This sounds like Mycoplasma. Symptoms include seeing foam or bubbles in the corner of the bird's eye which is later followed by rattles in the chest, swollen sinuses and respiratory distress. Treatment is antibiotics prescribed by your veterinary surgeon. The bird MUST be kept quarantined and kept warm.
This disease is very contagious and easily transmitted by wild birds, on your boots, equipment and on your clothing.
If your chicken does have this disease, they will remain carriers of the disease and will need to remain quarantined from the rest of the flock.