NIH funds IU optometrists using new innovations to improve glaucoma treatment
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BLOOMINGTON, Ind. -- Two Indiana University professors of optometry will use a $1.4 million grant from the National Institutes of Health to advance innovations made in their respective labs toward overcoming longstanding barriers to the development of new treatments for glaucoma, the second-leading cause of permanent blindness in the world.
IU School of Optometry professor William H. Swanson will lead a collaboration with professor Stephen A. Burns that takes advances in neural modeling and visual psychophysics made in Swanson’s lab and improvements in the diagnostic imaging of the retina made in Burns’ lab to develop better methods for diagnosing and assessing the progression of glaucoma.
The team thinks it can better understand the processes by which aging and disease affect the retinal nerve fiber layer -- the layers of nerve fibers of the retina in the back of the eye that become the optic nerve -- by using high-resolution-imaging data to measure ganglion cell loss through the analysis of 3-D images of the fiber layer. Glaucoma is a disease of the eye in which sensitivity to ocular pressure causes damage to the retina and optic nerve, which are components of the central nervous system and do not regenerate.
Ganglion cells are neurons near the inner surface of the retina that collect and transfer visual information from the eye to the brain. Current measures for the effects of ganglion cell death have been based on the thickness of the retinal never fiber layer, rather than the entire structure of the layer.
But retinal ganglion cell numbers, and subsequently fiber layer thickness, can vary as much as two-fold among any given age group of healthy people, Swanson noted, so a person who starts at the high end of the normal range could lose half of their cells and still be at the lower limit of normal.
“That makes it difficult to detect early stages of the disease from what is often seen as normal variability in healthy people,” he said. “What we are doing that is new is measuring the entire structure of the retinal nerve fiber layer, which is less variable from subject to subject.”
Glaucoma is often thought to initially cause a loss of peripheral vision, which doctors measure with perimetry, a measurement of visual sensitivity determined at a number of locations across the visual field. But if these locations are not where damage has occurred then the damage goes undiscovered, Swanson said.
“Our goal is that the doctor will be able to take a picture of the back of the eye showing where the retinal nerve fiber layer structure is abnormal. That image could then be used to guide the doctor to test corresponding locations with perimetry,” Swanson said.
Measuring the microstructure of the retinal nerve fiber layer has become possible through development by the Burns lab of a wide-field adaptive optics scanning laser ophthalmoscope that allows for high-resolution imaging of the layer while also overcoming imaging barriers in aging eyes.
Swanson’s lab over the same time has developed a new form of perimetry that reduces between-subject variability in people free of glaucoma and in-subject variability in glaucoma patients. Together, the two teams will use Burns’ custom-designed ophthalmoscope along with spectral domain ocular coherence tomography to perform high-resolution imaging of the retinal layer. Spectral domain ocular coherence tomography is typically used to measure layer thickness, but a special agreement with Heidelberg Engineering will allow Swanson and Burns to customize and export raw data that traditionally would have had limited applications for their research.
“Our first step is to reduce spurious features produced in image acquisition by using a custom 3-D segmentation process,” Swanson said. “The second step will be to produce images that encode angle and density of fibers by using steerable spatial filters to identify individual nerve fibers.”
These new images, in the future, could then be used by doctors to conduct more precise testing through better detection of damaged areas.
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