Exercise may slow diseases that cause blindness

A new study suggests aerobic exercise may slow
the progression of diseases that destroy the
retina and eventually cause blindness. In mice
exposed to harmful bright lights, the ones that
had regularly run on treadmills had much better
function in their retinas than mice that had not
been exercising.
The researchers suggest the findings, which they
report in The Journal of
Neuroscience , point to exercise as a possible
treatment for slowing down human eye diseases
like age-related macular degeneration (AMD), a
leading cause of blindness in the elderly.
AMD results when photoreceptors - nerve cells
that sense light - in the retina at the back of the
eye start to die.
According to the American Academy of
Ophthalmology, more than 2 million Americans
age 50 and over have advanced AMD, the stage
that can lead to severe vision impairment.
Although both animal and human studies have
suggested exercise may slow down the progress
of neurodegenerative diseases or injury, there is
little information about how it might affect vision.
It has also been suggested that aerobic exercise
works by stimulating a protein called brain-
derived neurotrophic factor (BDNF), which helps
brain cells grow and stay healthy.
In this new study, Dr. Machelle Pardue and
colleagues, from the Atlanta VA Center for Visual
and Neurocognitive Rehabilitation and Emory
University, test the effect of aerobic exercise on
retinal cells undergoing degeneration.
Exercise reduced loss of light -sensing cells in
mice
They worked with two groups of mice, an exercise
group and a non-exercise group. The exercise
group ran on treadmills for an hour a day on 5
days per week for 2 weeks, while the non-exercise
group was placed on stationary treadmills during
the same periods.
After 2 weeks of exercise, some mice from both
groups were exposed to very bright lights (bright
enough to damage their retinas) for 4 hours, and
the others were exposed to dim lights.
The bright lights "caused 75% loss of both retinal
function and photoreceptor numbers," note the
researchers.
"However," they write, "exercised mice exposed to
bright light had 2 times greater retinal function
and photoreceptor nuclei than inactive mice
exposed to bright light."
Plus, they found the exercised mice had 20%
higher levels of BDNF protein than the non-
exercised mice.
Exercise protects the retina, probably by raising
levels of BDNF
To test whether it was BDNF that was mediating
the effect of exercise, the researchers injected the
mice with a drug that blocked the protein. They
found it reduced retinal function and
photoreceptor counts in the exercised mice to
"inactive levels."
The researchers conclude their findings "suggest
that aerobic exercise is neuroprotective for retinal
degeneration and that this effect is mediated by
BDNF signaling."
Dr. Pardue says: