Viscous Flows in the Human Cornea by jizhen1947


									Viscous Flows in the
  Human Cornea
        By: Molly Fahey
    Viscous Flows, Fall 2006
      December 12, 2006
 Background Information/Previous
Ultra-short pulsed lasers for biomedical
    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
            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
    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
Velocity Vector: Top Region of Curved
       Pressure Contours
Flat Geometry        Curved Geometry
      Temperature Contours
Flat Geometry      Curved Geometry

   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.

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-
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.

To top