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Wu, H. T. D., Donaldson, P. J., & Vaghefi, E. (2016). Modelling of lens fluid dynamics with additions of different geometrical structures. In Investigative Ophthalmology & Visual Science Vol. 57 (pp. 1 page). Seattle, WA: Association for Research in Vision and Ophthalmology.
http://iovs.arvojournals.org/article.aspx?articleid=2563764
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ARVO 2016 Annual Meeting Abstracts
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505 Lens physiology
Thursday, May 05, 2016 8:00 AM–9:45 AM Exhibit/Poster Hall Poster Session
Program #/Board # Range: 5735–5743/A0163–A0171 Organizing Section: Lens
Program Number: 5735 Poster Board Number: A0163 Presentation Time: 8:00 AM–9:45 AM
Age-Dependency of Diffusion within the Human Lens Capsule Vivian M. Sueiras1, Vincent Moy2, Noel M. Ziebarth1. 1Biomedical Engineering, College of Engineering, University of Miami, Coral Gables, FL; 2Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL.
Purpose: To determine if diffusion within the human lens capsule changes as a function of age.
Methods: Whole lenses from 7 human cadavers (age: 21-61 years) were retrieved from the Florida Lions Eye Bank. When the technicians harvested donor corneas suitable for transplantation, they also removed the lenses for use for this project. The human lenses arrived from the eye bank in sealed vials filled with Dulbecco’s modified eagle medium placed in Styrofoam containers filled with ice. The whole lenses were stored in the refrigerator at 4°C before they were used. The anterior lens capsule was separated from the lens using the continuous curvilinear capsulorhexis technique. Each excised capsule was submerged in a 0.01% solution of anionic, fluorescein-labeled dextran in PBS (500kD MW). The samples were soaked overnight, allowing the molecules to diffuse into the capsule and to reach chemical and diffusional equilibrium. The capsules were then removed from the bath, washed 2 times with PBS, plated on a glass bottom dish, and hydrated with PBS. Fluorescence recovery after photobleaching (FRAP) experiments using a Nikon A1R confocal microscope were conducted on the lens capsules to quantify diffusion. The argon laser was used to bleach out a circle of radius 10μm at a plane within the capsule, creating a region of interest (ROI). Changes in fluorescence intensity stemming from the diffusion of the fluorescent tracer were monitored over time for 120 seconds.
This data was normalized using an “unbleached” region away from the ROI. The time to half recovery was determined for each sample.
Results: The time to half maximum recovery ranged from 6.24 to 7.85s. Prior to 40 years of age, the half maximum recovery time was constant and averaged 6.29 ± 0.06s. After 40 years of age, the recovery time linearly increased, indicating that transport was impeded in older lenses.
Conclusions: With age, the rate of transport of dextran within the lens capsule significantly slows. These results could indicate that the diffusion of molecules relevant to lens biology is also impeded in older lens capsules.
Commercial Relationships: Vivian M. Sueiras, None;
Vincent Moy, None; Noel M. Ziebarth, None
Support: James & Esther King Biomedical Research Program Shared Instrument Grant (#24157)
Program Number: 5736 Poster Board Number: A0164 Presentation Time: 8:00 AM–9:45 AM
Modelling of lens fluid dynamics with additions of different geometrical structures
Ho Ting Duncan Wu1, Paul J. Donaldson2, Ehsan Vaghefi1.
1Optometry, University of Auckland, Auckland, New Zealand;
2Physiology, University of Auckland, Auckland, New Zealand.
Purpose: Vaghefi produced a 3D computer model of the lens capable to accurately predict its fluid dynamics [1]. However, the geometric domain of this model was not anatomically accurate. We aim to examine the effects geometrical structures such as sutures or the
anterior/ posterior chambers of the eye have on the fluid dynamics of the lens and its surroundings.
Methods: The 3D model of the lens developed by Vaghefi using CMISS has been redeveloped using COMSOL. Initially, we created models which included the 3D Y-sutures and also the anterior and posterior chambers of the eye. The complex geometric domain has then been discretised into 97142 elements capable of capturing key information. Next, the governing equations and appropriate boundary conditions of the lens under normal condition were applied and invoked (detailed in Vaghefi et al. [1]). Finally, the fluid dynamics of the lens, including its water content gradient was solved for.
Results: The model was able to predict values and pattern of fluid velocity, pressure, as well as intracellular and extracellular solutes concentration. The fluid appeared to flow from the anterior and posterior chambers respectively to the core of the lens and flows outward around the equatorial region. The velocity appeared to be the highest in the posterior outer cortex and the lowest at the inner anterior cortex. Radially from surface to core, [Na]iranges from 5.78 to 9.99 mM, [Na]e from 103.44 to 112.65 mM, [Cl]i from 9.80 to 10.48 mM and [Cl]e from 113.94 to 115.43 mM. The intracellular concentrations were highest in the core and lowest in the outer cortex, whilst the extracellular concentrations were reversed. These results are consistent with predictions by Vaghefi’s model.
Conclusions: 3D Y-sutures and anterior/ posterior chambers of the eye were added to a redeveloped fluid dynamics model of the lens.
Pattern and values of fluid velocity as well as solutes concentration matches well with predictions from Vaghefi’s model suggesting these geometrical structures have no significant effects on its fluid dynamics. We are now able to build on top of this modelling framework, and be able to calculate water gradient of the lens, which creates its refractive index gradient. This enables us to create links between physiological changes of the lens to its overarching optical performance, through the lenticular fluid dynamics.
[1] E. Vaghefi et al. Biomed.Eng.Online, vol. 11(1), p.1,2012 Commercial Relationships: Ho Ting Duncan Wu, None;
Paul J. Donaldson, None; Ehsan Vaghefi, None
Support: Health Research Council Emerging Scientist First Award Program Number: 5737 Poster Board Number: A0165
Presentation Time: 8:00 AM–9:45 AM
Functions of the lipid bilayer portion of the fiber cell plasma membranes in the maintaining lens homeostasis
Witold K. Subczynski2, Laxman Mainali3, Marija Raguz4,
William J. O’Brien1. 1Opthalmology, Medical College on Wisconsin, Milwaukee, WI; 2Biophysics, Medical College of Wisconsin, Milwaukee, WI; 3Biophysics, Medical College of Wisconsin, Milwaukee, WI; 4Biophysics and Medical Physics, University of Split, Split, Croatia.
Purpose: The plasma membrane together with the cytoskeleton forms the only supramolecular structure of the matured fiber cell which accounts for mostly all fiber cell lipids. We will focus on the organization and properties of the lipid bilayer portion of the fiber cell membrane and discuss the significant functions which this lipid bilayer plays in maintaining homeostasis of the fiber-cell plasma membrane, the fiber cell itself, and the whole lens.
Methods: Results presented here were obtained using EPR spin labeling methods and differential scanning calorimetry. Intact fiber cell plasma membranes from cortical and nuclear regions of human lenses as well as lens lipid membranes (made of the total lipid extracts from intact membranes) were investigated.
Results: (1) The extremely high (saturating) content of cholesterol (Chol) in the fiber-cell membrane keeps the bulk physical properties of the lipid-bilayer portion of the membrane consistent
