This year, we have started to notice House Finches with conjunctivitis at our feeders. We clean the feeders regularly. Today, two different males are in distress, the one with the worst infection shown below just after it was chased off of the feeder to land on the fence.
In addition to not flying straight, often trying to hover in place while slowly drifting towards the ground, the infected birds repeatedly rub the sides of their heads as this one is doing.
Some more information about the condition provided by University of Cornell.