New research shows that the brain—not the eye—controls the cellular process that leads to glaucoma. The results may not only spur treatments for glaucoma, but also help develop future therapies for preserving brain function in other age-related disorders, such as Alzheimer’s.
glaucoma, loss of the visual field in each eye appears to be haphazard.
Conversely, neural damage in the brain caused by strokes or tumors
produces visual field loss that is almost identical for each eye, which
supports the idea that the entire degenerative process in glaucoma must
occur at random in the individual eye—without brain involvement.
as previously disabled optic nerve axons recover, the remaining areas
of permanent visual loss in one eye coincide with the areas that remain
functional in the other eye. That is, the team found that the visual
field of the two eyes fit together like a jigsaw puzzle, resulting in
much better vision with both eyes open than could possibly arise by
“The extent and statistical strength of the jigsaw effect in
conserving the binocular visual field among the clinical population
turned out to be remarkably strong,” says author William Eric Sponsel,
MD, of the University of Texas at San Antonio. “The entire phenomenon
appears to be under the meticulous control of the brain.”
Sponsel further explains: “As age and other insults to ocular health
take their toll on each eye, discrete bundles of the small axons within
the larger optic nerve are sacrificed so the rest of the axons can
continue to carry sight information to the brain. This quiet,
intentional sacrifice of some wires to save the rest, when there are
decreasing resources to support them all, is analogous to pruning some
of the limbs on a stressed fruit tree so the other branches can continue
to bear healthy fruit.”
This research is the first evidence in
humans that the brain plays a part in “pruning” optic nerve axon cells.
According to the researchers, this process in glaucoma—apoptosis—is
remarkably similar to the apoptotic mechanism that operates in the
brains of people with Alzheimer’s disease.
“If the brain is actively
trying to maintain the best binocular field, and not just producing the
jigsaw effect accidentally, that would imply some neuroprotective
substance is at work preventing unwanted pruning,” says the study’s
coauthor Ted Maddess, PhD, of the ARC Centre of Excellence in Vision
Science, Australian National University. “Since glaucoma has much in
common with other important neurodegenerative disorders, our research
may say something generally about connections of other nerves within the
brain and what controls their maintenance.”
Dr. Sponsel foresees how
this research can soon translate to clinical use. “It would be
relatively straightforward to modify existing equipment to allow for the
performance of simultaneous binocular visual fields, in addition to
standard right eye and left eye testing,” he says.
Groth SL, Satsangi N, et al. Refined data analysis provides clinical
evidence for central nervous system control of chronic glaucomatous
neurodegeneration. Transl Vis Sci Technol. 2014 May 6;3(3):1.