Functional Anatomy of the Outflow Facilities

Ultrasound biomicroscopy analysis of ciliary muscle dynamics and its relation to intra-ocular pressure after phacoemulsification in dogs

Introduction

This study investigates the relationship between ciliary muscle dynamics, thickness, and the regulation of intraocular pressure (IOP), focusing on the progression of cataracts and changes post-phacoemulsification. It explores how these factors impact canine ocular health, particularly in the context of cataract development and subsequent surgical intervention.

Materials and methods

Data was collected using Ultrasound Biomicroscopy (UBM) from dogs at the Veterinary Medical Teaching Hospital of Chungbuk National University, Korea. The study involved 57 eyes from 35 dogs, categorized into five groups: 13 normal eyes, 14 with incipient cataracts, 12 with immature cataracts, 6 with mature cataracts, and 12 post-phacoemulsification. UBM measurements assessed various ciliary muscle parameters including ciliary body axial length (CBAXL), ciliary process-sclera angle (CPSA), longitudinal fibers of ciliary muscle thickness (Lf-CMT), and longitudinal and radial fibers of ciliary muscle thickness (LRf-CMT).

Results

Findings indicated a decrease in CBAXL and an increase in Lf-CMT as cataracts progressed in severity. Post-phacoemulsification, there was a notable increase in CBAXL and a decrease in CPSA, Lf-CMT, and LRf-CMT, compared to both cataractous and normal eyes. Regression analysis revealed a significant positive association between CBAXL and IOP, alongside a negative association between Lf-CMT and IOP. These findings suggest that variations in ciliary muscle dynamics and thickness, as influenced by cataract progression and phacoemulsification, have distinct impacts on intraocular pressure.

Discussion

The study proposes that phacoemulsification leads to ciliary muscle contraction, causing an inward and anterior movement of the ciliary muscle. This movement results in the narrowing of the ciliary cleft and constriction of the unconventional outflow pathway, potentially causing an increased risk of glaucoma post-surgery. Our research contributes to understanding the anatomical and physiological changes in the canine eye following cataract surgery and underscores the importance of monitoring IOP and ciliary muscle dynamics in these patients.

Comparative study of the ciliary body and iris morphology in the anterior eye chamber of five different vertebrate classes

One crucial component of the optical system is the ciliary body (CB). This body secretes the aqueous humour, which is essential to maintain the internal eye pressure as well as the clearness of the lens and cornea. The histological study was designed to provide the morphological differences of CB and iris in the anterior eye chambers of the following vertebrate classes: fish (grass carp), amphibians (Arabian toad), reptiles (semiaquatic turtle, fan-footed gecko, ocellated skink, Egyptian spiny-tailed lizard, Arabian horned viper), birds (common pigeon, common quail, common kestrel), and mammals (BALB/c mouse, rabbit, golden hamster, desert hedgehog, lesser Egyptian jerboa, Egyptian fruit bat). The results showed distinct morphological appearances of the CB and iris in each species, ranging from fish to mammals. The present comparative study concluded that the morphological structure of the CB and iris is the adaptation of species to either their lifestyle or survival in specific habitats.

Prevalence of pre-iridal monocellular and fibrovascular membranes in canine globes affected with congenital glaucoma associated with anterior segment dysgenesis, primary glaucoma associated with goniodysgenesis, and secondary glaucoma

Objectives

The objectives of this study were to (i) evaluate the prevalence of pre-iridal monocellular and fibrovascular membranes in canine globes affected with congenital glaucoma associated with anterior segment dysgenesis (ASD), primary glaucoma associated with goniodysgenesis (GD), and secondary glaucoma, and (ii) examine the associations between monocellular and fibrovascular membranes by breed, gender, age and histopathologic ocular changes on light microscopic examination.

Methods

Records of dogs who had eyes enucleated due to blindness and uncontrolled glaucoma were reviewed. Glaucoma was categorized clinically and histologically into three groups: congenital/ASD, primary/GD, and secondary glaucoma. The presence or absence and type of pre-iridal membrane (monocellular or fibrovascular) and other intraocular histologic findings were reviewed and compared statistically for each group.

Results

In total, 108 canine globes (101 dogs) were included. Pre-iridal monocellular membranes were identified with light microscopy in 10 out of 19 congenital/ASD, 29 out of 40 primary, and 23 out of 49 secondary glaucoma globes. Fibrovascular membranes were observed in 3 out of 19 congenital/ASD, 9 out of 40 in primary, and 24 out of 49 secondary glaucoma globes. There were no associations between the type of membrane and breed, gender, or age. Peripheral anterior synechiae were more common in globes with fibrovascular membranes, and uveal atrophy was more common in globes with monocellular membranes.

Conclusion

Pre-iridal monocellular membranes are common in all types of canine glaucoma. They are identified with light microscopy most easily in cases of primary glaucoma, and they are masked by pre-iridal fibrovascular membranes in other forms of glaucoma.

Evaluation of ciliary cleft changes after phacoemulsification using ultrasound biomicroscopy in dogs with cataracts

Introduction

Glaucoma is one of the most serious complications that causes irreversible blindness after phacoemulsification in dogs; however, a clear mechanism has not been elucidated. This study aimed to analyse the possible anatomical factors associated with glaucoma after phacoemulsification using parameters that reflect the anatomical characteristics of dogs.

Materials and methods

A total of 69 eyes of 48 dogs were included in this study. The patients were divided into three groups: normal eye (n = 18), cataract (n = 39), and post-phacoemulsification for at least 2 months after surgery (post-phaco, n = 12). For further analysis, the dogs were subdivided into two groups according to cataract stage: phacoemulsification non-candidate and candidate groups. Non-cataracts and incipient cataracts were categorized into the non-candidate group, whereas immature and mature cataracts were categorized into the candidate group. Measurements of the ciliary cleft parameters, including the area of the ciliary cleft (CCA), length of the ciliary cleft (CCL), width of the ciliary cleft (CCW), iridocorneal angle, and angle opening distance, were obtained using ultrasound biomicroscopy.

Results

CCA, CCL, and CCW were significantly higher in the candidate group than in the non-candidate group. CCA, CCL, and CCW were significantly reduced in the post-phaco group compared to those in the cataract group. Based on these results, we found that the ciliary cleft expanded in cataract-affected eyes and narrowed after phacoemulsification. This may indicate that the space between the trabecular meshworks became narrower, potentially leading to an increase in the resistance of the aqueous humor.

Conclusion

A narrowed ciliary cleft after phacoemulsification may be an anatomical factor associated with glaucoma.

The Clinical Approach to Canine Glaucoma

This article provides a simplified approach to diagnosis and clinical decision making in cases of canine glaucoma for the general practitioner. An overview of the anatomy, physiology, and pathophysiology related to canine glaucoma is provided as a foundation. Classifications of glaucoma based on cause are described as congenital, primary, and secondary, and a discussion of key clinical examination findings is provided to guide appropriate therapy and prognostication. Finally, a discussion of emergency and maintenance therapy is provided.

Immunology and Pathology in Ocular Drug Development

Clear vision is dependent on features that protect the anatomical integrity of the eye (cornea and sclera) and those that contribute to internal ocular homeostasis by conferring hemangiogenic (avascular tissues and antiangiogenic factors), lymphangiogenic (lack of draining lymphatics), and immunologic (tight junctions that form blood-ocular barriers, immunosuppressive cells, and modulators) privileges. The later examples are necessary components that enable the eye to maintain an immunosuppressive environment that responds to foreign invaders in a deviated manner, minimizing destructive inflammation that would impair vision. These conditions allowed for the observations made by Medawar, in 1948, of delayed rejection of allogenic tissue grafts in the anterior chamber of mouse eye and permit the sequestration of foreign invaders (eg, Toxoplasma gondii) within the retina of healthy individuals. Yet successful development of intraocular drugs (biologics and delivery devices) has been stymied by adverse ocular pathology, much of which is driven by immune pathways. The eye can be intolerant of foreign protein irrespective of delivery route, and endogenous ocular cells have remarkable plasticity when recruited to preserve visual function. This article provides a review of current understanding of ocular immunology and the potential role of immune mechanisms in pathology observed with intraocular drug delivery.

Aqueous Humor Outflow Requires Active Cellular Metabolism in Mice

Purpose

Conventional wisdom posits that aqueous humor leaves the eye by passive bulk flow without involving energy-dependent processes. However, recent studies have shown that active processes, such as cell contractility, contribute to outflow regulation. Here, we examine whether inhibiting cellular metabolism affects outflow facility in mice.

Methods

We measured outflow facility in paired enucleated eyes from C57BL/6J mice using iPerfusion. We had three Experimental Sets: ES1, perfused at 35°C versus 22°C; ES2, perfused with metabolic inhibitors versus vehicle at 35°C; and ES3, perfused at 35°C versus 22°C in the presence of metabolic inhibitors. Inhibitors targeted glycolysis and oxidative phosphorylation (2-deoxy-D-glucose, 3PO and sodium azide). We also measured adenosine triphosphate (ATP) levels in separate murine anterior segments treated like ES1 and ES2.

Results

Reducing temperature decreased facility by 63% [38%, 78%] (mean [95% confidence interval (CI)], n = 10 pairs; P = 0.002) in ES1 after correcting for changes in viscosity. Metabolic inhibitors reduced facility by 21% [9%, 31%] (n = 9, P = 0.006) in ES2. In the presence of inhibitors, temperature reduction decreased facility by 44% [29%, 56%] (n = 8, P < 0.001) in ES3. Metabolic inhibitors reduced anterior segment adenosine triphosphate (ATP) levels by 90% [83%, 97%] (n = 5, P<<0.001), but reducing temperature did not affect ATP.

Conclusions

Inhibiting cellular metabolism decreases outflow facility within minutes. This implies that outflow is not entirely passive, but depends partly on energy-dependent cellular processes, at least in mice. This study also suggests that there is a yet unidentified mechanism, which is strongly temperature-dependent but metabolism-independent, that is necessary for nearly half of normal outflow function in mice.

NGF in Inflammatory and Neurodegenerative Diseases of the Eye: New Findings Supporting Neuroprotection and Proper Tissue Remodeling in Vitreoretinal Disorders

Nerve growth factor (NGF) plays a crucial role in retinal disorders, as suggested by in vitro/in vivo models. The major effect embraces the neuroprotective activity on retinal ganglion cells (RGCs) undergoing degeneration, as observed in experimental diabetic retinopathy, age-related and diabetic macular degeneration, and some vitreoretinal diseases. Focused experiments suggested that locally applied NGF (intravitreal delivery) not only allowed the counteraction of RGC degeneration but also provided data for a whole retina restoration. The currently available retinal microsurgery allows the collection of human aqueous and more interesting vitreous (vitreal reflux) humors. The recent biomolecular analysis highlights the possibility to identify disease-associated biomarkers and allow the monitoring of retinal impairments with sustain to the retinal imaging. Coupled to other soluble mediators, NGF has been quantified in aqueous (slightly expressed) from diabetic retinopathy-suffering patients (cataract surgery) and vitreal reflux (significantly impaired) of diabetic macular degeneration-suffering patients (intravitreal surgery). Although the reasons of these NGF impairments are not fully comprehended, some retinal cells (glial cells, bipolar neurons, and RGCs) have been recognized partially responsible for these local changes.Taken together, the recent progress in the ocular microsurgeries might be associated with sampling of small amount of ocular humors, allowing the collection of biochemical information about diseased retina and the monitoring of treatment. The chance to detect NGF and likewise other neuroprotective or pro-/anti-inflammatory factors in these fluids would open to the possibility to identify biomarkers of early diagnosis or monitoring of retinal disease evolution/therapy (precision medicine).

Gonioscopic iridocorneal angle morphology and incidence of postoperative ocular hypertension and glaucoma in dogs following cataract surgery

PURPOSE

To investigate the relationship between gonioscopic iridocorneal angle (ICA) morphology and the incidence of postoperative ocular hypertension (POH) and postoperative glaucoma in dogs undergoing cataract surgery.

ANIMALS STUDIED

Retrospective analysis of 138 eyes of 78 canine patients who underwent phacoemulsification at North Carolina State University from December 1, 2015 through April 30, 2017.

METHODS

Medical records of all phacoemulsification patients with preoperative RetCam gonioscopic images were reviewed for preoperative, intraoperative, and postoperative variables. Gonioscopic angle indices were calculated using a novel (ZibWest) angle grading system, and these indices were analyzed for outcome-related significance.

RESULTS

Increased surgeon experience was associated with increased probability of POH and vision loss. Higher average ZibWest Angle indices (ie, more open angles with less pectinate ligament dysplasia/ abnormality) were associated with a significantly decreased probability of medically unresponsive glaucoma. Increased patient age was significantly associated with an increased probability of both postoperative glaucoma and vision loss. Female dogs were significantly more likely to experience postoperative glaucoma compared to male dogs. Increased surgery time was significantly associated with increased probability of vision loss.

CONCLUSIONS

The ZibWest angle index may predict increased risk for developing medically unresponsive glaucoma with cataract surgery. Female sex, and increased patient age, surgical time, and surgeon experience were associated with increased postoperative morbidity.

An In Vitro Bovine Cellular Model for Human Schlemm's Canal Endothelial Cells and Their Response to TGFβ Treatment

Purpose

Due to the limited availability of primary human Schlemm's canal (SC) endothelial cells, we aimed to develop an in vitro cellular model using the angular aqueous plexus (AAP) cells from bovine eyes.

Methods

We harvested a mixture of cells from the trabecular meshwork region including AAP loops from multiple donors, followed by puromycin treatment and immunostaining of Von Willebrand factor and vascular endothelial (VE)-cadherin to confirm identity. Previously identified differentially expressed genes in glaucomatous SC cells were examined in non-glaucomatous SC cells (n = 3) under 0% or 15% equibiaxial strain for 24 hours using droplet digital polymerase chain reaction (ddPCR) and analyzed using the Ingenuity Pathway Analysis (IPA) software application to identify upstream regulators. To compare the cellular responses to candidate regulators of these mechanoresponsive genes, AAP and human SC cells (n = 3) were treated with 5 or 10 ng/mL transforming growth factor beta-2 (TGFβ2) for 24 or 48 hours, followed with expression profiling using real-time PCR or ddPCR.

Results

We found that the isolated AAP cells displayed uniform cobblestone-like morphology and positive expression of two endothelial markers. In stretched SC cells, nine glaucoma-related genes were upregulated, and IPA implicated TGFβ as a potential upstream regulator. The effects of TGFβ2 treatment were similar for both AAP and SC cells in a dose- and time-dependent manner, activating TGFBR1 and SMAD2, inhibiting BMP4, and altering expression of three glaucoma-related genes (DCN,EZR, and CYP1B1).

Conclusions

Bovine AAP cells may serve as an alternative cellular model of human SC cells.

Translational Relevance

These AAP cells may be used to study the functional pathways related to the outflow facility.

Effects of 0.02% netarsudil ophthalmic solution on intraocular pressure of normotensive dogs

OBJECTIVES

To evaluate the effect of QD or BID 0.02% netarsudil ophthalmic solution (Aerie Pharmaceuticals) on intraocular pressure (IOP) in normotensive dogs and to describe any adverse effects.

ANIMALS STUDIED

Normotensive Labrador retriever dogs were included in this study: 10 received netarsudil in one eye and artificial tears in the contralateral eye QD, and 10 received netarsudil in one eye and artificial tears in the contralateral eye BID.

PROCEDURES

Intraocular pressure curves were acquired over a 3-day acclimation period, 5-day dosing period (QD or BID-10 dogs/group), and 3-day recovery period. Toxicity was assessed daily using slit-lamp biomicroscopy and the semiquantitative preclinical ocular toxicology scoring system.

RESULTS

Once-daily dosing did not lower IOP over the entire 5-day dosing period (95% CI 0.1 to -0.9 mm Hg, P = .20) or on the last day of dosing (95% CI 0.4 to -0.9 mm Hg, P = .65). Twice-daily dosing resulted in a statistically significant, but clinically unimportant, IOP reduction over the entire 5-day dosing period (-0.6 mm Hg; 95% CI 0.05 to -1.1 mm Hg, P = .02) and on the last day of dosing (-0.9 mm Hg; 95% CI 0.2 to -1.5 mm Hg, P = .003). Adverse events were limited to transient mild-to-moderate conjunctival hyperemia during the dosing phase in eyes receiving netarsudil vs control (P < .0001).

CONCLUSIONS

Netarsudil 0.02% ophthalmic solution twice daily resulted in a small, statistically significant, but clinically unimportant, IOP reduction in normotensive dogs. Future studies should investigate efficacy in glaucomatous dogs.

The Intraocular Pressure-Lowering Effect of Persimmon leaves (Diospyros kaki) in a Mouse Model of Glaucoma

The aim of this study was to evaluate the pharmacological efficacy of persimmon leaves in two glaucoma models, microbeads-induced ocular hypertension (OHT) and DBA/2 mouse. Thus, we demonstrated that Ethanol Extract of Diospyros kaki (EEDK) reduced elevated intraocular pressure (IOP) in both mouse models of glaucoma by measurements with a tonometer. In particular, we revealed that retinal ganglion cell loss and optic nerve damage caused by IOP elevation were markedly diminished as assessed by TUNEL assay, H&E staining, and fluorescent staining, while the expression of soluble guanylate cyclase (sGCα-1) increased, when EEDK was administered, as revealed by western blot. Moreover, the b-wave magnitude indicating functional scotopic vision was significantly improved in EEDK-administered DBA/2 mice during the 10-week follow-up study, as observed with electroretinography. Collectively, our results suggested that EEDK could be an effective therapeutic and IOP-lowering agent for preventing and treating retinal degenerative diseases such as glaucoma.

Post-traumatic Intraocular Leiomyosarcoma in a Domestic Bovine Calf (Bos primigenius taurus)

The present report describes a case of a post-traumatic ocular leiomyosarcoma in a calf (Bos primigenius taurus) including clinical, histopathological and immunohistochemical features. Following a traumatic episode, the animal developed opacification of the lens and shrinkage of the eye. Subsequently, the ocular lesion increased in size over a period of 6 weeks and reached up to 16 cm in diameter with infiltration into the cranium. At necropsy examination, the kidneys, liver and spleen exhibited multiple firm white metastases up to 2 cm in diameter. The mass was composed of closely-packed streams and bundles of neoplastic cells, which immunohistochemically expressed vimentin and alpha smooth muscle actin. Based on the anamnestic data, morphological appearance, distribution and immunohistochemical results, a diagnosis of a post-traumatic intraocular leiomyosarcoma was made. The tumour may have originated from cells lining the pectinate ligament of the ciliary body.

An analysis of anterior segment development in the chicken eye

Precise anterior segment (AS) development in the vertebrate eye is essential for maintaining ocular health throughout life. Disruptions to genetic programs can lead to severe structural AS disorders at birth, while more subtle AS defects may disrupt the drainage of ocular fluids and cause dysregulation of intraocular pressure homeostasis, leading to progressive vision loss. To date, the mouse has served as the major model to study AS development and pathogenesis. Here we present an accurate histological atlas of chick AS formation throughout eye development, with a focus on the formation of drainage structures. We performed expression analyses for a panel of known AS disorder genes, and showed that chick PAX6 was localized to cells of neural retina and surface ectoderm derived structures, displaying remarkable similarity to the mouse. We provide a comparison to mouse and humans for chick AS developmental sequences and structures and confirm that AS development shares common features in all three species, although the main AS structures in the chick are developed prior to hatching. These features enable the unique experimental advantages inherent to chick embryos, and we therefore propose the chick as an appropriate additional model for AS development and disease.

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.

Discovery and Preclinical Development of Netarsudil, a Novel Ocular Hypotensive Agent for the Treatment of Glaucoma

PURPOSE

Rho-associated protein kinase (ROCK) inhibitors lower intraocular pressure (IOP) by increasing aqueous outflow through the trabecular meshwork (TM). The preclinical characterization of netarsudil, a new ROCK/norepinephrine transporter (NET) inhibitor currently in clinical development, is presented herein.

METHODS

The kinase inhibitory activity of netarsudil was compared to its esterase metabolite, netarsudil-M1, and 3 other ROCK inhibitors using a commercially available kinase assay kit. Disruption of actin stress fibers was measured in primary porcine TM cells and disruption of focal adhesions in transformed human TM (HTM) cells. Induction of fibrosis markers after exposure to transforming growth factor-β2 (TGF-β2) was conducted in primary HTM cells. Ocular hypotensive activity and tolerability of topical formulations were evaluated in normotensive Dutch Belted rabbits and Formosan Rock monkeys. In vitro corneal metabolism assays were conducted using dog, pig, rabbit, monkey, and human corneas. In vivo ocular pharmacokinetics was studied in Dutch Belted rabbits.

RESULTS

Netarsudil inhibited kinases ROCK1 and ROCK2 with a Ki of 1 nM each, disrupted actin stress fibers and focal adhesions in TM cells with IC50s of 79 and 16 nM, respectively, and blocked the profibrotic effects of TGF-β2 in HTM cells. Netarsudil produced large reductions in IOP in rabbits and monkeys that were sustained for at least 24 h after once daily dosing, with transient, mild hyperemia observed as the only adverse effect.

CONCLUSION

Netarsudil is a novel ROCK/NET inhibitor with high potency in biochemical and cell-based assays, an ability to produce large and durable IOP reductions in animal models, and favorable pharmacokinetic and ocular tolerability profiles.

Microscopic Lesions in Canine Eyes with Primary Glaucoma

Although the clinical classification of primary glaucoma in dogs is quite simple, the phenotypes of glaucoma in most of the species are indeed multiple. Ophthalmologists can often evaluate the dynamic changes of clinical signs at different times in the course of the disease, whereas pathologists are often presented with globes that have undergone abundant therapies and are at the end stage. Therefore, an open collaboration between clinicians and pathologists can produce the most accurate interpretation in the pathology report and improve patient outcomes. This article focuses on the histomorphologic elements that characterize, and are important to, canine primary glaucomas.