Ciliary blood flow and aqueous humor production

Enhanced Intrusion of Exogenous Airborne Fine Particles toward Eyes in Humans and Animals: Where Damaged Blood-Ocular Barrier Plays a Crucial Role

Emerging data suggest a close correlation between ambient fine particle (AFP) exposure and eye disorders and pinpoint potential threats of AFPs to eye health in humans. However, the possible passage (including direct intrusion) and the interactions of AFPs with the eye microenvironment in addition to morphological and physiological injuries remain elusive. To this end, the likely transport of AFPs into the eyes via blood-ocular barrier (BOB) in humans and animals was investigated herein. Exogenous particles were recognized inside human eyes with detailed structural and chemical fingerprints. Importantly, comparable AFPs were found in sera with constant structural and chemical fingerprints, hinting at the translocation pathway from blood circulation into the eye. Furthermore, we found that the particle concentrations in human eyes from patients with diabetic retinopathy were much higher than those from patients with no fundus pathological changes (i.e., myopia), indicating that the damaged BOB increased the possibility of particle entrance. Our diseased animal model further corroborated these findings. Collectively, our results offer a new piece of evidence on the intrusion of exogenous particles into human eyes and provide an explanation for AFP-induced eye disorders, with substantially increased risk in susceptible individuals with BOB injuries.

Trace Element Concentration in the Blood and Aqueous Humor of Subjects with Eye Cataract

Cataract, characterized by the opacification of the lens, is the leading cause of reversible blindness and visual impairment globally. The study aims to investigate the role of trace elements such as Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn in the development and severity of cataract. Elements were quantified by inductively coupled plasma mass spectrometry in blood and aqueous humor of 32 cataract cases and 27 controls living in the Latium region, Italy. The association between element concentration in blood and aqueous humor and cataract severity, gender, and age of subjects were also assessed. Results showed Cr levels significantly elevated in both blood and aqueous humor of cataract cases, with concentrations that increased with cataract severity. In addition, blood Pb levels were significantly higher in older cases and positively correlated with the age of cataract cases, while blood Co and Cu levels negatively correlated with cataract severity, suggesting changes in the levels of these elements. In conclusion, this study provides evidence of the involvement of specific elements in cataract development and severity, and the findings highlighted important avenues for future research. Understanding the biological mechanism underlying element-induced cataract may contribute to preventing cataractogenesis and providing targeted interventions.

Hypotony in uveitis: an overview of medical and surgical management

Hypotony is a well-recognised, sight-threatening complication of uveitis. It can also be the final common endpoint for a multitude of disease entities. Multiple mechanisms underlie hypotony, and meticulous clinical history alongside ocular phenotyping is necessary for choosing the best intervention and therapeutic management. In this narrative review, a comprehensive overview of medical and surgical treatment options for the management of non-surgically induced hypotony is provided. Management of ocular hypotony relies on the knowledge of the aetiology and mechanisms involved. An understanding of disease trajectory is vital to properly educate patients. Both anatomical and functional outcomes depend on the underlying pathophysiology and choice of treatment.

Simulation of gravity- and pump-driven perfusion techniques for measuring outflow facility of ex vivo and in vivo eyes

Aqueous humor dynamics are commonly assessed by infusing fluid into the eye and measuring intraocular pressure (IOP). From the pressure-flow relationship, conventional outflow facility is estimated to study glaucomatous processes that lower facility or identify therapeutics that enhance facility in hopes of restoring healthy IOP levels. The relative merits and limitations of constant flow (CF), gravity-driven constant pressure (CPg), and pump-driven constant pressure (CPp) infusion techniques were explored via simulations of a lumped parameter viscoelastic model of the eye. Model parameter values were based on published perfusion system properties and outflow facility data from rodents. Step increases in pressure or flow were simulated without and with IOP noise recorded from enucleated eyes, anesthetized animals, and conscious animals. Steady-state response levels were determined using published window and ratio criteria. Model simulations show that all perfusion techniques estimate facility accurately and that ocular fluid dynamics set a hard limit on how fast measurements can be taken. This limit can be approached with CPg and CPp systems by increasing their gain but not with CF systems, which invariably take longest to settle. Facility experiment duration is further lengthened by inclusion of IOP noise, and data filtering is needed for steady-state detection with in vivo noise. The ratio criterion was particularly affected because noise in the flow data is amplified by the higher gain of CPg and CPp systems. A recursive regression method is introduced, which can ignore large transient IOP fluctuations that interfere with steady-state detection by fitting incoming data to the viscoelastic eye model. The fitting method greatly speeds up data collection without loss of accuracy, which could enable outflow facility measurements in conscious animals. The model may be generalized to study response dynamics to fluid infusion in other viscoelastic compartments of the body and model insights extended to optimize experiment design.

Targeting circular RNA-Glra2 alleviates retinal neurodegeneration induced by ocular hypertension

Glaucoma is a leading cause of irreversible vision loss characterized by retinal neurodegeneration. Circular RNAs (circRNAs) have emerged as the potential biomarkers and therapeutic targets for neurodegenerative diseases. However, the expression profiling of circRNAs in glaucomatous neurodegeneration has not been fully understood. In this study, we built a glaucomatous neurodegeneration model via the injection of microbeads into anterior chamber. circRNA expression profile and bioinformatics analysis revealed that compared with normal retinas, 171 circRNAs were dysregulated in the glaucomatous retinas, including 101 up-regulated circRNAs and 70 down-regulated circRNAs. Detecting the level of circular RNA-glycine receptor α2 subunit gene (cGlra2) in aqueous humor made it possible to distinguish glaucoma patients from cataract patients. Silencing of cGlra2 protected against oxidative stress- or hydrostatic pressure-induced retinal ganglion cell (RGC) injury in vitro. Moreover, silencing of cGlra2 retarded ocular hypertension-induced retinal neurodegeneration in vivo as shown by increased TUJ1 staining, reduced reactive gliosis, decreased retinal cell apoptosis, enhanced visual acuity, and improved retinal function. cGlra2 acted as a miRNA sponge to regulate RGC function through cGlra2/miR-144/BCL2L11 signaling axis. Collectively, this study provides novel insights into the underlying mechanism of retinal neurodegeneration and highlights the potential of cGlra2 as a target for the diagnosis and treatment of glaucoma.

Uveal vascular bed in health and disease: uveal vascular bed anatomy. Paper 1 of 2

The uveal vascular bed is the largest vascular system in the eye and has a role in supplying almost every tissue in the eyeball. This makes it the most important ocular vascular system. This is an up-to-date review of the literature of the entire uveal vascular bed in health based on detailed anatomy of the posterior ciliary arteries (PCAs), anterior ciliary arteries, cilioretinal arteries, and vortex veins. Although postmortem injection cast preparations gave us useful information on the morphology of the choroidal vascular bed; in vivo studies showed that they misled us for centuries about the in vivo situation. According to the postmortem cast studies, the uveal vascular bed has no segmental distribution, the uveal vessels anastomose freely with one another, there are inter-arterial and arteriovenous anastomoses in the choroid, and the choriocapillaris form a freely communicating and an uninterrupted vascular bed in the entire choroid.

Imaging ocular water inflow in the mouse with deuterium oxide MRI

Abnormal intraocular fluid flow or clearance is involved with a variety of eye diseases such as glaucoma and diabetic retinopathy, but measurement of water exchange dynamics in the vitreous and aqueous remain challenging. 2H MRI can be used to image deuterium oxide (D₂O) as a tracer, but the signal-to-noise ratio for deuterium is low due to its low concentration, which has hampered its application to imaging the eye. To overcome this challenge, we investigated the feasibility of direct D2O MRI to measure water dynamics in the mouse eye. The balanced steady-state free precession (bSSFP) sequence provided substantially higher signal-to-noise ratio for imaging D2O in fluid compared to standard gradient echo and spin echo sequences. bSSFP allowed dynamic imaging of intraocular water inflow in the mouse with 41 s temporal resolution. The inflow rate in the vitreous was found to be faster than in the aqueous. These studies demonstrate the feasibility of in vivo imaging of water inflow dynamics into the both the vitreous and aqueous in mice, which could be useful in studies of abnormal fluid exchange in rodent models of eye disease.

The role of conventional and unconventional adaptive routes in lowering of intraocular pressure: Theoretical model and simulation

In this article, we propose a theoretical model leveraging the analogy between fluid and electric variables to investigate the relation among aqueous humor (AH) circulation and drainage and intraocular pressure (IOP), the principal established risk factor of severe neuropathologies of the optic nerve such as glaucoma. IOP is the steady-state result of the balance among AH secretion (AHs), circulation (AHc), and drainage (AHd). AHs are modeled as a given volumetric flow rate electrically corresponding to an input current source. AHc is modeled by the series of two linear hydraulic conductances (HCs) representing the posterior and anterior chambers. AHd is modeled by the parallel of three HCs: a linear HC for the conventional adaptive route (ConvAR), a nonlinear HC for the hydraulic component of the unconventional adaptive route (UncAR), and a nonlinear HC for the drug-dependent component of the UncAR. The proposed model is implemented in a computational virtual laboratory to study the value attained by the IOP under physiological and pathological conditions. Simulation results (i) confirm the conjecture that the UncAR acts as a relief valve under pathological conditions, (ii) indicate that the drug-dependent AR is the major opponent to IOP increase in the case of elevated trabecular meshwork resistance, and (iii) support the use of the model as a quantitative tool to complement in vivo studies and help design and optimize medications for ocular diseases.

Region-related and layer-specific permeability of the iris vasculature with morphological mechanism: A novel understanding of blood-aqueous barrier

The permeability of iris blood vessels has an important role in maintaining aqueous humor (AH) homeostasis, contributing to variation in iris volume and probably the pathogenesis of angle closure glaucoma. This study investigates the permeability of the iris microvasculature to plasma-derived protein and correspond it with the morphologic characteristics of vascular mural cells (MCs). Twenty-two enucleated porcine eyes were used in this study. 12 eyes were micro-perfused with vehicle alone as control or with FITC-albumin as a marker of protein leakage and histological sections subsequently made to examine for FITC-albumin presence. The other 10 eyes were immunolabeled via micro-perfusion for αSMA and VE-cadherin to investigate their topographic distribution in the porcine iris vasculature, and to cross correspond with the locations of FITC-albumin deposits. Distribution of FITC-signals exhibited a site-dependent pattern and time-dependent change in the iris. Fluorescence was initially detected around capillaries in the superficial and deep layer of the iris microvascular network. The pupillary region and the iris root retained more fluorescent signal than the iridal ciliary region. At low magnification, αSMA labelling displayed a regional variation which was inversely correlated with vascular permeability. At the cellular level, αSMA labeling corresponded with vascular MCs distribution in the iris vascular network. The correspondence between iris microvascular permeability to FITC-albumin and the pattern of αSMA distribution and MCs coverage adds to the understanding of the elements comprising the blood-aqueous barrier with implications for the bio-mechanics of iris volume change.

Mechanical Stretch Activates TRPV4 and Hemichannel Responses in the Nonpigmented Ciliary Epithelium

Previously, we reported a mechanosensitive ion channel, TRPV4, along with functional connexin hemichannels on the basolateral surface of the ocular nonpigmented ciliary epithelium (NPE). In the lens, TRPV4-mediated hemichannel opening is part of a feedback loop that senses and respond to swelling. The present study was undertaken to test the hypothesis that TRPV4 and hemichannels in the NPE respond to a mechanical stimulus. Porcine NPE cells were cultured on flexible membranes to study effects of cyclic stretch and ATP release was determined by a luciferase assay. The uptake of propidium iodide (PI) was measured as an indicator of hemichannel opening. NPE cells subjected to cyclic stretch for 1-10 min (10%, 0.5 Hz) displayed a significant increase in ATP release into the bathing medium. In studies where PI was added to the bathing medium, the same stretch stimulus increased cell PI uptake. The ATP release and PI uptake responses to stretch both were prevented by a TRPV4 antagonist, HC067047 (10 µM), and a connexin mimetic peptide, Gap 27 (200µm). In the absence of a stretch stimulus, qualitatively similar ATP release and PI uptake responses were observed in cells exposed to the TRPV4 agonist GSK1016790A (10 nM), and Gap 27 prevented the responses. Cells subjected to an osmotic swelling stimulus (hypoosmotic medium: 200 mOsm) also displayed a significant increase in ATP release and PI uptake and the responses were abolished by TRPV4 inhibition. The findings point to TRPV4-dependent connexin hemichannel opening in response to mechanical stimulus. The TRPV4-hemichannel mechanism may act as a mechanosensor that facilitates the release of ATP and possibly other autocrine or paracrine signaling molecules that influence fluid (aqueous humor) secretion by the NPE.

Noncoding RNAs Are Promising Therapeutic Targets for Diabetic Retinopathy: An Updated Review (2017-2022)

Diabetic retinopathy (DR) is the most common complication of diabetes. It is also the main cause of blindness caused by multicellular damage involving retinal endothelial cells, ganglial cells, and pigment epithelial cells in adults worldwide. Currently available drugs for DR do not meet the clinical needs; thus, new therapeutic targets are warranted. Noncoding RNAs (ncRNAs), a new type of biomarkers, have attracted increased attention in recent years owing to their crucial role in the occurrence and development of DR. NcRNAs mainly include microRNAs, long noncoding RNAs, and circular RNAs, all of which regulate gene and protein expression, as well as multiple biological processes in DR. NcRNAs, can regulate the damage caused by various retinal cells; abnormal changes in the aqueous humor, exosomes, blood, tears, and the formation of new blood vessels. This study reviews the different sources of the three ncRNAs-microRNAs, long noncoding RNAs, and circular RNAs-involved in the pathogenesis of DR and the related drug development progress. Overall, this review improves our understanding of the role of ncRNAs in various retinal cells and offers therapeutic directions and targets for DR treatment.

Ocular manifestations of central insulin resistance

Central insulin resistance, the diminished cellular sensitivity to insulin in the brain, has been implicated in diabetes mellitus, Alzheimer's disease and other neurological disorders. However, whether and how central insulin resistance plays a role in the eye remains unclear. Here, we performed intracerebroventricular injection of S961, a potent and specific blocker of insulin receptor in adult Wistar rats to test if central insulin resistance leads to pathological changes in ocular structures. 80 mg of S961 was stereotaxically injected into the lateral ventricle of the experimental group twice at 7 days apart, whereas buffer solution was injected to the sham control group. Blood samples, intraocular pressure, trabecular meshwork morphology, ciliary body markers, retinal and optic nerve integrity, and whole genome expression patterns were then evaluated. While neither blood glucose nor serum insulin level was significantly altered in the experimental or control group, we found that injection of S961 but not buffer solution significantly increased intraocular pressure at 14 and 24 days after first injection, along with reduced porosity and aquaporin 4 expression in the trabecular meshwork, and increased tumor necrosis factor α and aquaporin 4 expression in the ciliary body. In the retina, cell density and insulin receptor expression decreased in the retinal ganglion cell layer upon S961 injection. Fundus photography revealed peripapillary atrophy with vascular dysregulation in the experimental group. These retinal changes were accompanied by upregulation of pro-inflammatory and pro-apoptotic genes, downregulation of anti-inflammatory, anti-apoptotic, and neurotrophic genes, as well as dysregulation of genes involved in insulin signaling. Optic nerve histology indicated microglial activation and changes in the expression of glial fibrillary acidic protein, tumor necrosis factor α, and aquaporin 4. Molecular pathway architecture of the retina revealed the three most significant pathways involved being inflammation/cell stress, insulin signaling, and extracellular matrix regulation relevant to neurodegeneration. There was also a multimodal crosstalk between insulin signaling derangement and inflammation-related genes. Taken together, our results indicate that blocking insulin receptor signaling in the central nervous system can lead to trabecular meshwork and ciliary body dysfunction, intraocular pressure elevation, as well as inflammation, glial activation, and apoptosis in the retina and optic nerve. Given that central insulin resistance may lead to neurodegenerative phenotype in the visual system, targeting insulin signaling may hold promise for vision disorders involving the retina and optic nerve.

A Mathematical Model of Aqueous Humor Production and Composition

Purpose

We develop a mathematical model that predicts aqueous humor (AH) production rate by the ciliary processes and aqueous composition in the posterior chamber (PC), with the aim of estimating how the aqueous production rate depends on the controlling parameters and how it can be manipulated.

Methods

We propose a compartmental mathematical model that considers the stromal region, ciliary epithelium, and PC. All domains contain an aqueous solution with different chemical species. We impose the concentration of all species on the stromal side and exploit the various ion channels present on the cell membrane to compute the water flux produced by osmosis, the solute concentrations in the AH and the transepithelial potential difference.

Results

With a feasible set of parameters, the model predictions of water flux from the stroma to the PC and of the solute concentrations in the AH are in good agreement with measurements. Key parameters which impact the aqueous production rate are identified. A relevant role is predicted to be played by cell membrane permeability to \(\text{K}^+\) and \(\text{Cl}^-\), by the level of transport due to the Na+-H+ exchanger and to the co-transporter of Na+/K+/2Cl-; and by carbonic anhydrase.

Conclusions

The mathematical model predicts the formation and composition of AH, based on the structure of the ciliary epithelium. The model provides insight into the physical processes underlying the functioning of drugs that are adopted to regulate the aqueous production. It also suggests ion channels and cell membrane properties that may be targeted to manipulate the aqueous production rate.

Changes in Aqueous Humor Lutein Levels of Patients with Cataracts after a 6-Week Course of Lutein-Containing Antioxidant Supplementation

PURPOSE

Oxidative damage is known to be an important cause of age-related cataracts and it has been suggested that administration of antioxidants, such as lutein, may delay the onset and progression of cataracts. Our previous investigation of human aqueous humor after the intake of a lutein-containing supplement demonstrated decreases in peroxidative products. This study evaluated the transportation of lutein into aqueous humor which is an important factor when measuring the antioxidant effects of lutein on the lens.

METHODS

This study enrolled 155 patients with binocular cataracts of the same grade. Serum and aqueous humor samples were collected during cataract surgery before (as pre-intake samples) and after 6 weeks of oral intake of Ocuvite + Lutein^® (as post-intake samples). Lutein levels were measured with high-performance liquid chromatography.

RESULTS

Lutein levels in both the serum and aqueous humor were significantly higher in the post-intake than the pre-intake samples. There were significant increases in the lutein levels in patients with lower pre-intake lutein serum levels. There was also a tendency for greater increases in patients with lower pre-intake aqueous humor lutein levels.

CONCLUSIONS

These results demonstrate that oral lutein supplementation increases lutein levels, which further induce decreases in peroxidation in the aqueous humor. Furthermore, lutein supplementation may be more effective in patients with lower serum lutein levels.

Ocular Autonomic Nervous System: An Update from Anatomy to Physiological Functions

The autonomic nervous system (ANS) confers neural control of the entire body, mainly through the sympathetic and parasympathetic nerves. Several studies have observed that the physiological functions of the eye (pupil size, lens accommodation, ocular circulation, and intraocular pressure regulation) are precisely regulated by the ANS. Almost all parts of the eye have autonomic innervation for the regulation of local homeostasis through synergy and antagonism. With the advent of new research methods, novel anatomical characteristics and numerous physiological processes have been elucidated. Herein, we summarize the anatomical and physiological functions of the ANS in the eye within the context of its intrinsic connections. This review provides novel insights into ocular studies.

Ocular Fluid Mechanics and Drug Delivery: A Review of Mathematical and Computational Models

The human eye is a complex biomechanical structure with a range of biomechanical processes involved in various physiological as well as pathological conditions. Fluid flow inside different domains of the eye is one of the most significant biomechanical processes that tend to perform a wide variety of functions and when combined with other biophysical processes play a crucial role in ocular drug delivery. However, it is quite difficult to comprehend the effect of these processes on drug transport and associated treatment experimentally because of ethical constraints and economic feasibility. Computational modeling on the other hand is an excellent means to understand the associated complexity between these aforementioned processes and drug delivery. A wide range of computational models specific to different types of fluids present in different domains of the eye as well as varying drug delivery modes has been established to understand the fluid flow behavior and drug transport phenomenon in an insilico manner. These computational models have been used as a non-invasive tool to aid ophthalmologists in identifying the challenges associated with a particular drug delivery mode while treating particular eye diseases and to advance the understanding of the biomechanical behavior of the eye. In this regard, the author attempts to summarize the existing computational and mathematical approaches proposed in the last two decades for understanding the fluid mechanics and drug transport associated with different domains of the eye, together with their application to modify the existing treatment processes.

Anterior pituitary, sex hormones, and keratoconus: Beyond traditional targets

"The Diseases of the Horny-coat of The Eye", known today as keratoconus, is a progressive, multifactorial, non-inflammatory ectatic corneal disorder that is characterized by steepening (bulging) and thinning of the cornea, irregular astigmatism, myopia, and scarring that can cause devastating vision loss. The significant socioeconomic impact of the disease is immeasurable, as patients with keratoconus can have difficulties securing certain jobs or even joining the military. Despite the introduction of corneal crosslinking and improvements in scleral contact lens designs, corneal transplants remain the main surgical intervention for treating keratoconus refractory to medical therapy and visual rehabilitation. To-date, the etiology and pathogenesis of keratoconus remains unclear. Research studies have increased exponentially over the years, highlighting the clinical significance and international interest in this disease. Hormonal imbalances have been linked to keratoconus, both clinically and experimentally, with both sexes affected. However, it is unclear how (molecular/cellular signaling) or when (age/disease stage(s)) those hormones affect the keratoconic cornea. Previous studies have categorized the human cornea as an extragonadal tissue, showing modulation of the gonadotropins, specifically luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Studies herein provide new data (both in vitro and in vivo) to further delineate the role of hormones/gonadotropins in the keratoconus pathobiology, and propose the existence of a new axis named the Hypothalamic-Pituitary-Adrenal-Corneal (HPAC) axis.

Effect of Topical Phenylephrine 2.5% on Episcleral Venous Pressure in Normal Human Eyes

Purpose

Phenylephrine has been shown to affect intraocular pressure (IOP) but the mechanism of action is poorly understood. However, its action as a vasoconstrictor suggests possible effects on episcleral venous pressure (EVP). In this study, we evaluated the effect of phenylephrine on EVP and IOP in healthy subjects.

Methods

Forty eyes of 20 subjects were included. Each subject received 3 drops of phenylephrine 2.5% in one eye at 1-minute intervals. The fellow eye served as control. Blood pressure, heart rate, and IOP and EVP of both eyes were measured at baseline, 15 minutes, and 60 minutes after instillation of phenylephrine. IOP was measured by pneumatonometry. EVP was assessed by using a computer-controlled episcleral venomanometer. Changes in IOP, EVP, blood pressure, and heart rate at 15 and 60 minutes were analyzed by paired t-tests.

Results

IOP increased 15 minutes after instillation of phenylephrine in both treated (P = 0.001) and control eyes (P = 0.01) and returned to baseline at 60 minutes. The change in IOP at 15 minutes was not significantly different between the 2 groups. EVP in treated eyes was unchanged at 15 minutes (P = 0.8) but decreased significantly at 60 minutes (P < 0.001). In control eyes, there was no change in EVP at any time (P > 0.6). There were no significant changes from baseline in systolic and diastolic blood pressure and heart rate after instillation of phenylephrine.

Conclusions

IOP elevation associated with topical phenylephrine is not caused by an increase in EVP in healthy subjects. Instead, EVP decreases with phenylephrine, but the mechanism remains to be determined.

Glucose levels between the anterior chamber of the eye and blood are correlated based on blood glucose dynamics

Glycemic control is essential to manage metabolic diseases such as diabetes. Frequent measurements of systemic glucose levels with prompt managements can prevent organ damages. The eye is a glucose highly demanding organ in our body, and the anterior chamber (AC) in the eye has been suggested for a noninvasive blood glucose monitoring site. However, calculating blood glucose levels from measuring glucose levels in AC has been difficult and unclear. In this study, we aimed to examine glucose levels from AC and find a correlation with blood glucose levels. A total of 30 patients with cataracts (men and women, study 1; 7 and 3, study 2; 9 and 11) who visited Keio University Hospital from 2015 to 2018 and agreed to participate in this study were recruited. Glucose levels from AC and the blood were examined by a UV-hexokinase or H2O2-electrode method before/during the cataract surgery. These values were analyzed with regression analyses depending on the groups (blood glucose-ascending and descending groups). In the blood glucose-descending group, glucose levels from AC were strongly correlated with blood glucose levels (a high R2 value, 0.8636). However, the relatively moderate correlation was seen in the blood glucose-ascending group (a low R2 value, 0.5228). Taken together, we showed different correlation ratios on glucose levels between AC and the blood, based on blood glucose dynamics. Stacking data regarding this issue would enable establishing noninvasive blood glucose monitoring from measuring glucose levels in AC more correctly, which will be helpful for proper and prompt managements for glucose-mediated complications.

Mechanistic links between systemic hypertension and open angle glaucoma

Systemic hypertension or hypertension is a very common chronic age-related disease worldwide. It is typically characterised by a sustained elevation of blood pressure, particularly when the systolic blood pressure and/or diastolic blood pressure are of more than 140 mmHg and 90 mmHg, respectively. If hypertension is not well controlled, it may lead to an increased risk of stroke and heart attack. It has been shown that hypertension is linked to various ocular diseases, including cataract, diabetic retinopathy, age-related macular degeneration, and glaucoma. Glaucoma is the leading cause of irreversible blindness worldwide. Primary open angle glaucoma is the most common form of the disease and is usually characterised by an increase in intraocular pressure. This condition, together with normal tension glaucoma, constitutes open angle glaucoma. Systemic hypertension has been identified as a risk factor for open angle glaucoma. It is speculated that blood pressure is involved in the pathogenesis of open angle glaucoma by altering intraocular pressure or ocular blood flow, or both. Recent evidence has shown that both extremely high and low blood pressure are associated with increased risk of open angle glaucoma. Additional pathogenic mechanisms, including increased inflammation likely to be involved in the development and progression of these two diseases, are discussed.

The role of peroxisome proliferator-activated receptors in healthy and diseased eyes

Peroxisome Proliferator-Activated Receptors (PPARs) are a family of nuclear receptors that play essential roles in modulating cell differentiation, inflammation, and metabolism. Three subtypes of PPARs are known: PPAR-alpha (PPARα), PPAR-gamma (PPARγ), and PPAR-beta/delta (PPARβ/δ). PPARα activation reduces lipid levels and regulates energy homeostasis, activation of PPARγ results in regulation of adipogenesis, and PPARβ/δ activation increases fatty acid metabolism and lipolysis. PPARs are linked to various diseases, including but not limited to diabetes, non-alcoholic fatty liver disease, glaucoma and atherosclerosis. In the past decade, numerous studies have assessed the functional properties of PPARs in the eye and key PPAR mechanisms have been discovered, particularly regarding the retina and cornea. PPARγ and PPARα are well established in their functions in ocular homeostasis regarding neuroprotection, neovascularization, and inflammation, whereas PPARβ/δ isoform function remains understudied. Naturally, studies on PPAR agonists and antagonists, associated with ocular pathology, have also gained traction with the development of PPAR synthetic ligands. Studies on PPARs has significantly influenced novel therapeutics for diabetic eye disease, ocular neuropathy, dry eye, and age-related macular degeneration (AMD). In this review, therapeutic potentials and implications will be highlighted, as well as reported adverse effects. Further investigations are necessary before any of the PPARs ligands can be utilized, in the clinics, to treat eye diseases. Future research on the prominent role of PPARs will help unravel the complex mechanisms involved in order to prevent and treat ocular diseases.

Lymphatics in Eye Fluid Homeostasis: Minor Contributors or Significant Actors?

Lymphatic vessels exert major effects on the maintenance of interstitial fluid homeostasis, immune cell trafficking, lipid absorption, tumor progression and metastasis. Recently, novel functional roles for the lymphatic vasculature have emerged, which can be associated with pathological situations. Among them, lymphatics have been proposed to participate in eye aqueous humor drainage, with potential consequences on intraocular pressure, a main risk factor for progression of glaucoma disease. In this review, after the description of eye fluid dynamics, we provide an update on the data concerning the distribution of ocular lymphatics. Particular attention is given to the results of investigations allowing the three dimensional visualization of the ocular surface vasculature, and to the molecular mechanisms that have been characterized to regulate ocular lymphatic vessel development. The studies concerning the potential role of lymphatics in aqueous humor outflow are reported and discussed. We also considered the novel studies mentioning the existence of an ocular glymphatic system which may have, in connection with lymphatics, important repercussions in retinal clearance and in diseases affecting the eye posterior segment. Some remaining unsolved questions and new directions to explore are proposed to improve the knowledge about both lymphatic and glymphatic system interactions with eye fluid homeostasis.

The Association of Intraocular Pressure With Obesity and Cardiometabolic Risk in a Young Farmworker Population

PRCIS

Intraocular pressure (IOP) was found to be significantly correlated with body mass index (BMI), waist circumference, and diastolic blood pressure (DBP) in a farmworker population located in the southeast Georgia, USA. BMI was correlated with IOP, independent of systemic blood pressures.

PURPOSE

Elevated IOP is a known risk factor for glaucomatous optic neuropathy and is believed to be associated with obesity and cardiometabolic diseases. The high prevalence of these conditions in the United States necessitates an evaluation of the relationship among obesity, cardiometabolic risks, and IOP among understudied younger populations.

MATERIALS AND METHODS

Farmworker data were collected from the annual Costa-Layman Health Fair between 2013 and 2017. Correlations of IOP with demographic factors, obesity, and cardiometabolic risks were analyzed using analysis of covariance, partial Pearson correlations, and linear regressions.

RESULTS

In the farmworker population (n=346), the mean IOP was 15.5 mm Hg and the prevalence of ocular hypertension (IOP>21 mm Hg) was 5.5%. BMI, waist circumference, and DBP were significantly correlated (r=0.192, P=0.001; r=0.128, P=0.017; r=0.142, P=0.007, respectively) with IOP when adjusted for age, sex, and ethnicity. Each 10 mm Hg increase in DBP corresponded with a 0.51 mm Hg increase in IOP. With adjustment for age, sex, ethnicity, systolic blood pressure, and DBP, BMI remained significantly correlated with IOP (r=0.166, P=0.002).

CONCLUSIONS

Higher IOP is associated with obesity measures including BMI and waist circumference and is correlated with DBP. These findings suggest that BMI is an independent risk factor for elevated IOP.

Attenuation of the increase in intraocular pressure with dexmedetomidine: Systematic review with meta-analysis and trial sequential analysis

STUDY OBJECTIVE

Whether dexmedetomidine effectively attenuates the increase in intraocular pressure (IOP) remains inconclusive. We aim to evaluate the effects of dexmedetomidine on IOP in adult patients undergoing surgery which requires general anesthesia and endotracheal intubation.

DESIGN

Systematic review and meta-analysis.

INTERVENTIONS

Intravenous administration of dexmedetomidine during surgery.

MEASUREMENTS

Intraocular pressure.

METHODS

We searched PubMed, Embase, Scopus, Web of Science, Cochrane Library, Google Scholar, Wanfang Data, and China National Knowledge Infrastructure from the inception through April 14, 2020. Randomized control trials which involved adult patients undergoing surgery that required general anesthesia and endotracheal intubation, which compared intravenous administration of dexmedetomidine with placebo regarding the IOP levels, which also provided sufficient information for meta-analysis were considered eligible.

MAIN RESULTS

Twenty-nine randomized control trials were included. The IOP levels are significantly lower in patients receiving dexmedetomidine after the administration of dexmedetomidine [mean difference (MD), -2.04 mmHg; 95% confidence interval (CI), -2.40 mmHg to -1.67 mmHg], after the injection of succinylcholine (MD, -3.84 mmHg; 95% CI, -4.80 mmHg to -2.88 mmHg), after endotracheal intubation (MD, -3.64 mmHg; 95% CI, -4.46 mmHg to -2.82 mmHg), after pneumoperitoneum (MD, -3.12 mmHg; 95% CI, -3.93 mmHg to -2.30 mmHg), and after the patients being placed in a steep Trendelenburg position (MD, -4.12 mmHg; 95% CI, -5.39 mmHg to -2.85 mmHg). Trial sequential analyses for these outcomes are conclusive.

CONCLUSIONS

Dexmedetomidine effectively attenuates the increase in IOP levels, and should be considered especially for at-risk patients.

Insights into the regulatory molecules involved in glaucoma pathogenesis

Glaucoma is an important cause of irreversible blindness, characterized by optic nerve anomalies. Increased intraocular pressure (IOP) and aging are major risk factors. Retinal ganglion cells and trabecular meshwork cells are certainly involved in the etiology of glaucoma. Glaucoma is usually a complex disease, and various genes and functions may contribute to its etiology. Among these may be genes that encode regulatory molecules. In this review, regulatory molecules including 18 transcription factors (TFs), 195 microRNAs (miRNAs), 106 long noncoding RNAs (lncRNAs), and two circular RNAs (circRNAs) that are reasonable candidates for having roles in glaucoma pathogenesis are described. The targets of the regulators are reported. Glaucoma-related features including apoptosis, stress responses, immune functions, ECM properties, IOP, and eye development are affected by the targeted genes. The targeted genes that are frequently targeted by multiple regulators most often affect apoptosis and the related features of cell death and cell survival. BCL2, CDKN1A, and TP53 are among the frequent targets of three types of glaucoma-relevant regulators, TFs, miRNAs, and lncRNAs. TP53 was itself identified as a glaucoma-relevant TF. Several of the glaucoma-relevant TFs are themselves among frequent targets of regulatory molecules, which is consistent with existence of a complex network involved in glaucoma pathogenesis.

Intraocular Pressure Responses to Four Different Isometric Exercises in Men and Women

SIGNIFICANCE

The performance of resistance exercise has evidenced to induce abrupt intraocular pressure (IOP) changes, which has been linked to the onset and progression of glaucoma. We found that four different isometric resistance exercises lead to an instantaneous and progressive IOP elevation, with these changes being independent of the type of exercise.

PURPOSE

The impact of physical exercise on IOP has demonstrated to be dependent on exercise type and intesity, as well as individuals' characteristics. In this study, we aimed to explore the influence of the load, exercise type, and participant's sex on the IOP behavior during a 2-minute isometric effort.

METHODS

Twenty-eight physically active collegiate students performed 2 minutes of isometric exercise in the military press, biceps curl, leg extension, and calf raise exercises against two different loads (high load and low load). Intraocular pressure was measured by rebound tonometry before, during (semicontinuos assessment [24 measurements]), and after 10 seconds of recovery in each of the eight (four exercises × two loads) conditions.

RESULTS

We found a statistically significant effect of load (P < .001, np = 0.906), with greater IOP values when performing the isometric exercises against heavier loads. There was a positive IOP rise during the execution of isometric exercise in the high-load condition, returning to baseline levels after 10 seconds of passive recovery. The exercise type and participant's sex did not reveal statistically significant differences (P = .33 and P = .56, respectively).

CONCLUSIONS

Our data evidenced an instanteneous and progressive IOP rise during the execution of isometric exercise leading to muscular failure, regardless of the exercise type and participant's sex. After exercise, IOP rapidly retuned to baseline levels (within 10 seconds). The inclusion of glaucoma patients in future studies is guarranteed.

The Mont Blanc Study: The effect of altitude on intra ocular pressure and central corneal thickness

The aim of the Mont Blanc Study was to investigate the relationship between intraocular pressure (IOP), central corneal thickness (CCT), and altitude in healthy subjects. Thirty-three eyes of 33 healthy volunteers (mean age: 24.8 years, 17 females) had their IOP measured with Perkins and I-Care tonometers and their CCT using ultrasound pachymetry at three locations in Italy with different altitudes: Pavia, (PV), 77 meters above sea level (a.s.l); Courmayeur (CM), 1300 meters a.s.l; Pointe Helbronner (PH), 3466 meters a.s.l.). The measurements were performed at 9 am, 11 am, 1 pm and 3 pm (±30’) in indoor settings (mean temperature of 19°C) in PV and PH. At 9 am, CCT and IOP were measured outdoor (mean temperature of -1.4°C) at PH. The mean values of the IOP curve decreased from PV to PH with the Perkins (p = 0.02) and I-Care tonometers (p = 0.001). Instead, CCT increased upon ascension from PV to PH (p = 0.01), and from CM to PH (p = 0.002). When exposed to sub-zero temperature, the IOP increased (p<0.001), while the CCT did not change (p = 0.30). The results suggest that IOP significantly decreased and CCT significantly increased upon ascension from the sea level to higher altitudes.

A Theoretical Approach for the Electrochemical Characterization of Ciliary Epithelium

The ciliary epithelium (CE) is the primary site of aqueous humor (AH) production, which results from the combined action of ultrafiltration and ionic secretion. Modulation of ionic secretion is a fundamental target for drug therapy in glaucoma, and therefore it is important to identify the main factors contributing to it. As several ion transporters have been hypothesized as relevant players in CE physiology, we propose a theoretical approach to complement experimental methods in characterizing their role in the electrochemical and fluid-dynamical conditions of CE. As a first step, we compare two model configurations that differ by (i) types of transporters included for ion exchange across the epithelial membrane, and by (i) presence or absence of the intracellular production of carbonic acid mediated by the carbonic anhydrase enzyme. The proposed model configurations do not include neurohumoral mechanisms such as P2Y receptor-dependent, cAMP, or calcium-dependent pathways, which occur in the ciliary epithelium bilayer and influence the activity of ion transporters, pumps, and channels present in the cell membrane. Results suggest that one of the two configurations predicts sodium and potassium intracellular concentrations and transmembrane potential much more accurately than the other. Because of its quantitative prediction power, the proposed theoretical approach may help relate phenomena at the cellular scale, that cannot be accessed clinically, with phenomena occurring at the scale of the whole eye, for which clinical assessment is feasible.

Association Between Arterial Blood Gas Variation and Intraocular Pressure in Healthy Subjects Exposed to Acute Short-Term Hypobaric Hypoxia

Purpose

To investigate the association between changes in arterial blood gases and intraocular pressure (IOP) after acute, short-term exposure to simulated elevation of 4000 m above sea level.

Methods

Twenty-five healthy young lowlanders participated in this prospective study. IOP was measured in both eyes with an Accupen tonometer. Arterial blood gas parameters (partial oxygen pressure [PaO₂], partial carbon dioxide pressure [PaCO₂], pH, and bicarbonate ion [HCO₃ ^-]) were checked using a blood gas analyzer. Measurements were taken at sea level (T1), at 15-minute (T2) and at 2-hour (T3) exposure times to simulated 4000 m above sea level in a hypobaric chamber, and upon return to sea level (T4). Associations between arterial blood gas parameters and IOP were evaluated using multivariate linear regression.

Results

PaO₂ significantly decreased at T2 and T3, resolving at T4 (P < 0.001). pH significantly increased at T2 and returned to baseline at T3 (P = 0.004). Actual and standard bicarbonate ion both dropped with IOP at T3 and T4. IOP significantly decreased from 16.4 ± 3.4 mm Hg at T1 to 15.1 ± 2.1 mm Hg (P = 0.041) at T3 and remained lower (14.9 ± 2.4 mm Hg; P = 0.029) at T4. IOP was not correlated with pH. Multivariate linear regression showed that lower IOP was associated with lower standard bicarbonate ion (beta = -1.061; 95% confidence interval, -0.049 to -2.074; P = 0.04) when adjusted for actual bicarbonate and diastolic blood pressure.

Conclusions

Hypobaric hypoxia triggers plasma bicarbonate ion reduction which, rather than pH, may decrease aqueous humor formation and subsequently cause IOP reduction. These findings may shed light on the mechanism of IOP regulation at high altitude.

Translational Relevance

Hypoxia-triggered reduction in plasma bicarbonate ion may decrease aqueous humor production, leading to IOP reduction at high altitude. These findings may provide new insight into a potential mechanism of IOP regulation. Hypobaric hypoxia at high altitude is an environmental factor that can reduce IOP and, therefore, deserves further study.

Identification of genes involved in glaucoma pathogenesis using combined network analysis and empirical studies

Glaucoma is a leading cause of blindness. We aimed in this study to identify genes that may make subtle and cumulative contributions to glaucoma pathogenesis. To this end, we identified molecular interactions and pathways that include transcription factors (TFs) FOXC1, PITX2, PAX6 and NFKB1 and various microRNAs including miR-204 known to have relevance to trabecular meshwork (TM) functions and/or glaucoma. TM tissue is involved in glaucoma pathogenesis. In-house microarray transcriptome results and data sources were used to identify target genes of the regulatory molecules. Bioinformatics analyses were done to filter TM and glaucoma relevant genes. These were submitted to network-creating softwares to define interactions, pathways and a network that would include the genes. The network was stringently scrutinized and minimized, then expanded by addition of microarray data and data on TF and microRNA-binding sites. Selected features of the network were confirmed by empirical studies such as dual luciferase assays, real-time PCR and western blot experiments and apoptosis assays. MYOC, WDR36, LTPBP2, RHOA, CYP1B1, OPA1, SPARC, MEIS2, PLEKHG5, RGS5, BBS5, ALDH1A1, NOMO2, CXCL6, FMNL2, ADAMTS5, CLOCK and DKK1 were among the genes included in the final network. Pathways identified included those that affect ECM properties, IOP, ciliary body functions, retinal ganglion cell viability, apoptosis, focal adhesion and oxidative stress response. The identification of many genes potentially involved in glaucoma pathology is consistent with its being a complex disease. The inclusion of several known glaucoma-related genes validates the approach used.

Longitudinal observation of intraocular pressure variations with acute altitude changes

BACKGROUND

Higher intraocular pressure (IOP) is a major risk factor for developing glaucoma, and the leading cause of irreversible blindness worldwide. High altitude (HA) may be involved in IOP, but the reported results were conflicting. Ascent to HA directly by plane from low altitude regions is an acute, effortless exposure. However, the effects of such exposure to different altitudes on IOP have rarely been reported.

AIM

To investigate changes in IOP after rapid effortless exposure to HA in stages and compare it with systemic parameters.

METHODS

Fifty-eight healthy subjects (116 eyes) were divided into three groups: 17 low-altitude (LA) residents [44 m above sea level (ASL)], 22 HA residents (2261 m ASL) and 19 very HA (VHA) residents (3750 m ASL). The LA group flew to HA first. Three days later, they flew with the HA group to VHA where both groups stayed for 2 d. Then, the LA group flew back to HA and stayed for 1 d before flying back to 44 m. IOP, oxygen saturation (SpO₂) and pulse rate were measured. The linear mixed model was used to compare repeated measurements.

RESULTS

IOP in the LA group significantly decreased from 18.41 ± 2.40 mmHg at 44 m to 13.60 ± 3.68 mmHg at 2261 m ASL (P < 0.001), and then to 11.85 ± 2.48 mmHg at 3750 m ASL (P = 0.036 compared to IOP at 2261 m ASL) and partially recovered to 13.47 ± 2.57 mmHg upon return to 44 m. IOP in the LA group at HA and VHA was comparable to that in the local residents (12.2 ± 2.4 mmHg for HA,11.5 ± 1.8 mmHg for VHA). IOP was positively associated with SpO₂ while negatively associated with pulse rate.

CONCLUSION

IOP in the LA group gradually reduced as altitude elevated in stages and became comparable to IOP in local residents. Hypoxia may be associated with IOP, which deserves further study.

Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions

This work aims at investigating the interactions between the flow of fluids in the eyes and the brain and their potential implications in structural and functional changes in the eyes of astronauts, a condition also known as spaceflight associated neuro-ocular syndrome (SANS). To this end, we propose a reduced (0-dimensional) mathematical model of fluid flow in the eyes and brain, which is embedded into a simplified whole-body circulation model. In particular, the model accounts for: (i) the flows of blood and aqueous humor in the eyes; (ii) the flows of blood, cerebrospinal fluid and interstitial fluid in the brain; and (iii) their interactions. The model is used to simulate variations in intraocular pressure, intracranial pressure and blood flow due to microgravity conditions, which are thought to be critical factors in SANS. Specifically, the model predicts that both intracranial and intraocular pressures increase in microgravity, even though their respective trends may be different. In such conditions, ocular blood flow is predicted to decrease in the choroid and ciliary body circulations, whereas retinal circulation is found to be less susceptible to microgravity-induced alterations, owing to a purely mechanical component in perfusion control associated with the venous segments. These findings indicate that the particular anatomical architecture of venous drainage in the retina may be one of the reasons why most of the SANS alterations are not observed in the retina but, rather, in other vascular beds, particularly the choroid. Thus, clinical assessment of ocular venous function may be considered as a determinant SANS factor, for which astronauts could be screened on earth and in-flight.

Relationship Between the Parameters of Corneal and Fundus Pulse Signals Acquired With a Combined Ultrasound and Laser Interferometry Technique

Purpose

To estimate the relationship between the characteristics of the corneal pulse (CP) signal and those of the fundus pulse (FP) signal measured with a combined noncontact ultrasonic and laser interferometry technique in healthy subjects.

Methods

Twenty-two healthy subjects participated in experiments that included measurements of intraocular pressure, ocular pulse amplitude, ocular biometry, blood pressure, and heart rate. Additionally, simultaneous recordings of CP and FP signals were acquired with a noncontact ultrasonic device combined with laser interferometry. Subsequently, ocular perfusion pressure (OPP) and the time and spectral parameters of CP and FP signals were computed. A system model was proposed to relate the FP signal to the CP signal.

Results

The system model revealed that the eye globe transfers information between signals of the posterior and anterior eye, relatively amplifying higher spectral harmonics. The amplitude of the second CP harmonic is predicted by FP_RMS and OPP (R² = 0.468, P = 0.002). Partial correlation analysis showed that the CP signal parameters are statistically significantly correlated with those of the FP signal and OPP, after correcting for age and sex.

Conclusions

The eye globe can be viewed as a high pass filter, in which the CP characteristic changes in relation to the fundus pulsation. The FP signal and OPP have an impact on the variations of the CP signal morphology.

Translational Relevance

Investigation of differences between the characteristics of the anterior and posterior tissue movements is a promising method for evaluating the role of circulatory and biomechanical components in the pathophysiology of ocular diseases.

Ocular hypotony: A comprehensive review

Ocular hypotony is an infrequent, yet potentially vision-threatening, entity. The list of differential causes is extensive, involving any condition that may compromise aqueous humor dynamics or the integrity of the globe and sometimes following medical treatments or procedures. Depending on the cause and the clinical impact, treatment options aim to correct the underlying pathology and to reestablish anatomical integrity, as well as visual function. We review the pathophysiology, clinical presentation, different causes, and associated therapeutic options of ocular hypotony.

Inter-relationship between ageing, body mass index, diabetes, systemic blood pressure and intraocular pressure in Asians: 6-year longitudinal study

BACKGROUND

To investigate the biological effect of ageing on intraocular pressure (IOP) and risk factors in a population-based cohort study of Malay and Indian adults.

METHODS

Participants aged 40-80 years were recruited for baseline and 6-year follow-up visits between 2004-2009 and 2010-2015, respectively. Blood pressure (BP) was measured with an automatic BP monitor and IOP were obtained by Goldmann applanation tonometry. Main outcome was change in IOP, defined as the difference between the 6-year IOP and the baseline IOP. Linear regression models were used to investigate the association of changes in IOP with risk factors.

RESULTS

Participants without a history of glaucoma or cataract surgery at baseline were included (n = 3188; mean age: 54±9 years) . Their average IOP was reduced (-0.5±3.1 mm Hg), except for those who developed hypertension at follow-up (0.0±3.1 mm Hg). After adjusting for covariates, changes in IOP were negatively associated with age (β=-0.07, 95% CI -0.13 to -0.01) and positively associated with body mass index, diabetes, hypertension (normotensive as reference group; newly developed hypertensive (β=0.67, 95% CI 0.39 to 0.95) and chronic hypertensive (β=0.46, 95% CI 0.22 to 0.70)), baseline systolic BP (SBP) (β=0.20, 95% CI 0.14 to 0.26) and diastolic BP (DBP) (β=0.33, 95% CI 0.22 to 0.44), as well as with 6-year increases in SBP (β=0.27, 95% CI 0.21 to 0.33) and DBP (β=0.52, 95% CI 0.41 to 0.63).

CONCLUSIONS

Normal ageing and reduced systemic BP are associated with reduced IOP in Malay and Indian adults. Given that high IOP is a risk factor for glaucoma, our finding highlights the importance of controlling hypertension in older adults, where hypertension and glaucoma incidences are on a rise.

A common humoral background of intraocular and arterial blood pressure dysregulation

BACKGROUND

It has been postulated that intraocular pressure, an important glaucoma risk factor, correlates positively with arterial blood pressure (blood pressure). However, results of experimental and clinical studies are often contradictory. It is hypothesized that, in some hypertensive patients, disturbances in intraocular pressure regulation may depend on biological effects of blood borne hormones underlying a particular type of hypertension, rather than on blood pressure level itself.

REVIEW

This review compares the effects of hormones on blood pressure and intraocular pressure, in order to identify a hormonal profile of hypertensive patients with an increased risk of intraocular pressure surge. The PUBMED database was searched to identify pre-clinical and clinical studies investigating the role of angiotensin II, vasopressin, adrenaline, noradrenaline, prostaglandins, and gaseous transmitters in the regulation of blood pressure and intraocular pressure.

RESULTS

Studies included in the review suggest that intraocular and blood pressures often follow a different pattern of response to the same hormone. For example, vasopressin increases blood pressure, but decreases intraocular pressure. In contrast, high level of nitric oxide decreases blood pressure, but increases intraocular pressure.

CONCLUSIONS

Arterial hypertension is associated with altered levels of blood borne hormones. Contradicting results of studies on the relationship between arterial hypertension and intraocular pressure might be partially explained by diverse effects of hormones on arterial and intraocular pressures. Further studies are needed to evaluate if hormonal profiling may help to identify glaucoma-prone patients.

Estimating outflow facility through pressure dependent pathways of the human eye

We develop and test a new theory for pressure dependent outflow from the eye. The theory comprises three main parameters: (i) a constant hydraulic conductivity, (ii) an exponential decay constant and (iii) a no-flow intraocular pressure, from which the total pressure dependent outflow, average outflow facilities and local outflow facilities for the whole eye may be evaluated. We use a new notation to specify precisely the meaning of model parameters and so model outputs. Drawing on a range of published data, we apply the theory to animal eyes, enucleated eyes and in vivo human eyes, and demonstrate how to evaluate model parameters. It is shown that the theory can fit high quality experimental data remarkably well. The new theory predicts that outflow facilities and total pressure dependent outflow for the whole eye are more than twice as large as estimates based on the Goldman equation and fluorometric analysis of anterior aqueous outflow. It appears likely that this discrepancy can be largely explained by pseudofacility and aqueous flow through the retinal pigmented epithelium, while any residual discrepancy may be due to pathological processes in aged eyes. The model predicts that if the hydraulic conductivity is too small, or the exponential decay constant is too large, then intraocular eye pressure may become unstable when subjected to normal circadian changes in aqueous production. The model also predicts relationships between variables that may be helpful when planning future experiments, and the model generates many novel testable hypotheses. With additional research, the analysis described here may find application in the differential diagnosis, prognosis and monitoring of glaucoma.

Making Basic Science Studies in Glaucoma More Clinically Relevant: The Need for a Consensus

Glaucoma is a chronic, progressive, and debilitating optic neuropathy that causes retinal damage and visual defects. The pathophysiologic mechanisms of glaucoma remain ill-defined, and there is an indisputable need for contributions from basic science researchers in defining pathways for translational research. However, glaucoma researchers today face significant challenges due to the lack of a map of integrated pathways from bench to bedside and the lack of consensus statements to guide in choosing the right research questions, techniques, and model systems. Here, we present the case for the development of such maps and consensus statements, which are critical for faster development of the most efficacious glaucoma therapy. We underscore that interrogating the preclinical path of both successful and unsuccessful clinical programs is essential to defining future research. One aspect of this is evaluation of available preclinical research tools. To begin this process, we highlight the utility of currently available animal models for glaucoma and emphasize that there is a particular need for models of glaucoma with normal intraocular pressure. In addition, we outline a series of discoveries from cell-based, animal, and translational research that begin to reveal a map of glaucoma from cell biology to physiology to disease pathology. Completion of these maps requires input and consensus from the global glaucoma research community. This article sets the stage by outlining various approaches to such a consensus. Together, these efforts will help accelerate basic science research, leading to discoveries with significant clinical impact for people with glaucoma.

The impact of ocular hemodynamics and intracranial pressure on intraocular pressure during acute gravitational changes

Exposure to microgravity causes a bulk fluid shift toward the head, with concomitant changes in blood volume/pressure, and intraocular pressure (IOP). These and other factors, such as intracranial pressure (ICP) changes, are suspected to be involved in the degradation of visual function and ocular anatomical changes exhibited by some astronauts. This is a significant health concern. Here, we describe a lumped-parameter numerical model to simulate volume/pressure alterations in the eye during gravitational changes. The model includes the effects of blood and aqueous humor dynamics, ICP, and IOP-dependent ocular compliance. It is formulated as a series of coupled differential equations and was validated against four existing data sets on parabolic flight, body inversion, and head-down tilt (HDT). The model accurately predicted acute IOP changes in parabolic flight and HDT, and was satisfactory for the more extreme case of inversion. The short-term response to the changing gravitational field was dominated by ocular blood pressures and compliance, while longer-term responses were more dependent on aqueous humor dynamics. ICP had a negligible effect on acute IOP changes. This relatively simple numerical model shows promising predictive capability. To extend the model to more chronic conditions, additional data on longer-term autoregulation of blood and aqueous humor dynamics are needed.NEW & NOTEWORTHY A significant percentage of astronauts present anatomical changes in the posterior eye tissues after spaceflight. Hypothesized increases in ocular blood volume and intracranial pressure (ICP) in space have been considered to be likely factors. In this work, we provide a novel numerical model of the eye that incorporates ocular hemodynamics, gravitational forces, and ICP changes. We find that changes in ocular hemodynamics govern the response of intraocular pressure during acute gravitational change.

Changes in Surface Tension of Aqueous Humor in Anterior Segment Ocular Pathologies

The aim of this study was to identify and determine differences in surface tension (ST) of aqueous humor (AH) in patients with cataract, glaucoma and Fuchs endothelial dystrophy (FED). Two hundred and two samples of AH were analyzed (control n = 22; cataract n = 56; glaucoma n = 81; and n = FED 43). Patients with previous history of anterior segment surgery, anterior segment pathology or intraocular injections were excluded from the study. Different types of glaucoma were identified, cataracts were graded using total phaco time data during surgery and clinical severity of FED was assessed by clinical examination. Around 150 microliters AH were obtained during the first step of a surgical procedure, lensectomy, phacoemulsification, nonpenetrating deep sclerotomy (NPDE) and Descemet membrane endothelial keratoplasty (DMEK). A pendant drop-based optical goniometer OCA-15 (Dataphysics, Filderstadt, Germany) was used to measure surface tension. Mean ST was 65.74 ± 3.76 mN/m, 63.59 ± 5.50 mN/m, 64.35 ± 6.99 mN/m, and 60.89 ± 3.73 mN/m in control, cataract, glaucoma and FED patients respectively. Statistically significant differences between FED and control group were found (p < 0.001). Lens condition, cataract maturity, age, and gender did not show influence in ST. ST of AH is significantly decreased in FED patients independently from age and lens condition. These findings may aid to the understanding of the physiopathology of the disease.

Intraocular pressure and ocular biometric parameters changes in migraine

Background

The aim of this study was to assess the intraocular pressure and ocular biometric parameters in migraine patients during acute migraine attacks and compare them with painless period and healthy controls using a new optical biometer AL-Scan.

Methods

In this prospective, case–control study, the axial length, corneal curvature radius, anterior chamber depth, central corneal thickness, and pupil size of 40 migraine patients during acute migraine attacks and painless period and 40 age- and sex-matched healthy subjects were measured using a AL-Scan optical biometer (Nidek Co., Gamagori, Japan). All patients underwent a complete ophthalmic examination before the measurements. IOP and biometer measurements were taken at the same time of day (10:00–12:00) in order to minimize the effects of diurnal variation.

Results

There was not a statistically significant difference in intraocular pressure between the migraine patients during acute migraine attacks (15.07 mmHg), painless period (14.10 mmHg), and the controls (15,73 ± 0,81). Also, the ocular biometric parameters did not significantly vary during the acute migraine attacks.

Conclusions

Further studies are needed to evaluate the etiopathologic relationship between intraocular pressure and ocular biometric parameters and acute migraine attack.

The exit strategy: Pharmacological modulation of extracellular matrix production and deposition for better aqueous humor drainage

Primary open angle glaucoma (POAG) is an optic neuropathy and an irreversible blinding disease. The etiology of glaucoma is not known but numerous risk factors are associated with this disease including aging, elevated intraocular pressure (IOP), race, myopia, family history and use of steroids. In POAG, the resistance to the aqueous humor drainage is increased leading to elevated IOP. Lowering the resistance and ultimately the IOP has been the only way to slow disease progression and prevent vision loss. The primary drainage pathway comprising of the trabecular meshwork (TM) is made up of relatively large porous beams surrounded by extracellular matrix (ECM). Its juxtacanalicular tissue (JCT) or the cribriform meshwork is made up of cells embedded in dense ECM. The JCT is considered to offer the major resistance to the aqueous humor outflow. This layer is adjacent to the endothelial cells forming Schlemm's canal, which provides approximately 10% of the outflow resistance. The ECM in the TM and the JCT undergoes continual remodeling to maintain normal resistance to aqueous humor outflow. It is believed that the TM is a major contributor of ECM proteins and evidence points towards increased ECM deposition in the outflow pathway in POAG. It is not clear how and from where the ECM components emerge to hinder the normal aqueous humor drainage. This review focuses on the involvement of the ECM in ocular hypertension and glaucoma and the mechanisms by which various ocular hypotensive drugs, both current and emerging, target ECM production, remodeling, and deposition.

The mechanical response of the porcine lens to a spinning test

The pig lens has been used as a model for presbyopia as pigs lack accommodative ability. Previous studies using microindentation have indicated that the shear modulus distribution is qualitatively similar to that of the aged human lens and that the lens does not alter its refractive power due to equatorial stretching. A lens spinning test was used to determine whether prior lens stiffness data obtained from a sectioned porcine lens were reliable and whether the testing conditions significantly influence the lens' mechanical properties. The elastic modulus distribution determined for fresh lenses closely matched that measured previously using a microindentation test. Confocal scanning laser microscopy was used to evaluate changes to the lens' structure arising from mechanical stress and following storage for up to one week.

Diadenosine tetraphosphate improves adrenergic anti-glaucomatous drug delivery and efficiency

The effect of the dinucleotide P(1), P(4)-Di (adenosine-5') tetraphosphate (Ap4A) in improving adrenergic anti-glaucomatous delivery by modifying the tight junction proteins of the corneal epithelium was evaluated. Stratified human corneal epithelial cells (HCLE) were treated with Ap4A (100 μM) for 5 min and TJ protein levels and barrier function were analysed by western blotting and transepithelial electrical resistance (TEER), respectively. Western blot experiments showed a significant reduction at 2 h (45% reduction of ZO-1 and 65% reduction of occludin protein levels) as compared to non-treated (control) cells. Two hours after Ap4A treatment, TEER values were significantly reduced (65% as compared to control levels (p < 0.001)), indicating an increase in corneal barrier permeability. Topical application of Ap4A in New Zealand white rabbits two hours before the instillation of the hypotensor compounds (the α2-adrenergic receptor agonist, brimonidine and the β-adrenergic receptor antagonist, timolol), improved the delivery of these compounds to the anterior chamber as well as their hypotensive action on the intraocular pressure. The results obtained showed that, when Ap4A was topically applied two hours before the adrenergic compounds, the concentration of brimonidine in the aqueous humour increased from 64.3 ± 5.3 nM to 240.6 ± 8.6 nM and from 58.9 ± 9.2 nM to 183.7 ± 6.8 nM in the case of timolol, which also produces a more profound effect on IOP. Therefore, Ap4A treatment results in a better entrance of adrenergic anti-glaucomatous compounds within the eye and consequently improved therapeutic efficiency by increasing corneal epithelial barrier permeability.