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 Corneal Surgery Dental applications 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. Biological materials such as a human cornea is made up mostly of water. Vision is dependent on the hydration of the cornea. Vision is dependent on the hydration of the cornea. Important to understand how it remains hydrated. 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. 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? What causes the viscous flows in the cornea? Is gravity a driving force? Is gravity a driving force?

What is a Cornea? The Outermost layer of the eye. The Outermost layer of the eye. Consists of three layers: Consists of three layers: The epithelial membrane (outer most layer) The epithelial membrane (outer most layer) The stroma (makes up 90% of cornea) The stroma (makes up 90% of cornea) The endothelial membrane The endothelial membrane Figure 2. Extracted Human Cornea being held by a suction device used in LASIK eye surgery. Figure 1. Anatomy of Eye

Current Corneal Research Corneal Refractive Surgery Corneal Refractive Surgery LASIK- LASIK- Laser-Assisted In Situ Keratomileusis Most popular refractive surgery in America. 1.3 million American’s had LASIK in 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 Intrastromal Corrective Sugery Near IR light, which is retinal safe, is focused under the corneal surface in the stroma. 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. Lenticle is ablated without the creation of a flap.

Current Corneal Research Corneal Replacement Surgery 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. Modeled the Cornea in Gambit as 2 Dimensional Plane wall and Curved Surface. Geometries and Boundary Conditions 0.5 mm 12 mm T amb = 308KT s =310K 0.5 mm 12 mm Tamb= 308KTs=310K

Cornea as a Flat Plane Wall Gravity is driving the free convective flows in the cornea. Gravity is driving the free convective flows in the cornea. Without gravity as an operating condition in Fluent there was no velocity. 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. Free convective flows within the cornea. Buoyancy is the driving force for these flows Buoyancy is the driving force for these flows Without gravity there was no velocity Without gravity there was no velocity The flows in the cornea maintain hydration of the cornea which is necessary for vision. The flows in the cornea maintain hydration of the cornea which is necessary for vision.

References: Kumar S, Acharya S, Beuerman R, Palkama A Numerical Solution of Ocular Fluid Dynamics in a Rabbit Eye: Parametric Effects. Annals of Biomedical Engineering. 3493): Li LY, Tighe BJ, Ruberti JW Mathematical Modelling of Corneal Swelling. Biomechanical Model Mechanobiology. 3: Ridouane EH, Campo A 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

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