Tylan dosage is fairly forgiving. Dosage is 0.25 ml per pound, or about 1.25 ml for a 5 pound hen 3-4 times a day for up to 5 days.. Sorry for my error in dosage earlier, but Tylan can be given as much as 40 mg per Kg 3-4 times a day, so no problem there. Tylosin (Tylan generic) powder for the water dosage is 1 tsp per gallon of water if you ever use that.
I had a hen once who had foam in her eyes at times, then later in the day nothing. It seemed to happen in cold weather. If you should ever lose a bird with symptoms, or even just an unknown cause, your state vet can do a necropsy to do testing and make a diagnosis. That is how some people find out they have a bird or a flock positive for mycoplasma gallisepticum or MG. Most people don’t get tested though. You can then either treat with antibiotics or not. Some cull birds with symptoms to limit exposure. But if you see the symptoms, it is responsible to close your flock.