Advisor(s)

George G. Adams

Contributor(s)

Kai-Tak Wan, Jeffrey W. Ruberti

Date of Award

2009

Date Accepted

8-2009

Degree Grantor

Northeastern University

Degree Level

M.S.

Degree Name

Master of Science

Department or Academic Unit

College of Engineering. Department of Mechanical and Industrial Engineering.

Keywords

biomechanics, Choroid, Finite element, Macular degeneration, Retina

Subject Categories

Axial myopia

Disciplines

Mechanical Engineering

Abstract

Axial myopia is characterized by an elongation of the eye and defocusing of the image formed on the macula (central retina). The elongation in high myopia stretches the retina, which can cause hemorrhage, atrophy and the formation of new blood vessels in the macula and underlying tissue. This process leads to scarring, blurring and even loss of useful central vision.

A modeling approach has been developed to study the effect of deformed geometry, material properties and intraocular pressure on the pathology of myopic macular degeneration. 2-D axisymmetric and three dimensional finite element models of a myopic eye were generated to study the induced stress and integrity of the retinal layers. Cases of linear, bilinear and hyper-elastic Mooney-Rivlin material behavior were examined for the retina and linear and hyper-elastic Ogden (n=1) material model for the choroid. Mechanical tests were performed to mechanical material properties of bovine choroid membrane along with a traditional uniaxial tensile test. The modulus of elasticity for the bovine choroid averaged 0.2 ± 0.08 MPa. Direct measurements enable the use of more realistic material properties during modeling. The finite element models showed maximum radial and circumferential stress in the region of the macula in each model. Maximum radial and circumferential tensile strains of 11% were observed in the macular region. Such high strains indicate that this region would be most vulnerable to mechanical changes occurring in axial myopia. Increased tensile strain (stretching of the retina) could lead to reduction of the density of photoreceptor cells, hemorrhage and formation of cracks in the macular region making it favorable for new blood vessels to grow in this region. Formation of these vessels can lead to bleeding; the result of which is scarring and loss of vision.

Thus the finite element modeling proves to be an effective method to study the mechanics involved in axial myopia, providing a mechanical explanation for the pathology of myopic macular degeneration.

Document Type

Master's Thesis

Rights Holder

Aneesh Ajay Bendre


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