IOP). In this manuscript, we describe the in vitro cytoprotective and in vivo long lasting IOP-lowering activity of the poly D, L-lactic-co-glycolic acid (PLGA) nanoparticle-encapsulated hybrid compound SA-2, possessing nitric oxide (NO) donating and superoxide radical scavenging functionalities. Methods: Previously characterized primary human trabecular meshwork (hTM) cells were used for the study. hTM cells were treated with SA-2 (100 µM, 200 µM, and 1,000 µM), SA-2 PLGA-loaded nanosuspension (SA-2 NPs, 0.1%), or vehicle for 30 min. Cyclic guanosine monophosphate (cGMP) and super oxide dismutase (SOD) levels were analyzed using commercial kits. In another experiment, hTM cells were pretreated with tert-butyl hydrogen peroxide (TBHP, 300 µM) for 30 min followed by treatment with escalating doses of SA-2 for 24 h, and CellTiter 96 cell proliferation assay was performed. For the biodistribution study, the cornea, aqueous humor, vitreous humor, retina, choroid, and sclera were collected after 1 h of administration of a single eye drop (30 µl) of SA-2 NPs (1% w/v) formulated in PBS to rat (n = 6) eyes. Compound SA-2 was quantified using high performance liquid chromatography /mass spectrometry (HPLC/MS). For the IOP-lowering activity study, a single SA-2 NPs (1%) eye drop was instilled in normotensive rats eyes and in the IOP-elevated rat eyes (n = 3/group, in the Morrison model of glaucoma), or Ad5TGFß2-induced ocular hypertensive (OHT) mouse eyes (n = 5/group). IOP was measured at various time points up to 72 h, and the experiment was repeated in triplicate. Mouse aqueous humor outflow facility was determined with multiple flow-rate infusion and episcleral venous pressure estimated with manometry. Results: SA-2 upregulated cGMP levels (six- to ten-fold) with an half maximal effective concentration (EC50) of 20.3 µM in the hTM cells and simultaneously upregulated (40-fold) the SOD enzyme when compared with the vehicle-treated hTM cells. SA-2 also protected hTM cells from TBHP-induced decrease in cell survival with an EC50 of 0.38 µM. A single dose of slow-release SA-2 NPs (1% w/v) delivered as an eye drop significantly lowered IOP (by 30%) in normotensive and OHT rodent eyes after 3 h post-dose, with the effect lasting up to 72 h. A statistically significant increase in aqueous outflow facility and a decrease in episcleral venous pressure was observed in rodents at this dose at 54 h. Conclusions: Hybrid compound SA-2 upregulated cGMP in hTM cells, increased outflow facility and decreased IOP in rodent models of OHT. Compound SA-2 possessing an antioxidant moiety provided additive cytoprotective activity to oxidatively stressed hTM cells by scavenging reactive oxygen species (ROS) and increasing SOD enzyme activity. Additionally, the PLGA nanosuspension formulation (SA-2 NPs) provided longer duration of IOP-lowering activity (up to 3 days) in comparison with the free non-encapsulated SA-2 drug. The data have implications for developing novel, non-prostaglandin therapeutics for IOP-lowering and cytoprotective effects with the possibility of an eye drop dosing regimen of once every 3 days for patients with glaucoma.

Episcleral venous pressure response to brain stem stimulation: Effect of topical lidocaine.

Episcleral venous pressure (EVP) is important for steady state intraocular pressure (IOP), as it has to be overcome by aqueous humor in order to leave the eye. Recent evidence suggests a neuronal tone being present, as topical anesthesia lowered EVP. The superior salivatory nucleus in the brainstem could be identified to elicit increases in EVP during electrical stimulation. In the present study the effect of topical anesthesia on the stimulation effect was investigated. 8 Spraque Dawley rats were anesthetized, artificially ventilated with CO2 monitoring and continuous blood pressure monitoring. Intraocular pressure was measured continuously through a cannula in the vitreous body. Episcleral venous pressure was measured by direct cannulation of an episcleral vein via a custom made glass pipette connected to a servonull micropressure system. Electrical stimulation of the superior salivatory nucleus (9 µA, 200 pulses of 1 ms duration) increased EVP from 8.51 ± 1.82 mmHg to 10.97 ± 1.93 mmHg (p = 0.004). After application of topical lidocaine EVP increased from 7.42 ± 1.59 mmHg to 9.77 ± 1.65 mmHg (p = 0.007). The EVP response to stimulation before and after lidocaine application was not statistically significantly different (2.45 ± 0.5 vs 2.35 ± 0.49 mmHg, p = 0.69), while the decrease in baseline EVP was (8.51 vs. 7.42 mmHg, p = 0.045). The present data suggest that distinct neuronal mechanisms controlling the episcleral circulation of rats exist. This is in keeping with previous reports of two distinct arterio-venous anastomoses, one in the limbal circulation and one in the conjunctival/episcleral circulation.

PPARγ modulates refractive development and form deprivation myopia in Guinea pigs.

Form deprivation myopia (FDM) is characterized by loss of choroidal thickness (ChT), reduced choroidal blood perfusion (ChBP), and consequently scleral hypoxia. In some tissues, changes in levels of peroxisome proliferator-activated receptor γ (PPARγ) expression modulate hypoxia-induced pathological responses. We determined if PPARγ modulates FDM through changes in ChT, ChBP, scleral hypoxia-inducible transcription factor (HIF-1α) that in turn regulate scleral collagen type 1 (COL1) expression levels in guinea pigs. Myopia was induced by occluding one eye, while the fellow eye served as control. They received daily peribulbar injections of either the PPARγ antagonist GW9662, or the GW1929 agonist, with or without ocular occlusion for 4 weeks. Ocular refraction and biometric parameters were estimated at baseline, 2 and 4 weeks post-treatment. ChT and ChBP were measured at the 2- and 4-week time points. Western blot analysis determined the expression levels of scleral HIF-1α and COL1. GW9662 induced a myopic shift in unoccluded eyes. Conversely, GW1929 inhibited FDM progression without affecting the refraction in unoccluded eyes. GW9662 reduced both ChT and ChBP in unoccluded eyes, while GW1929 inhibited their declines in occluded eyes. Scleral HIF-1α expression rose in GW9662-treated unoccluded eyes whereas GW1929 reduced HIF-1α upregulation in occluded eyes. GW9662 downregulated scleral COL1 expression in unoccluded eyes, while GW1929 reduced their decreases in occluded eyes. Therefore, PPARγ modulates collagen expression levels and FDM through an inverse relationship between changes in PPARγ and HIF-1α expression levels.

Scleral hypoxia is a target for myopia control.

Worldwide, myopia is the leading cause of visual impairment. It results from inappropriate extension of the ocular axis and concomitant declines in scleral strength and thickness caused by extracellular matrix (ECM) remodeling. However, the identities of the initiators and signaling pathways that induce scleral ECM remodeling in myopia are unknown. Here, we used single-cell RNA-sequencing to identify pathways activated in the sclera during myopia development. We found that the hypoxia-signaling, the eIF2-signaling, and mTOR-signaling pathways were activated in murine myopic sclera. Consistent with the role of hypoxic pathways in mouse model of myopia, nearly one third of human myopia risk genes from the genome-wide association study and linkage analyses interact with genes in the hypoxia-inducible factor-1α (HIF-1α)-signaling pathway. Furthermore, experimental myopia selectively induced HIF-1α up-regulation in the myopic sclera of both mice and guinea pigs. Additionally, hypoxia exposure (5% O2) promoted myofibroblast transdifferentiation with down-regulation of type I collagen in human scleral fibroblasts. Importantly, the antihypoxia drugs salidroside and formononetin down-regulated HIF-1α expression as well as the phosphorylation levels of eIF2α and mTOR, slowing experimental myopia progression without affecting normal ocular growth in guinea pigs. Furthermore, eIF2α phosphorylation inhibition suppressed experimental myopia, whereas mTOR phosphorylation induced myopia in normal mice. Collectively, these findings defined an essential role of hypoxia in scleral ECM remodeling and myopia development, suggesting a therapeutic approach to control myopia by ameliorating hypoxia.

The effects of negative periocular pressure on intraocular pressure.

Glaucoma is a major cause of blindness, and IOP reduction remains the only clinically-validated therapy. In this study, we analyze a novel IOP-lowering strategy that uses a modest negative pressure (vacuum) applied locally to the periorbital region by a pair of goggles with each lens individually connected to a programmable pump. Motivated by clinical data showing an IOP reduction, we used an existing validated lumped-parameter model of the eye to understand the putative mechanism of this treatment. The model considers aqueous humor dynamics, episcleral venous pressure, and changes in ocular blood volume to describe how IOP changes with time in response to an external perturbation. We find that clinical data are qualitatively and quantitatively consistent with model predictions if we include two primary mechanisms in the model: first, negative pressure application causes a relatively rapid increase in globe volume accompanied by increased blood volume in the eye. Second, negative pressure application reduces episcleral venous pressure, causing a slower adjustment of IOP due to altered aqueous humor dynamics. These results provide testable hypotheses that hopefully will lead to a fuller experimentally-driven understanding of how negative periocular pressure influences IOP. Evaluating the long-term effects of such treatments on glaucoma patients requires further clinical study.

Effects of topical erythropoietin on healing experimentally-induced avascular scleral damage in a rabbit model.

The present study was designed to investigate the effect of topical erythropoietin on the healing process of induced necrotizing scleritis and to evaluate the ocular side effects of this treatment modality in a rabbit model. Necrotizing scleritis was induced in 8 New Zealand albino rabbits. The animals were then randomly divided into one of two groups: a treated group administered a topical erythropoietin-containing cellulose-based gel every 8 h or a control group treated with a cellulose-based gel without erythropoietin every 8 h. The sizes of the lesions measured at different time points were compared between the groups. After three months, the rabbits' eyes were enucleated and histologically and immunohistochemically evaluated for angiogenesis and apoptosis. The lesions were completely vascularized in all eyes of the treated group and 50% of eyes of the control group. The mean interval from the induction of scleral necrosis to a complete improvement was 28 days in the treated group and 62.5 days in the control group (P = 0.04). Histological examination revealed that erythropoietin enhanced the improvement of necrotizing scleritis by stimulating angiogenesis and reducing apoptosis. Neovascularization of the cornea, iris, or retina was not observed in the treated group. We observed a significantly faster recovery to complete improvement of necrotizing scleritis in rabbit eyes treated with erythropoietin compared to those of the control group. Treated eyes had a higher rate of complete healing and had no ocular safety concerns. This therapeutic modality represents a promising treatment for scleral necrosis following various types of ocular surgery.

Dose-dependent effects of netarsudil, a Rho-kinase inhibitor, on the distal outflow tract.

PURPOSE: To characterize the effects of netarsudil on the aqueous humor outflow tract distal to the trabecular meshwork (TM). We hypothesized that netarsudil increases outflow facility in eyes with and without circumferential ab interno trabeculectomy (AIT) that removes the TM. METHODS: Sixty-four porcine anterior segment cultures were randomly assigned to groups with (n = 32) and without circumferential AIT (n = 32). Cultures were exposed to 0.1, 1, and 10 µM netarsudil (N = 8 eyes per concentration). For each concentration, IOP and vessel diameters were compared with their respective pretreatment baselines. Outflow tract vessel diameters were assessed by spectral-domain optical coherence tomography (SDOCT) and rendered in 4D (XYZ time series). RESULTS: Netarsudil at 1 µM reduced IOP both in eyes with TM (- 0.60 ± 0.24 mmHg, p = 0.01) and in eyes without TM (- 1.79 ± 0.42 mmHg, p < 0.01). At this concentration, vessels of the distal outflow tract dilated by 72%. However, at 0.1 µM netarsudil elevated IOP in eyes with TM (1.59 ± 0.36 mmHg, p < 0.001) as well as in eyes without TM (0.23 ± 0.32 mmHg, p < 0.001). Vessels of the distal outflow tract constricted by 31%. Similarly, netarsudil at a concentration of 10 µM elevated IOP both in eyes with TM (1.91 ± 0.193, p < 0.001) and in eyes without TM (3.65 ± 0.86 mmHg, p < 0.001). At this concentration, outflow tract vessels constricted by 27%. CONCLUSION: In the porcine anterior segment culture, the dose-dependent IOP changes caused by netarsudil matched the diameter changes of distal outflow tract vessels. Hyper- and hypotensive properties of netarsudil persisted after TM removal.

[Strengthening the understanding of the pathological evolution of myopia].

The concern of high myopia in adolescents is increasingly prominent, because of the high prevalence and early onset of myopia in younger children. High myopia increases the risk of various fundus complications, resulting in serious damage to the vision of the working population. The mechanisms underlying the fundus pathology in high myopia remain unknown, although some studies have indicated the initial thinning of the choroid during the myopia progression might count a lot. The thinning of the choroid would influence the blood supply of the retina and sclera and accelerate the progression of myopia to high myopia, inducing the pathologic changes of the fundus. Since the treatment for pathological myopia is limited and cannot reverse the already existed visual impairment, preventive measures are necessary, including the attempts to delay the onset of myopia, to retard progression from mild myopia to high myopia and to retard the pathological changes of high myopia. Future researches should strengthen the understanding of the characteristics of pathologic changes of myopia, establish a predictive index system and a health management system to monitor early pathological changes, and promote early detection and intervention, so as to prevent fundus complications related to high myopia in multiple ways and avoid blindness and visual impairment caused by pathological fundus changes of myopia. (Chin J Ophthalmol, 2019, 55:721-725).

THREE-DIMENSIONAL ANALYSIS OF SUBMACULAR PERFORATING SCLERAL VESSELS BY ENHANCED DEPTH IMAGING OPTICAL COHERENCE TOMOGRAPHY.

PURPOSE: To analyze submacular perforating scleral vessels (PSVs) using enhanced depth imaging spectral domain optical coherence tomography (EDI-SDOCT). METHODS: Twenty-two eyes of 11 healthy women were included in this retrospective study. Central EDI-SDOCT scans (3 × 4.5 × 1.9 mm, 13.5 mm scan area) were acquired and postprocessed by denoising, manual sclera segmentation, and PSV investigated by five graders. RESULTS: Mean age was 22.4 ± 6.2 years. Mean refractive error was -0.44 ± 0.8 diopters. Mean axial length was 23.08 ± 0.63 mm. The coefficient of agreement for grading was good. Mean number of submacular PSVs was 0.33 ± 0.2 per mm (range from 0 to 9 per eye). Subfield analysis showed 0.2 ± 0.5 (range 0-2) and 2.1 ± 1.8 (range 0-7) vessels, respectively, for central 1-mm diameter and 3-mm diameter. Quadrant analysis showed 0.7 ± 0.9, 0.5 ± 0.9, 0.3 ± 0.6, and 0.4 ± 0.6 vessels, respectively for superior, inferior, nasal, and temporal quadrants. Total number of PSV showed no significant side difference (median difference 0.5, confidence interval -3.0 to 3.0, P = 0.94) or an influence of axial length (P = 0.16). CONCLUSION: This is the first description of three-dimensional EDI-SDOCT visualization of submacular PSV in healthy eyes. This method allows for in vivo imaging of a critical component of outer retinal perfusion at the posterior pole.

Advanced glaucoma secondary to bilateral idiopathic dilated episcleral veins - a case report.

BACKGROUND: Idiopathic elevated episcleral venous pressure (IEEVP) or idiopathic dilated episcleral veins (IDEV) is a rare abnormality, and thus therapeutic treatment for this condition rarely is discussed. We report a case of a patient with bilateral glaucoma secondary to IDEV for whom intraocular pressures (IOPs) were controlled successfully by trabeculectomy. CASE PRESENTATION: A 50 year-old female with a complaint of persistent red eyes for over 30 years, presented with numerous tortuous and engorged episcleral vessels in both eyes (OU), open angles OU with spontaneous blood in Schlemm's canal 360 degrees bilaterally. Orbital color Doppler examination showed the superior ophthalmic veins to be of normal calibre, with no reversal of flow. Head MRI with contrast and cerebral angiography were negative for arteriovenous fistula. Coronary angiography, color Doppler echocardiography and chest radiographs were within normal limits. A diagnosis of secondary glaucoma and IDEV was made. Neither anti-glaucoma medications, nor laser trabeculoplasty reduced the patent's IOP effectively. Only after trabeculectomy was performed in each eye, were IOPs successfully controlled. CONCLUSIONS: This case serves to remind clinicians of the importance of identifying and evaluating thoroughly patients with episcleral vessel dilation in non-inflamed eyes with no known cause. A misdiagnosis or missed diagnosis of long-term elevated intraocular pressure may result in significant damage to the optic nerve. In addition, when performing filtration surgery it is crucial that the ophthalmologist control the IOP and make an effort to prevent choroidal effusion.

Bimatoprost sustained-release intracameral implant reduces episcleral venous pressure in dogs.

OBJECTIVE: To determine the effect of a bimatoprost sustained-release intracameral implant (Bimatoprost SR) on episcleral venous pressure (EVP) in normal dogs. METHODS: Normotensive beagle dogs were randomized to receive Bimatoprost SR 30 µg (n = 7) or sham injection (needle insertion only, n = 7) in one eye on day 1. EVP was measured with an episcleral venomanometer through day 65. Episcleral aqueous outflow vessels were identified using fluorescence imaging following intracameral injection of indocyanine green in one additional animal. A separate cohort of dogs that had been trained for conscious intraocular pressure (IOP) measurements received Bimatoprost SR 30 µg (n = 8) in one eye; IOP was evaluated through day 66. RESULTS: Baseline mean EVP was 10.0 mmHg in the Bimatoprost SR group and 10.4 mmHg in the sham group. Eyes treated with Bimatoprost SR exhibited a transient increase in mean EVP that peaked at day 8, followed by a decrease to levels below baseline. From day 29 to day 65, the change in mean EVP from baseline ranged from -2.4 to -3.9 mmHg (P < 0.05 vs. sham). Baseline mean IOP in eyes treated with Bimatoprost SR was 14.9 mmHg, and a steady IOP reduction was maintained through day 66. Bimatoprost SR-treated eyes exhibited a selective, sustained dilation of aqueous outflow vessels that was not observed in sham-treated eyes. CONCLUSIONS: In normal dogs, Bimatoprost SR was associated with a transient increase in EVP followed by a sustained decrease. Changes in EVP were accompanied by a sustained dilation of aqueous outflow vessels.

Visual impairment by multiple vascular embolization with hydroxyapatite particles.

We demonstrate a case of ocular impairment caused by a hydroxyapatite filler injection and review the prior literature on clinical presentations. A healthy woman, who received a hydroxyapatite filler injection into the glabella for nose augmentation suddenly had symptoms of nausea, diplopia, visual loss in the left eye, and impaired consciousness. Her left eye showed paresis of the inferior branch of the oculomotor nerve, conjunctival injection, cell infiltration in the anterior chamber, and multiple white spots in the nasal fundus. Purpura was detected in the area from the glabella to the left forehead. An orbital computed tomography (CT) scan demonstrated high-density deposits along vessels in the left medial orbit and forehead. Although her consciousness stabilized after a few days, the vision in her left eye deteriorated due to corneal edema and both hypopyon and hyphema in the anterior chamber, and the skin from the glabella to the left forehead developed necrosis. Multiple plaques were observed within the conjunctival and scleral vessels. After 2 months, diplopia and visual loss issues were mostly resolved. A histological examination of the conjunctiva specimen showed multiple foreign bodies plugged vessels that could be dissolved by decalcification. Recently, the number of complications by cosmetic filler injections has increased. The migrated hydroxyapatite particles in vessels cause multiple vascular emboli that can lead to various symptoms.

Aqueous Angiography in Living Nonhuman Primates Shows Segmental, Pulsatile, and Dynamic Angiographic Aqueous Humor Outflow.

PURPOSE: To evaluate the feasibility of safely performing aqueous angiography in intact eyes of living nonhuman primates (NHPs) for evaluating aqueous humor outflow and segmental patterns. DESIGN: Cross-sectional, observational study. SUBJECTS: Six nonhuman primates. METHODS: Aqueous angiography was performed in 6 nonhuman primates. After anesthesia, an anterior chamber (AC) maintainer was placed through a temporal 1-mm side-port wound. Indocyanine green (ICG; 0.4%) or 2.5% fluorescein was introduced (individually or in sequence) into the eye with a gravity-driven constant-pressure system. Aqueous angiography images were obtained with a Spectralis HRA+OCT (Heidelberg Engineering GmbH, Heidelberg, Germany) suspended over the NHP eye using a custom-designed surgical boom arm. Concurrent anterior segment optical coherence tomography (OCT) was performed on distally angiographically positive and negative regions. MAIN OUTCOME MEASURES: Angiographic patterns described by location, time-course, choice of tracer, and anterior-segment OCT. RESULTS: Aqueous angiography in the living NHP eye demonstrated mostly stable angiographic patterns. With multimodal imaging, angiographically positive signal co-localized with episcleral veins as identified by infrared imaging and intrascleral lumens, as demonstrated by anterior segment OCT. Sequential aqueous angiography in individual eyes with ICG followed by fluorescein showed similar angiographic patterns. A pulsatile nature of aqueous angiographic outflow was sometimes observed. Aqueous angiographic patterns could also dynamically change. In some instances, positive angiographic flow suddenly arose in regions previously without an angiographic signal. Alternatively, an angiographic signal could suddenly disappear from regions in which an angiographic signal was initially documented. CONCLUSIONS: Aqueous angiography in living NHPs demonstrated segmental and pulsatile patterns with a newly described ability to dynamically shift. These characteristics further the understanding of live aqueous humor outflow biology and may be useful in improving glaucoma surgeries aimed at trabecular meshwork bypass.

Vascular endothelial growth factor signaling affects both angiogenesis and osteogenesis during the development of scleral ossicles.

Intramembranous ossification is a complex multi-step process which relies on extensive interactions among bone cells and surrounding tissues. The embryonic vasculature is essential in regulating endochondral ossification; however, its role during intramembranous ossification remains poorly understood, and in vivo studies are lacking. Previous research from our lab on the development of the intramembranous scleral ossicles has demonstrated an intriguing pattern of vascular development in which the areas of future osteogenesis remain avascular until after bone induction has occurred. Such avascular zones are located directly beneath each of the conjunctival papillae, epithelial structures which provide osteogenic signals to the underlying mesenchyme. Here we provide a high-resolution map of the developing vasculature from the time of ossicle induction to mineralization using a novel technique. We show that vegfa is expressed by the papillae and nearby mesenchymal tissue throughout HH 34-37, when vascular growth is taking place, and is down-regulated thereafter. Localized inhibition of Vegf results in expansion of the avascular zone surrounding the implanted papilla and mispatterning of the scleral ossicles. These results demonstrate that Vegf signaling could provide important insights into the complex relationship between bone and vasculature during intramembranous bone development.