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Jennifer H Siggers - One of the best experts on this subject based on the ideXlab platform.
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Investigation of the motion of a viscous fluid in the Vitreous cavity induced by eye rotations and implications for drug delivery.
Physics in Medicine and Biology, 2013Co-Authors: Andrea Bonfiglio, Rodolfo Repetto, Jennifer H Siggers, Alessandro StocchinoAbstract:Intravitreal drug delivery is a commonly used treatment for several retinal diseases. The objective of this research is to characterize and quantify the role of the Vitreous humor motion, induced by saccadic movements, on drug transport processes in the Vitreous Chamber. A Perspex model of the human Vitreous Chamber was created, and filled with a purely viscous fluid, representing eyes with a liquefied Vitreous humor or those containing viscous tamponade fluids. Periodic movements were applied to the model and the resulting three-dimensional (3D) flow fields were measured. Drug delivery within the Vitreous Chamber was investigated by calculating particle trajectories using integration over time of the experimental velocity fields. The motion of the Vitreous humor generated by saccadic eye movements is intrinsically 3D. Advective mass transport largely overcomes molecular diffusive transport and is significantly anisotropic, leading to a much faster drug dispersion than in the case of stationary Vitreous humor. Disregarding the effects of Vitreous humor motion due to eye movements when predicting the efficiency of drug delivery treatments leads to significant underestimation of the drug transport coefficients, and this, in turn, will lead to significantly erroneous predictions of the concentration levels on the retina.
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shape change of the Vitreous Chamber influences retinal detachment and reattachment processes is mechanical stress during eye rotations a factor
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Julia Meskauskas, Rodolfo Repetto, Jennifer H SiggersAbstract:PURPOSE: We aim to understand how mechanical causation influences retinal detachment and reattachment processes. In particular, myopes suffer retinal detachment more frequently than emmetropes, and following a retinal detachment, scleral buckling promotes retinal reattachment. We test the hypothesis that stresses arising from saccadic eye rotations are involved in the processes, and that the alteration in the stress due to the change in the Vitreous Chamber geometry is sufficient to explain the phenomena. METHODS: The Vitreous Chamber of the eye has an approximately spherical shape and it is filled with Vitreous humor. We developed a mathematical model, treating the Vitreous Chamber in emmetropic and myopic eyes as a spheroid and in eyes subjected to scleral buckling as a sphere with a circumferential indentation. We assume that the eye performs prescribed small-amplitude, periodic, torsional rotations and we solve semi-analytically for the fluid pressure, velocity, and stress distributions. RESULTS: The shape of the Vitreous Chamber has a large effect on the retinal stress. The Vitreous and the retina of a highly myopic eye continuously experience shear stresses significantly higher than those of an emmetropic eye. An eye fitted with a scleral buckle experiences large stress levels localized around the buckle. CONCLUSIONS: Our results provide a mechanical explanation for the more frequent occurrence of posterior Vitreous detachment and retinal detachment in myopic eyes. To understand how the stress distribution in a buckled eye facilitates reattachment, an additional model of the details of the reattachment process should be coupled to this model.
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in vitro simulations of drug delivery in the Vitreous Chamber of the eye
ASME 2012 Summer Bioengineering Conference Parts A and B, 2012Co-Authors: Andrea Bonfiglio, Rodolfo Repetto, Alessandro Stocchino, Jennifer H SiggersAbstract:The Vitreous Chamber has an approximately spherical shape, and is filled with Vitreous humor, a transparent material with viscoelastic properties. The Vitreous humor has the mechanical roles of supporting the eye shape, promoting the adherence between the retina and the choroid, and acting as a barrier between the anterior and posterior segments of the eye for transport of heat and molecules [1]. Often, in elderly people, the Vitreous humor has almost Newtonian properties as a consequence of a liquefaction process consisting of degradation of the collagenous framework of the gel. Moreover, after vitrectomy the Vitreous humor is sometimes replaced with viscous tamponade fluids (typically silicone oils). Since intra-vitreal drug injection is increasingly used to treat retinal diseases, and the efficacy of this procedure depends on molecular transport processes after the injection, much of the biomechanical research on the Vitreous humor has focused on understanding transport processes in the Vitreous Chamber. Many authors have considered purely diffusive transport or alternatively diffusion with advective transport due to creeping bulk flow only [2,3]. However, when the Vitreous is liquefied, rotational motion of the eye has been shown to induce significant fluid flow, which plays a fundamental role for drug delivery in the Vitreous Chamber [4–7]. The most significant contribution to mass transport is due to the generation of a steady streaming flow, i.e. a steady flow resulting from the non-linearity in the equations. This flow component gives rise to a slow particle drift that becomes dominant over long times.Copyright © 2012 by ASME
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Theoretical Model of the Dynamic Stress on the Retina During Eye Rotations
ASME 2012 Summer Bioengineering Conference Parts A and B, 2012Co-Authors: Julia Meskauskas, Rodolfo Repetto, Jennifer H SiggersAbstract:The Vitreous humor is the transparent gel-like material that fills the Vitreous Chamber, the largest Chamber of the eye, which has an approximately spherical shape. The viscoelastic properties of the Vitreous humor have been studied by several authors [1–3].Copyright © 2012 by ASME
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mixing processes in the Vitreous Chamber induced by eye rotations
Physics in Medicine and Biology, 2010Co-Authors: Alessandro Stocchino, Rodolfo Repetto, Jennifer H SiggersAbstract:In this paper, we study a model of flow in the Vitreous humour in the posterior Chamber of the human eye, induced by saccadic eye rotations. We concentrate on the effect of the shape of the Chamber upon the mixing properties of the induced flows. We make particle image velocimetry measurements of the fluid velocity in a transparent plastic (Perspex) model of the posterior Chamber during sinusoidal torsional oscillations about a vertical axis. We use a Newtonian fluid to model the Vitreous humour, which is most realistic when either the Vitreous humour is liquefied or has been replaced by purely viscous tamponade fluids. The model of the posterior Chamber is a sphere with an indentation, representing the effect of the lens. In spite of the purely periodic forcing, a steady streaming flow is generated, which plays a fundamental role in the mixing processes in the domain. The streaming flow differs markedly from that in a perfect sphere, and its topological characteristics change substantially as the frequency of oscillation varies. We discuss the flow characteristics in detail and show that, for physiological parameter values, the Peclet number (based on a suitable measure of the steady streaming velocity) is large, suggesting that advection strongly dominates over diffusion for mass transport phenomena. We also compute particle trajectories based on the streaming velocity and use these to investigate the stirring properties of the flow.
Rodolfo Repetto - One of the best experts on this subject based on the ideXlab platform.
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mathematical models of Vitreous humour dynamics and retinal detachment
2019Co-Authors: Rodolfo Repetto, Mariia DvoriashynaAbstract:The Vitreous humour is a gel-like substance, which fills the Vitreous Chamber at the posterior part of the eye. It is a clear transparent material that can be mechanically characterised as a visco-elastic fluid. The Vitreous has the important role of holding the retina in contact with the retinal pigment epithelium. During Vitreous motion vitreoretinal tractions are generated and this might potentially lead to retinal detachment (RD). Studying the Vitreous mechanical behaviour is thus relevant for understanding the physiology and pathophysiology of the eye.
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A model for the linear stability of the interface between aqueous humor and Vitreous substitutes after vitreoretinal surgery
Physics of Fluids, 2014Co-Authors: Krystyna Isakova, Rodolfo Repetto, Jan O. Pralits, Mario RomanoAbstract:We consider the motion of two immiscible viscous fluids induced by periodic oscillations of a flat solid surface along its plane. The interface between the two fluids is parallel to the solid wall; one fluid occupies the region between the wall and the interface and the other extends from the interface to infinity. We study numerically the linear stability of the interface with respect to two-dimensional perturbations using the normal mode analysis and assuming quasi-steady flow conditions. The analysis is motivated by the need of understanding the behavior of Vitreous substitutes inserted in the Vitreous Chamber of the eye after vitrectomy. This is a common surgical procedure adopted to treat retinal detachments, whereby the Vitreous humor is removed from the eye and replaced by fluids immiscible with water. Owing to their hydrophobic nature, Vitreous substitutes coexist in the Vitreous Chamber with a certain amount of aqueous humor (the fluid produced in the anterior part of the eye) and, typically, a t...
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Mechanical Models of the Dynamics of Vitreous Substitutes
BioMed Research International, 2014Co-Authors: Krystyna Isakova, Rodolfo Repetto, Jan O. Pralits, Mario RomanoAbstract:We discuss some aspects of the fluid dynamics of Vitreous substitutes in the Vitreous Chamber, focussing on the flow induced by rotations of the eye bulb. We use simple, yet not trivial, theoretical models to highlight mechanical concepts that are relevant to understand the dynamics of Vitreous substitutes and also to identify ideal properties for Vitreous replacement fluids. We first recall results by previous authors, showing that the maximum shear stress on the retina grows with increasing viscosity of the fluid up to a saturation value. We then investigate how the wall shear stress changes if a thin layer of aqueous humour is present in the Vitreous Chamber, separating the retina from the Vitreous replacement fluid. The theoretical predictions show that the existence of a thin layer of aqueous is sufficient to substantially decrease the shear stress on the retina. We finally discuss a theoretical model that predicts the stability conditions of the interface between the aqueous and a Vitreous substitute. We discuss the implications of this model to understand the mechanisms leading to the formation of emulsion in the Vitreous Chamber, showing that instability of the interface is possible in a range of parameters relevant for the human eye.
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Investigation of the motion of a viscous fluid in the Vitreous cavity induced by eye rotations and implications for drug delivery.
Physics in Medicine and Biology, 2013Co-Authors: Andrea Bonfiglio, Rodolfo Repetto, Jennifer H Siggers, Alessandro StocchinoAbstract:Intravitreal drug delivery is a commonly used treatment for several retinal diseases. The objective of this research is to characterize and quantify the role of the Vitreous humor motion, induced by saccadic movements, on drug transport processes in the Vitreous Chamber. A Perspex model of the human Vitreous Chamber was created, and filled with a purely viscous fluid, representing eyes with a liquefied Vitreous humor or those containing viscous tamponade fluids. Periodic movements were applied to the model and the resulting three-dimensional (3D) flow fields were measured. Drug delivery within the Vitreous Chamber was investigated by calculating particle trajectories using integration over time of the experimental velocity fields. The motion of the Vitreous humor generated by saccadic eye movements is intrinsically 3D. Advective mass transport largely overcomes molecular diffusive transport and is significantly anisotropic, leading to a much faster drug dispersion than in the case of stationary Vitreous humor. Disregarding the effects of Vitreous humor motion due to eye movements when predicting the efficiency of drug delivery treatments leads to significant underestimation of the drug transport coefficients, and this, in turn, will lead to significantly erroneous predictions of the concentration levels on the retina.
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shape change of the Vitreous Chamber influences retinal detachment and reattachment processes is mechanical stress during eye rotations a factor
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Julia Meskauskas, Rodolfo Repetto, Jennifer H SiggersAbstract:PURPOSE: We aim to understand how mechanical causation influences retinal detachment and reattachment processes. In particular, myopes suffer retinal detachment more frequently than emmetropes, and following a retinal detachment, scleral buckling promotes retinal reattachment. We test the hypothesis that stresses arising from saccadic eye rotations are involved in the processes, and that the alteration in the stress due to the change in the Vitreous Chamber geometry is sufficient to explain the phenomena. METHODS: The Vitreous Chamber of the eye has an approximately spherical shape and it is filled with Vitreous humor. We developed a mathematical model, treating the Vitreous Chamber in emmetropic and myopic eyes as a spheroid and in eyes subjected to scleral buckling as a sphere with a circumferential indentation. We assume that the eye performs prescribed small-amplitude, periodic, torsional rotations and we solve semi-analytically for the fluid pressure, velocity, and stress distributions. RESULTS: The shape of the Vitreous Chamber has a large effect on the retinal stress. The Vitreous and the retina of a highly myopic eye continuously experience shear stresses significantly higher than those of an emmetropic eye. An eye fitted with a scleral buckle experiences large stress levels localized around the buckle. CONCLUSIONS: Our results provide a mechanical explanation for the more frequent occurrence of posterior Vitreous detachment and retinal detachment in myopic eyes. To understand how the stress distribution in a buckled eye facilitates reattachment, an additional model of the details of the reattachment process should be coupled to this model.
Jian Ge - One of the best experts on this subject based on the ideXlab platform.
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Effects of confined space and near vision stimulation on refractive status and Vitreous Chamber depth in adolescent rhesus monkeys
Science China-life Sciences, 2010Co-Authors: Yunxia Leng, Zhikuan Yang, Keming Yu, Zheng Li, Xingwu Zhong, Shaochong Zhang, Jian GeAbstract:This study aimed to investigate the effects of sustained near vision stimulation, on the refractive development and elongation of the Vitreous Chamber in adolescent rhesus monkeys. A total of 12 adolescent rhesus monkeys (1.5–2.0 years old) were randomly assigned to 3 groups. In groups A (n=4) and B (n=4), monkeys were reared in close-vision cages for 8 and 4 h d−1, respectively; tiny granules were added on the cage floor to avoid visual deprivation and to encourage near gaze. In group C (n=4), monkeys were reared in open-vision cages, with non-granule food as a control. Vitreous Chamber depth, refractive status, and corneal refractive power were assessed over 18 months. Paired t-test was used to compare the differences and a P-value
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effects of confined space and near vision stimulation on refractive status and Vitreous Chamber depth in adolescent rhesus monkeys
Science China-life Sciences, 2010Co-Authors: Yunxia Leng, Zhikuan Yang, Keming Yu, Zheng Li, Xingwu Zhong, Shaochong Zhang, Jian GeAbstract:This study aimed to investigate the effects of sustained near vision stimulation, on the refractive development and elongation of the Vitreous Chamber in adolescent rhesus monkeys. A total of 12 adolescent rhesus monkeys (1.5–2.0 years old) were randomly assigned to 3 groups. In groups A (n=4) and B (n=4), monkeys were reared in close-vision cages for 8 and 4 h d−1, respectively; tiny granules were added on the cage floor to avoid visual deprivation and to encourage near gaze. In group C (n=4), monkeys were reared in open-vision cages, with non-granule food as a control. Vitreous Chamber depth, refractive status, and corneal refractive power were assessed over 18 months. Paired t-test was used to compare the differences and a P-value<0.05 was considered to be statistically significant. In group A, Vitreous Chamber depth and optical axis elongated significantly, and refractive error shifted towards myopia during the observation period. In group B, Vitreous Chambers and optical axis elongated but the refractive power did not show significant changes. In group C, there was no significant elongation in Vitreous Chambers and optical axis, and the refractive power changed slightly towards hypermetropia. There were no significant changes in corneal refractive power in each group. Sustained near vision can promote Vitreous Chamber growth and induce myopic shifts in refractive power in adolescent monkeys. Our results demonstrate the potential for a primate model of near-work-related myopia.
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The effectiveness of progressive addition lenses on the progression of myopia in Chinese children
Ophthalmic and Physiological Optics, 2009Co-Authors: Zhikuan Yang, Weizhong Lan, Linxin Chen, Wen Liu, Jian Ge, Xiang Chen, Minbin YuAbstract:PURPOSE To evaluate the effectiveness of progressive addition lenses (PALs), with a near addition of +1.50 D, on the progression of myopia in Chinese children. METHODS We enrolled 178 Chinese juvenile-onset acquired myopes (aged 7-13 years, -0.50 to -3.00 D spherical refractive error), who did not have moderately or highly myopic parents, for a 2-year prospective study. They were randomly assigned to the PAL group or single vision (SV) group. Primary measurements, which included myopia progression and ocular biometry, were performed every 6 months. Treatment effect was adjusted for important covariates, by using a multiple linear regression model. RESULTS One hundred and forty-nine subjects (75 in SV and 74 in PAL) completed the 2-year study. The myopia progression (mean +/- S.D.) in the SV and PAL groups was -1.50 +/- 0.67 and -1.24 +/- 0.56 D, respectively. This difference of 0.26 D over 2 years was statistically significant (p = 0.01). The lens type (p = 0.02) and baseline spherical equivalent refraction (p = 0.05) were significant contributing factors to myopia progression. Mean increase in the depth of Vitreous Chamber was 0.70 +/- 0.40 and 0.59 +/- 0.24 mm, respectively. This difference of 0.11 mm was statistically significant (p = 0.04). Age (p < 0.01) was the only contributing factor to the elongation of Vitreous Chamber. Different near phoria (p < 0.01) and gender (p = 0.02) caused different treatment effects when wearing SV lenses. However, there were no factors found to influence the treatment effect of wearing PALs. CONCLUSIONS Compared with SV lenses, myopia progression was found to be retarded by PALs to some extent in Chinese children without moderately or highly myopic parents, especially for subjects with near esophoria or females.
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Influence of optical defocus and form deprivation on the emmetropization of infant rhesus monkeys
Annals of Eye Science, 2004Co-Authors: Junshu Wu, Juan Huang, Xingwu Zhong, Jian GeAbstract:PURPOSE: To investigate the influence of optical defocus and form deprivation on the emmetropization of infant rhesus monkeys. METHODS: Twenty-two normal infant rhesus monkeys, between 20 and 40 days of age, were divided into 2 groups of A (n=13) and B (n=9) by random. The monkeys from group A and B wore diffuser and -3.00 D spectacle lens over their right eyes. All the animals wore 0.00 D lens over their left eyes as control. The monkeys' refractive error, corneal topography, the depth of Vitreous Chamber were measured at the start of lens wear and at 2, 4, 6, 8, 12 weeks post-treatment. By these means, we can observe the changes of eye growth and refractive status dynamically. RESULTS: Among all the animals, there was no significant difference between the right and left eyes in Vitreous Chamber length at the start of lens wear (P > 0.05). During the course of observation, the Vitreous Chamber of all the animals elongated gradually. At 12 weeks post-treatment, the axial eyeball elongation of the treatment eyes of group A was more obvious than that of the control eyes (P 0.05). But we can still find the vitreou Chamber elongation of the treatment eyes was faster than that of the control eyes in this group. All the monkeys were hyperopic and there was no significant difference between their two eyes at the start of lens wear (P > 0.05). During the course of lens wear, all the eyes became less and less hyperopic. At 12 weeks post-treatment, the treatment eyes exhibited relative or absolute myopic status as compared with the fellow eyes both in group A and group B (P 0.05). CONCLUSIONS: Under the condition of optical defocus and form deprivation, the treated eyes exhibited relative or absolute myopic status mainly because of the faster growth of Vitreous Chamber. It implies that these two methods can intervene the process of emmetropization of infant rhesus monkeys.
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The study of photorefractive keratectomy induced defocus on emmetropization in infant monkeys
Chinese journal of ophthalmology, 2004Co-Authors: Xingwu Zhong, Jian Ge, Juan HuangAbstract:OBJECTIVE: To investigate the effect of photorefractive keratectomy (PRK) induced defocus on emmetropization in infant rhesus monkeys and to determine the role of visual feedback on emmetropization. METHODS: PRK was performed in 8 healthy rhesus monkeys age ranging from 2 to 3 months. Either 3.00 D of relative hyperopic or myopic defocus was produced in one eye and the fellow eye as controls. The eyes were examined periodically with corneal topography, cycloplegic retinoscopy, A-scan ultrasonography, and slit-lamp biomicroscopy. RESULTS: All operated eyes demonstrated re-epithelialization within 3 days post-surgically and maintained transparent. Compensating axial length growth occurred throughout the observation period. The rate of Vitreous Chamber elongation varied with the post-PRK refractive status of the eye. The hyperopia-induced eyes exhibited a Vitreous Chamber elongation faster than the fellow eyes (t = 3.656, P = 0.0354), whereas myopia-induced eyes demonstrated a Vitreous Chamber elongation slower than the fellow eyes (t = 3.576, P = 0.0374). CONCLUSIONS: PRK-induced-defocus altered axial growth rates and emmetropization in infant monkeys predictably. These results indicate that primate emmetropization is regulated by visual feedback and correction of refractive error on children should be careful. PRK-induced-defocus is a promising method for myopic animal model and for the investigation of vision science.
Alessandro Stocchino - One of the best experts on this subject based on the ideXlab platform.
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Investigation of the motion of a viscous fluid in the Vitreous cavity induced by eye rotations and implications for drug delivery.
Physics in Medicine and Biology, 2013Co-Authors: Andrea Bonfiglio, Rodolfo Repetto, Jennifer H Siggers, Alessandro StocchinoAbstract:Intravitreal drug delivery is a commonly used treatment for several retinal diseases. The objective of this research is to characterize and quantify the role of the Vitreous humor motion, induced by saccadic movements, on drug transport processes in the Vitreous Chamber. A Perspex model of the human Vitreous Chamber was created, and filled with a purely viscous fluid, representing eyes with a liquefied Vitreous humor or those containing viscous tamponade fluids. Periodic movements were applied to the model and the resulting three-dimensional (3D) flow fields were measured. Drug delivery within the Vitreous Chamber was investigated by calculating particle trajectories using integration over time of the experimental velocity fields. The motion of the Vitreous humor generated by saccadic eye movements is intrinsically 3D. Advective mass transport largely overcomes molecular diffusive transport and is significantly anisotropic, leading to a much faster drug dispersion than in the case of stationary Vitreous humor. Disregarding the effects of Vitreous humor motion due to eye movements when predicting the efficiency of drug delivery treatments leads to significant underestimation of the drug transport coefficients, and this, in turn, will lead to significantly erroneous predictions of the concentration levels on the retina.
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in vitro simulations of drug delivery in the Vitreous Chamber of the eye
ASME 2012 Summer Bioengineering Conference Parts A and B, 2012Co-Authors: Andrea Bonfiglio, Rodolfo Repetto, Alessandro Stocchino, Jennifer H SiggersAbstract:The Vitreous Chamber has an approximately spherical shape, and is filled with Vitreous humor, a transparent material with viscoelastic properties. The Vitreous humor has the mechanical roles of supporting the eye shape, promoting the adherence between the retina and the choroid, and acting as a barrier between the anterior and posterior segments of the eye for transport of heat and molecules [1]. Often, in elderly people, the Vitreous humor has almost Newtonian properties as a consequence of a liquefaction process consisting of degradation of the collagenous framework of the gel. Moreover, after vitrectomy the Vitreous humor is sometimes replaced with viscous tamponade fluids (typically silicone oils). Since intra-vitreal drug injection is increasingly used to treat retinal diseases, and the efficacy of this procedure depends on molecular transport processes after the injection, much of the biomechanical research on the Vitreous humor has focused on understanding transport processes in the Vitreous Chamber. Many authors have considered purely diffusive transport or alternatively diffusion with advective transport due to creeping bulk flow only [2,3]. However, when the Vitreous is liquefied, rotational motion of the eye has been shown to induce significant fluid flow, which plays a fundamental role for drug delivery in the Vitreous Chamber [4–7]. The most significant contribution to mass transport is due to the generation of a steady streaming flow, i.e. a steady flow resulting from the non-linearity in the equations. This flow component gives rise to a slow particle drift that becomes dominant over long times.Copyright © 2012 by ASME
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Barriers to transport induced by periodic oscillations in a physical model of the human Vitreous Chamber.
Physical review. E Statistical nonlinear and soft matter physics, 2011Co-Authors: Alberto Oliveri, Alessandro Stocchino, Marco StoraceAbstract:Understanding mixing processes that occur in the human Vitreous Chamber is of fundamental importance due to the relevant clinical implications in drug delivery treatments of several eye conditions. In this article we rely on experimental observations (which demonstrated that dispersion coefficients largely dominate diffusive coefficients) on a physical model of the human eye to perform an analysis based on Lagrangian trajectories. In particular, we study barriers to transport in a particularly significant two-dimensional section of the eye model by using nonlinear dynamical systems theoretical and numerical tools. Bifurcations in the system dynamics are investigated by varying the main physical parameters of the problem.
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barriers to transport induced by periodic oscillations in a physical model of the human Vitreous Chamber
Physical Review E, 2011Co-Authors: Alberto Oliveri, Alessandro Stocchino, Marco StoraceAbstract:Understanding mixing processes that occur in the human Vitreous Chamber is of fundamental importance due to the relevant clinical implications in drug delivery treatments of several eye conditions. In this article we rely on experimental observations (which demonstrated that dispersion coefficients largely dominate diffusive coefficients) on a physical model of the human eye to perform an analysis based on Lagrangian trajectories. In particular, we study barriers to transport in a particularly significant two-dimensional section of the eye model by using nonlinear dynamical systems theoretical and numerical tools. Bifurcations in the system dynamics are investigated by varying the main physical parameters of the problem. The posterior Chamber of the eye represents most of the volume of the human eye and is filled with Vitreous humor, an incompressible, transparent, and either viscoelastic or Newtonian fluid which accomplishes several mechanical and physiological tasks (1). The shape of the Vitreous Chamber is mostly spherical except for an indentation in the anterior part (due to the presence of the lens), whose size can be approximately 10%-30% of the eye globe mean radius. The human Vitreous can be set in motion by different kinds of eye rotations. The main eye movements occur with a vertical axis of rotation and are usually termed as saccades. The saccades are characterized by a wide range of amplitude and duration and have several physiological causes, for example, redirecting the line of sight. Metrics of saccadic eye movements are reported in detail in Ref. (2). In the same reference, measurements of the human eye movements are reported in different circumstances and in many cases saccadic movements possess a strong periodicity. Based on these observations, in the present analysis, saccades, as a first approximation, are reproduced with periodic sinusoidal tor- sional oscillations e(t) = A sin(ωt), where A is the oscillation amplitude and ω the angular frequency. A potentially important clinical implication of Vitreous humor dynamics is its effect on mass transport in the posterior Chamber. Indeed, several eye conditions (age-related macular degeneration, glaucoma, diabetic retinopathy) are treated by intravitreal delivery of drugs using different techniques (3) and, moreover, several drugs are effective only inside a narrow range of concentrations and for a prescribed length of time (4). Thus, an understanding of mixing processes in the Vitreous humor is extremely important to obtain the desired perfor- mances ofthe medical treatment. Inthe literaturemany studies (theoretical and numerical) are reported regarding exclusively diffusive transport in the Vitreous humor (see Ref. (5 )f or a comprehensive bibliography), disregarding completely the role of the Vitreous motion due to saccades. On the contrary, the dynamical processes that the Vitreous undergoes during
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mixing processes in the Vitreous Chamber induced by eye rotations
Physics in Medicine and Biology, 2010Co-Authors: Alessandro Stocchino, Rodolfo Repetto, Jennifer H SiggersAbstract:In this paper, we study a model of flow in the Vitreous humour in the posterior Chamber of the human eye, induced by saccadic eye rotations. We concentrate on the effect of the shape of the Chamber upon the mixing properties of the induced flows. We make particle image velocimetry measurements of the fluid velocity in a transparent plastic (Perspex) model of the posterior Chamber during sinusoidal torsional oscillations about a vertical axis. We use a Newtonian fluid to model the Vitreous humour, which is most realistic when either the Vitreous humour is liquefied or has been replaced by purely viscous tamponade fluids. The model of the posterior Chamber is a sphere with an indentation, representing the effect of the lens. In spite of the purely periodic forcing, a steady streaming flow is generated, which plays a fundamental role in the mixing processes in the domain. The streaming flow differs markedly from that in a perfect sphere, and its topological characteristics change substantially as the frequency of oscillation varies. We discuss the flow characteristics in detail and show that, for physiological parameter values, the Peclet number (based on a suitable measure of the steady streaming velocity) is large, suggesting that advection strongly dominates over diffusion for mass transport phenomena. We also compute particle trajectories based on the streaming velocity and use these to investigate the stirring properties of the flow.
E. Colangeli - One of the best experts on this subject based on the ideXlab platform.
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Traction on the retina induced by saccadic eye movements in the presence of posterior Vitreous detachment
Biomechanics and Modeling in Mechanobiology, 2011Co-Authors: R. Repetto, A. Tatone, A. Testa, E. ColangeliAbstract:Posterior Vitreous detachment is a fairly common condition in elderly people. Tractions exerted by the detached Vitreous on the retina may result in retinal tears and detachments. We studied how these tractions can arise from saccadic eye movements. Numerical simulations have been performed on a two-dimensional model of the Vitreous Chamber within a rigid spherical sclera, subjected to prescribed finite-amplitude rotations about a vertical axis. The Vitreous Chamber was assumed to be split into two regions: one occupied by the detached Vitreous, modeled as an elastic viscous solid, and the other occupied by the separated liquefied Vitreous, modeled as a Newtonian fluid. At the interface between the two phases, we also considered the presence of the Vitreous cortex, modeled as an elastic membrane. We tested several different configurations of the interface. In all cases, we found that eye rotations generate large tractions on the retina close to the attachment points of the membrane. Comparing them, we identified configurations of the Vitreous detachment that exhibit higher tractions. We also investigated how the response to saccadic movements depends on some physical parameters, in particular on the rheological properties of the solid phase and the membrane. The numerical simulations show that the generated tractions may be of the same order of magnitude as the adhesive force between the retina and the pigment epithelium. Therefore, the model provides a sound physical justification for the hypothesis that saccadic movements, in the presence of posterior Vitreous detachment, could be responsible for high tractions on the retina, which may trigger retinal tear formation.
