The most visible sign of the disease is an eye infection. Birds in this condition obviously have trouble feeding. You might see them staying on the ground, under the feeder, trying to find seeds. If the infected bird dies, it is usually not from the conjunctivitis itself, but rather from starvation, exposure, or predation as a result of not being able to see.
Avian pox is another common disease that affects a bird's eyes.
This disease causes warty lesions on the head, legs, and feet rather than red, oozy ones, but cannot always be easily distinguished from conjunctivitis. Avian pox is transmitted by biting insects, so it's not usually a problem for birds when temperatures go below freezing. Just as with conjunctivitis, the infected bird becomes vulnerable to predation, starvation, or exposure. Although affected wild birds have swollen eyes, the disease is actually a respiratory infection. The infection poses no known health threat to humans and, until this outbreak, had not been reported in songbirds.