Regular walking may protect the eyes and help prevent age-related vision loss, research has suggested.
Tests on mice showed that moderate exercise slows down the death of light-sensitive retinal cells.
Scientists believe the discovery has important implications for age-related macular degeneration, the leading cause of blindness in the elderly.
"This research may lead to tailored exercise regimens or combination therapies in treatments of retinal degenerative diseases," said lead researcher Dr Machelle Pardue, from Emory Eye Centre in Atlanta, Georgia, United States.
"Possibly in the near future, ophthalmologists could be prescribing exercise as a low-cost intervention to delay vision loss."
Macular degeneration is caused by the death of photoreceptors in the retina, the digital "camera" at the back of the eye which turns light signals into nerve impulses.
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Dr Pardue's team studied mice that ran on a treadmill for two weeks before and after being exposed to bright light to trigger retinal cell loss and mimic the effects of the disease.
Exercised animals ended up with nearly twice as many photoreceptors as mice which spent the same amount of time on stationary treadmill.
Their retinal cells were also more responsive to light.
"One point to emphasise is that the exercise the animals engaged in is really comparable to a brisk walk," Dr Pardue pointed out.
"One previous study that examined the effects of exercise on vision in humans had examined a select group of long distance runners. Our results suggest it's possible to attain these effects with more moderate exercise."
The benefits of exercise to vision partly stem from a growth factor protein called BDNF, the researchers believe.
Mice running in the treadmill had higher levels of BDNF in the blood, brain and retina.
When the protein's activity was chemically blocked, it cancelled out the protective effect.
The team, whose findings are reported in the Journal of Neuroscience, is now looking to see if exercise can also help combat other retinal diseases such as glaucoma and diabetic retinopathy.