Download Viscous Flows in the Human Cornea

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:


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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
12 mm
Ts=310K
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:
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
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: 114123
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?