Eye problems in livestock can be caused by foreign material. One of the more challenging problems is burdock slivers, according to Heather Smith Thomas. A tenacious and invasive weed, burdock is readily spread to new areas by burrs stuck to animals or clothing. When ripe, the burrs release hundreds of microscopic barbed slivers that contain tiny seeds. If a sliver gets into an eye, it can cause inflammation and infection.
In dogs, burrs easily get tangled in coats while barbs can cause issues in the mouth and gastric system.
Source: Countryside Magazine, September 9, 2019. Link. Burrs occasionally get baled up in hay or straw. When the burrs get broken up and float around in the air (if the animal shakes it up, or it blows in the wind), tiny slivers can end up in the eyes.
Also see: There are dozens of articles on how to remove ripe burr pods from coats. Burrs were the inspiration for Velcro. The roots are edible and burdock is found in many food supplements.