Glaucoma and Aqueous Veins

Ascher, K.W.

doi:10.1001/archopht.1965.00970030304027

Cited by 11 publications

(16 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…42,43 Experimentally controlled increases in IOP induced by pressure on the side of the eye, [44][45][46] ophthalmodynamometry, 47,48 or water drinking 7 result in enhanced pulsatile aqueous outflow. When IOP is reduced below its physiologic set point, pulsatile flow stops, but begins again when IOP rises to the homeostatic set point.…”

Section: Pulsatile Aqueous Outflow: a Role In Iop Homeostasismentioning

confidence: 99%

“…The first studies recognizing aqueous flow and its pulsatile character as well as multiple later studies documented that medications such as miotics 42,45,47,50,[52][53][54] and adrenergics 34,43,47,50,55 as well as prostaglandins 7 markedly increase pulsatile aqueous outflow; the increase in pulsatile flow precedes a reduction in IOP. As the IOP drops to a new homeostatic set point, pulsatility slows.…”

Section: Glaucoma Medication Management Dilemmas and Possible Phs-octmentioning

confidence: 99%

See 1 more Smart Citation

Intraocular Pressure Regulation: Findings of Pulse-Dependent Trabecular Meshwork Motion Lead to Unifying Concepts of Intraocular Pressure Homeostasis

Johnstone

2014

Journal of Ocular Pharmacology and Therapeutics

View full text Add to dashboard Cite

Intraocular pressure (IOP) is the only treatable risk factor in glaucoma, one of the world's leading causes of blindness. Mechanisms that maintain IOP within a normal range have been poorly understood in contrast to intrinsic mechanisms that regulate systemic blood pressure. Vessel walls experience continuous pulse-induced cyclic pressure and flow. Pressure-dependent wall stress and flow-dependent shear stress provide sensory signals that initiate mechanotransduction responses. The responses optimize vessel wall elasticity, compliance and lumen size, providing a feedback loop to maintain intrinsic pressure homeostasis.Aqueous humor is part of a vascular circulatory loop, being secreted into the anterior chamber of the eye from the vasculature, then returning to the vasculature by passing through the trabecular meshwork (TM), a uniquely modified vessel wall interposed between the anterior chamber and a vascular sinus called Schlemm's canal (SC). Since pressure in circulatory loops elsewhere is modulated by cyclic stresses, one might predict similar pressure modulation in the aqueous outflow system. Recent laboratory evidence in fact demonstrates that cyclic IOP changes alter aqueous outflow while increasing cellularity and contractility of TM cells. Cyclic changes also lead to alterations in gene expression, changes in cytoskeletal networks and modulation of signal transduction. A new technology, phase-based optical coherence tomography, demonstrates in vivo pulse-dependent TM motion like that elsewhere in the vasculature. Recognition of pulse-dependent TM motion provides a linkage to well-characterized mechanisms that provide pressure homeostasis in the systemic vasculature. The linkage may permit unifying concepts of pressure control and provide new insights into IOP homeostatic mechanisms.

show abstract

Section: Pulsatile Aqueous Outflow: a Role In Iop Homeostasismentioning

confidence: 99%

Section: Glaucoma Medication Management Dilemmas and Possible Phs-octmentioning

confidence: 99%

Intraocular Pressure Regulation: Findings of Pulse-Dependent Trabecular Meshwork Motion Lead to Unifying Concepts of Intraocular Pressure Homeostasis

Johnstone

2014

Journal of Ocular Pharmacology and Therapeutics

View full text Add to dashboard Cite

show abstract

“…37,38 A body of evidence indicates that the aqueous outflow from the SC is pulsatile and synchronous with IOP transients. 33,34,[39][40][41] Transients such as the cardiac pulse cannot transfer pressure gradients directly from the anterior chamber to SC because of the complex labyrinthine structure of the TM. An explanation for the pulsatile flow in the SC may be due to the trabecular tissue movement in response to the cardiac pulse.…”

Section: Introductionmentioning

confidence: 99%

Phase-sensitive optical coherence tomography characterization of pulse-induced trabecular meshwork displacement inex vivononhuman primate eyes

et al. 2012

View full text Add to dashboard Cite

Abstract. Glaucoma is a blinding disease for which intraocular pressure (IOP) is the only treatable risk factor. The mean IOP is regulated through the aqueous outflow system, which contains the trabecular meshwork (TM). Considerable evidence indicates that trabecular tissue movement regulates the aqueous outflow and becomes abnormal during glaucoma; however, such motion has thus far escaped detection. The purpose of this study is to describe anovel use of a phase-sensitive optical coherence tomography (PhS-OCT) method to assess pulsedependent TM movement. For this study, we used enucleated monkey eyes, each mounted in an anterior segment holder. A perfusion system was used to control the mean IOP as well as to provide IOP sinusoidal transients (amplitude 3 mmHg, frequency 1 pulse/second) in all experiments. Measurements were carried out at seven graded mean IOPs (5,8,10,20,30,40, and 50 mm Hg). We demonstrate that PhS-OCT is sensitive enough to image/ visualize TM movement synchronous with the pulse-induced IOP transients, providing quantitative measurements of dynamic parameters such as velocity, displacement, and strain rate that are important for assessing the biomechanical compliance of the TM. We find that the largest TM displacement is in the area closest to Schlemm's canal (SC) endothelium. While maintaining constant ocular pulse amplitude, an increase of mean IOP results in a decrease of TM displacement and mean size of the SC. These results demonstrate that the PhS-OCT is a useful imaging technique capable of assessing functional properties necessary to maintain IOP in a healthy range, offering a new diagnostic alternative for glaucoma.

show abstract

“…In the initial reports of the aqueous veins, pulsatile flow was one of the salient features and its manifestations described in remarkable detail ( Ascher, 1942a , b , c , d ; Goldmann, 1946a ; De Vries, 1947 ). Those seminal studies demonstrated that pulsatile flow occurs in response to oscillatory or cyclic IOP transients ( Fig.…”

Section: Introductionmentioning

confidence: 99%

Pulsatile flow into the aqueous veins: Manifestations in normal and glaucomatous eyes

Johnstone

Martin

Jamil

2011

Experimental Eye Research

102

120

View full text Add to dashboard Cite

The aqueous outflow system is unique because nowhere else can the pattern of flow of an extravascular fluid be directly observed as it returns to the vascular system. Such observations reveal that aqueous flow both from Schlemm’s canal into the aqueous veins and from the aqueous veins into the episcleral veins is pulsatile. Pulsatile aqueous flow mechanisms are observable in vivo not only in normal and but also in glaucomatous eyes. A series of specific patterns accompany the pulsatile mixing of aqueous with blood in the episcleral veins. These directly observable patterns of pulsatile flow are synchronous with intraocular pressure (IOP) transients induced by the cardiac pulse, blinking and eye movement. Patterns of pulsatile flow are altered by events that increase IOP such as pressure on the side of the eye, tonography and water drinking. Pulsatile flow stops when IOP is reduced below its resting level, but begins again when IOP returns to the resting level. Pulsatile flow reduction probably results from the intrinsic reduction of pulse amplitude at a lower IOP, and may thus provide a passive mechanism to maintain short-term homeostasis. Thus modulation of the pulsatile flow phenomenon appears to maintain a homeostatic IOP setpoint. Visible pulsatile flow abnormalities develop in glaucoma patients. Medications that reduce IOP through improvement in outflow do so through pulsatile flow mechanisms. Laboratory studies have demonstrated that cyclic stresses in outflow tissues alter signaling pathways, cytoskeletal responses, extracellular matrix composition and cytokine secretion. How physiologic pulse transients orchestrate cellular responses and how cellular responses identified in the laboratory may in turn regulate pulsatile aqueous outflow is unknown. Linkage of laboratory and in vivo observations await an improved understanding of how cellular and extracellular structures within the outflow system are able to generate an aqueous pulse wave. The purpose of the current report is to provide a summary of in vivo IOP-induced patterns of cyclic flow that can be used as part of a framework for interpretation of responses to cyclic stresses identified in the laboratory.

show abstract

Glaucoma and Aqueous Veins

Cited by 11 publications

References 0 publications

Intraocular Pressure Regulation: Findings of Pulse-Dependent Trabecular Meshwork Motion Lead to Unifying Concepts of Intraocular Pressure Homeostasis

Intraocular Pressure Regulation: Findings of Pulse-Dependent Trabecular Meshwork Motion Lead to Unifying Concepts of Intraocular Pressure Homeostasis

Phase-sensitive optical coherence tomography characterization of pulse-induced trabecular meshwork displacement inex vivononhuman primate eyes

Pulsatile flow into the aqueous veins: Manifestations in normal and glaucomatous eyes

Contact Info

Product

Resources

About