Viscous Flows in Viscous Flows in the Human the Human

CorneaCorneaBy: Molly FaheyBy: Molly Fahey

Viscous Flows, Fall 2006Viscous Flows, Fall 2006

December 12, 2006December 12, 2006

Background Background Information/Previous ResearchInformation/Previous Research

Ultra-short pulsed lasers for Ultra-short pulsed lasers for biomedical applications biomedical applications

Corneal SurgeryCorneal Surgery Dental applicationsDental applications

Laser Used for Research (FDA)Laser Used for Research (FDA)--Raydiance Desktop LaserRaydiance Desktop Laser-Wavelength = 1,550 nm-Wavelength = 1,550 nm-Pulse Duration ≈ 1 ps-Pulse Duration ≈ 1 ps

Purpose: Correlation between Purpose: Correlation between Viscous Flows and Laser Viscous Flows and Laser

Ablation ResearchAblation Research Biological materials such as a human cornea Biological materials such as a human cornea

is made up mostly of water. is made up mostly of water. Vision is dependent on the hydration of the Vision is dependent on the hydration of the

cornea. cornea. Important to understand how it remains hydrated.Important to understand how it remains hydrated.

In order to improve on current or develop In order to improve on current or develop novel corneal surgery techniques one must novel corneal surgery techniques one must fully understand the mechanics of the eye. 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?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 ResearchCurrent Corneal Research Corneal Refractive SurgeryCorneal Refractive Surgery

LASIK-LASIK-

Laser-Assisted In SituLaser-Assisted In Situ KeratomileusisKeratomileusis

•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 ResearchCurrent Corneal Research

Intrastromal Corrective SugeryIntrastromal Corrective Sugery Near IR light, which is retinal safe, is focused Near IR light, which is retinal safe, is focused

under the corneal surface in the stroma.under the corneal surface in the stroma. Lenticle is ablated without the creation of a Lenticle is ablated without the creation of a

flap.flap.

Current Corneal ResearchCurrent Corneal Research

Corneal Replacement SurgeryCorneal Replacement Surgery

Using Fluent /Gambit to Using Fluent /Gambit to determine the nature of the determine the nature of the

viscous flows within the viscous flows within the cornea.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 Conditions0.5 mm

12 mm

Tamb= 308K Ts=310K

0.5 mm

12 mm

Tamb= 308K

Ts=310K

Cornea as a Flat Plane WallCornea 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 Velocity Vectors in the Center Region of the Cornea.Region of the Cornea.

Velocity Vectors: Curved Velocity Vectors: Curved GeometryGeometry

Velocity vector: Center region Velocity vector: Center region of curved Geometryof curved Geometry

Velocity Vector: Top Region of Velocity Vector: Top Region of Curved GeometryCurved Geometry

Pressure ContoursPressure Contours

Flat Geometry Curved Geometry

Temperature ContoursTemperature Contours

Flat Geometry Curved Geometry

Conclusion:Conclusion:

Free convective flows within the Free convective flows within the cornea. cornea.

Buoyancy is the driving force for Buoyancy is the driving force for these flowsthese flows Without gravity there was no velocityWithout gravity there was no velocity

The flows in the cornea maintain The flows in the cornea maintain hydration of the cornea which is hydration of the cornea which is necessary for vision.necessary for vision.

References:References:

Kumar S, Acharya S, Beuerman R, Palkama A. 2005. Kumar S, Acharya S, Beuerman R, Palkama A. 2005. Numerical Solution of Ocular Fluid Dynamics in a Numerical Solution of Ocular Fluid Dynamics in a Rabbit Eye: Parametric Effects. Annals of Rabbit Eye: Parametric Effects. Annals of Biomedical Engineering. 3493): 530-544Biomedical Engineering. 3493): 530-544

Li LY, Tighe BJ, Ruberti JW. 2004. Mathematical Li LY, Tighe BJ, Ruberti JW. 2004. Mathematical Modelling of Corneal Swelling. Biomechanical Modelling of Corneal Swelling. Biomechanical Model Mechanobiology. 3: 114-123Model Mechanobiology. 3: 114-123

Ridouane EH, Campo A. 2005. Model for the Heat Ridouane EH, Campo A. 2005. Model for the Heat Transmission in the Human Eye. Proceedings of Transmission in the Human Eye. Proceedings of the 2005 International Mechanical Engineering the 2005 International Mechanical Engineering Congress and Exposition; 2005 November 5-11; Congress and Exposition; 2005 November 5-11; Orlando, Florida, USA: ASME. p 535-539.Orlando, Florida, USA: ASME. p 535-539.

Questions?Questions?