This study examined how different shapes of Bruch's membrane openings (BMOs) in rats affect biomechanics and could influence glaucoma. Histology slides of 8 rat eyes were used to create 3D models of each BMO shape. Finite element analysis showed irregularly shaped BMOs experienced up to 30% higher peak strain than regular shapes when subjected to simulated eye pressure. This suggests BMO shape may be an important factor in glaucoma susceptibility for rats and irregular openings could increase vulnerability to damage from elevated intraocular pressure.

1. Modeling the Effects of Bruch’s Membrane Opening Shape on the Biomechanics of the
Rat Model of Glaucoma
Nicole Gullatt1,2, Stephen Schwaner2, Eric Snider2, C. Ross Ethier2
1
Benjamin E. Mays High School, 2
Wallace H. Coulter Department of Biomedical Engineering,
Georgia Institute of Technology and Emory University
Introduction: Glaucoma is a disease of complex pathophysiology and is the second leading
cause of blindness. Blindness in glaucoma is due to the death of retinal ganglion cells (RGCs),
the cells that transmit visual information to the brain. A well-established risk factor for this
group of eye diseases is elevated intra-ocular pressure (IOP). Increased IOP causes
mechanical stress and strain in optic nerve head (ONH) tissues, leading to RGC death.
However, this process is not well understood. Therefore, the development of novel treatments
for glaucoma will require a better understanding of how complex ONH biomechanics drive the
process of RGC death. To accomplish this, we must first understand ONH biomechanics in
animal models of glaucoma, including the rat, a well-accepted and widely used model. To
contribute to this understanding, we examined Bruch’s membrane (BM), a key structure
through which RGC axons pass through as they exit the eye. Specifically, we modeled the
effects that different rat BM opening shapes have on the stress and strain experienced by
RGC axons, to determine if irregular BM opening shapes could potentially increase RGC
susceptibility to elevated IOP in the rat model of glaucoma.
Materials and Methods: Histology slides from eight rat eyes were manually delineated to
produce point clouds describing each Bruch’s membrane opening (BMO) shape using a
computer program called Multiview. A CAD model of each BMO shape was created by cutting
each BMO shape out of a digital, circular membrane of 10 µm radius and 1 µm thickness using
the program Rhino. Abaqus, finite element modeling software, was used to apply a mesh to
each model and simulate stress and strain around each BMO under biaxial loading conditions
Results and Discussion: Irregular BMO shapes experienced higher 95th percentile first
principal strain values than more regularly shaped openings. Differences in 95th percentile
strain of up to 30% were predicted between models.
Conclusions: The simulated strain values indicate that BMO shape could be an important
factor in the rat model of glaucoma and that a more irregular BMO shape could potentially
increase susceptibility to IOP-related damage in glaucoma.