From the article:

In the current study, the scientists trained mice to run on a treadmill for one hour per day, five days per week, for two weeks. After the animals were exposed to toxic bright light – a commonly used model of retinal degeneration – they exercised for two more weeks. The exercised animals lost only half the number of photoreceptor cells as animals that spent the equivalent amount of time on a stationary treadmill.

Additionally, the retinal cells of exercised mice were more responsive to light and had higher levels of a growth- and health-promoting protein called brain-derived neurotrophic factor (BDNF), which previous studies have linked to the beneficial effects of exercise. When the scientists blocked the receptors for BDNF in the exercised mice, they discovered that retinal function in the exercised mice was as poor as in the inactive mice, effectively eliminating the protective effects of the aerobic exercise.