Viscous Flows in the Human Cornea by jizhen1947

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									Viscous Flows in the
  Human Cornea
        By: Molly Fahey
    Viscous Flows, Fall 2006
      December 12, 2006
 Background Information/Previous
            Research
Ultra-short pulsed lasers for biomedical
applications
    Corneal Surgery
    Dental applications



Laser Used for Research (FDA)
 -Raydiance Desktop Laser
  -Wavelength = 1,550 nm
  -Pulse Duration ≈ 1 ps
    Purpose: Correlation between Viscous
     Flows and Laser Ablation Research
   Biological materials such as a human cornea is made up
    mostly of water.
   Vision is dependent on the hydration of the cornea.
       Important to understand how it remains hydrated.
   In order to improve on current or develop novel
    corneal surgery techniques one must fully understand
    the mechanics of the eye.
       What causes the viscous flows in the cornea?
       Is gravity a driving force?
                        What is a Cornea?

   The Outermost layer of the eye.
   Consists of three layers:
       The epithelial membrane (outer most layer)
       The stroma (makes up 90% of cornea)
       The endothelial membrane


                                                          Figure 1. Anatomy of Eye




                                           Figure 2.
                                           Extracted Human Cornea being held by a
                                           suction device used in LASIK eye surgery.
              Current Corneal Research
   Corneal Refractive Surgery
       LASIK-
    Laser-Assisted In Situ Keratomileusis


                                    •Most popular refractive surgery in America.
                                    •1.3 million American’s had LASIK in 2005.
                                    •A flap is made with a mechanical blade.
                                    •An excimer laser (ultraviolet light) is used to
                                    ablate lenticle in the corneal stroma to correct
                                    vision.
            Current Corneal Research

   Intrastromal Corrective Sugery
     Near IR light, which is retinal safe, is focused under
      the corneal surface in the stroma.
     Lenticle is ablated without the creation of a flap.
          Current Corneal Research

   Corneal Replacement Surgery
    Using Fluent /Gambit to determine the
     nature of the viscous flows within the
                     cornea.
    Modeled the Cornea in Gambit as 2 Dimensional Plane wall and Curved Surface.
                      Geometries and Boundary Conditions
                                                   0.5 mm
                 0.5 mm




    Tamb= 308K            Ts=310K                             12 mm



        12 mm
                                    Tamb= 308K                Ts=310K
              Cornea as a Flat Plane Wall
   Gravity is driving the free convective flows in the cornea.
           Without gravity as an operating condition in Fluent there was no velocity.
                                Velocity Vectors:
                               Top Half of the cornea
Velocity Vectors in the Center Region of
              the Cornea.
Velocity Vectors: Curved Geometry
Velocity vector: Center region of curved
               Geometry
Velocity Vector: Top Region of Curved
              Geometry
       Pressure Contours
Flat Geometry        Curved Geometry
      Temperature Contours
Flat Geometry      Curved Geometry
                       Conclusion:

   Free convective flows within the cornea.
   Buoyancy is the driving force for these flows
       Without gravity there was no velocity
   The flows in the cornea maintain hydration of
    the cornea which is necessary for vision.
                       References:

Kumar S, Acharya S, Beuerman R, Palkama A. 2005. Numerical
   Solution of Ocular Fluid Dynamics in a Rabbit Eye: Parametric
   Effects. Annals of Biomedical Engineering. 3493): 530-544
Li LY, Tighe BJ, Ruberti JW. 2004. Mathematical Modelling of
   Corneal Swelling. Biomechanical Model Mechanobiology. 3: 114-
   123
Ridouane EH, Campo A. 2005. Model for the Heat Transmission in
   the Human Eye. Proceedings of the 2005 International
   Mechanical Engineering Congress and Exposition; 2005
   November 5-11; Orlando, Florida, USA: ASME. p 535-539.
Questions?

								
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