The Effects of Femtosecond Laser Created Drainage Channels on the Aqueous Humor Outflow Dynamics of the Eye.

Various treatments have been introduced to delay or slow the progress of glaucoma, one of the leading causes of blindness, by reducing intraocular pressure (IOP), the unique manageable factor in glaucoma. However, there are limitations to the continuous usage of currently available treatments. A femtosecond laser presents the potential of advanced treatment by significantly reducing damage to tissues. This dissertation will address the compressive aspects of glaucoma and its treatments and the development of a minimally invasive surgical procedure and a supporting tool to improve the efficiency of this procedure. The experimental setup was built to scan the eye with a femtosecond laser in a predetermined pattern with adjustable parameters. The outflow rate was measured before and after the laser treatment to evaluate the effect of the channel. It was demonstrated that the subsurface scleral channel that increases aqueous humor (AH) outflow rate can be created in ex vivo rabbit eyes with a femtosecond laser. Considering that the goal of glaucoma treatment is to reduce IOP into the normal range, a tool is required to predict the channel dimensions to achieve a predetermined IOP reduction. I developed a 3D finite element model and demonstrated its potential as a tool for estimating channel dimensions by fitting the experimental data to the model. The experimental setup was altered to make a scan on an in vivo rabbit. It was demonstrated that the subsurface scleral channel can be created in the eyes of in vivo rabbits and IOP can be reduced with this channel. It was found that IOP can be reduced with a positive relation to the dimensions of the channel, demonstrating the potential for controlled IOP reduction by manipulating channel dimensions. Therefore, it can be concluded that the subsurface scleral AH drainage channel can be created with a femtosecond laser, overcoming the disadvantages of current treatments. The method has the potential of controlling IOP reduction with the channel dimensions. 3D FEM has potential as a tool for predicting the post treatment IOP and calculating channel dimensions for a required IOP reduction.Ph.D.Biomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61628/1/dchai_1.pd

Measurement of Corneal Elasticity with an Acoustic Radiation Force Elasticity Microscope

To investigate the role of collagen structure in corneal biomechanics, measurement of localized corneal elasticity with minimal destruction to the tissue is necessary. We adopted the recently developed acoustic radiation force elastic microscopy (ARFEM) technique to measure localize biomechanical properties of the human cornea. In ARFEM, a low-frequency, high-intensity acoustic force is used to displace a femtosecond laser-generated microbubble, while high-frequency, low-intensity ultrasound is used to monitor the position of the microbubble within the cornea. Two ex vivo human corneas from a single donor were dehydrated to physiologic thickness, embedded in gelatin and then evaluated using the ARFEM technique. In the direction perpendicular to the corneal surface, ARFEM measurements provided elasticity values of E = 1.39 ± 0.28 kPa for the central anterior cornea and E = 0.71 ± 0.21 kPa for the central posterior cornea in pilot studies. The increased value of corneal elasticity in the anterior cornea correlates with the higher density of interweaving lamellae in this region

Custom built nonlinear optical crosslinking (NLO CXL) device capable of producing mechanical stiffening in ex vivo rabbit corneas.

The purpose of this study was to develop and test a nonlinear optical device to photoactivate riboflavin to produce spatially controlled collagen crosslinking and mechanical stiffening within the cornea. A nonlinear optical device using a variable numerical aperture objective was built and coupled to a Chameleon femtosecond laser. Ex vivo rabbit eyes were then saturated with riboflavin and scanned with various scanning parameters over a 4 mm area in the central cornea. Effectiveness of NLO CXL was assessed by evaluating corneal collagen auto fluorescence (CAF). To determine mechanical stiffening effects, corneas were removed from the eye and subjected to indentation testing using a 1 mm diameter probe and force transducer. NLO CXL was also compared to standard UVA CXL. The NLO CXL delivery device was able to induce a significant increase in corneal stiffness, comparable to the increase produced by standard UVA CXL

IMECE2005-81651 TOLERANCE ANALYSIS CONSIDERING WELD DISTORTION BY USE OF PREGENERATED DATABASE

ABSTRACT A general and efficient methodology has been developed to analyze dimensional variations of an assembly, taking into account of the weld distortion. Weld distortion is generally probabilistic because of the random nature of welding parameters such as the welding speed, maximum welding temperature, ambient temperature, etc. The methodology is illustrated by a very simple example of two perpendicular plates fillet-welded to each other. Two steps comprise the methodology: establishment of a weld-distortion database, and tolerance analysis using the database. To establish the database, thermo-elasto-plastic finite element analyses are conducted to compute the weld distortion for all combinations of discrete values of major welding parameters. In the second step of tolerance analysis, the weld distortion retrieved from the database is used in addition to the dimensional tolerances of the parts. As a result of such an analysis, sensitivities of the assembly's dimensional variations to the part tolerances and weld distortion are obtained, which can be help improve the dimensional quality of the assembly

Nonlinear Optical Macroscopic Assessment of 3-D Corneal Collagen Organization and Axial Biomechanics

Collagen fibers in the anterior cornea are highly intertwined, unlike those in the posterior cornea. This axial gradient corresponds to a decrease in elastic modulus, suggesting that specific fiber organization controls corneal biomechanics and shape