Glaucoma and the brain
Glaucomatous neuropathy extends throughout the visual system
Glaucomatous neuropathy is not limited to retinal ganglion cells but also extends throughout the visual system. Modern neuroimaging techniques can provide a useful tool to evaluate the disease in humans in vivo, said Carlo Nucci MD, PhD, Full Professor of Ophthalmology at University of Rome Tor Vergata, Italy.
In a series of studies he and his associates have conducted, neuroimaging with diffusion tensor magnetic resonance imaging (MRI) showed that, in the optic nerve and optic nerve radiations, glaucomatous visual field loss was associated with a progressive increase in mean diffusivity and a progressive decrease in fractional anisotropy, both of which are biomarkers of axonal damage, he told the 13th European Glaucoma Society Congress in Florence, Italy.
They also observed that in patients with early glaucoma the damage to the optic nerve was predominantly located at the proximal retrobulbar region, whereas in patients with advanced glaucoma, the optic nerve’s distal end was also damaged.
More recently they have conducted a study using the newer, diffusion kurtosis MRI. They found that the damage in glaucoma reached into white matter tracts, which are involved in the processing and integrating of visual information in the brain.
Dr Nucci noted that there is also evidence that in glaucoma there is damage to the magnocellular layer of the lateral geniculate nucleus, which is important in fixation and maintaining a stable image during saccadic eye movements. In a study evaluating patients’ eye movements during reading, using a text-imprinted microperimeter screen and a high-frequency eye tracker, his team observed that patients with glaucoma had very specific alterations in their eye movement.
GLAUCOMA AND ALZHEIMER’S DISEASE
In most patients, the intraocular pressure (IOP)-related death of retinal ganglion cells is the most likely initiating pathogenic mechanism for the more pervasive features of glaucomatous neurodegeneration, Dr Nucci said. However, the presence of a pre-existing neurodegenerative process might also render these cells more susceptible to local stress factors, he noted.
There are several links between glaucoma and other neurodegenerative diseases including Alzheimer’s disease, he added. In a recent study, he and his associates found that patients with Alzheimer’s disease had a five-times higher frequency than controls of glaucoma-like alterations in both the retinal nerve fibre layer, as detected by Heidelberg retinal tomography, and the visual field, as measured with frequency-doubling technology. Furthermore, there was no link between the damage and IOP levels.
Carlo Nucci: firstname.lastname@example.org