It's hard to tell, are there bubbles in the eyes?
Any coughing, sneezing, wheezing?
Since it is spreading, you may want to separate them from any others that are not showing symptoms at this time. Respiratory illnesses can spread through mucous/discharge, dust, dander among other things.
It could be a respiratory illness like Mycoplasma Gallisepticum (MG).
You can flush the eyes with saline and apply some Vetericyn eye gel or Terramycin eye ointment a couple of times a days to help with any secondary infection in the eyes.
You can also treat with antibiotics like Tylan Soluble Powder or Oxytetracycline. Keep in mind that antibiotics may help with relief/support care and help with secondary infections, but once recovered, birds still remain carriers for life.
"Tylan is 1 tsp per gallon of water for 3-5 days. The oxytetracycline dosage can vary with the brand, so just search for the dosage if you chose that."
(reference post#2 http://www.backyardchickens.com/t/1086681/is-this-the-flu-or-a-serious-disease)
Here is a list of common respiratory illnesses (symptoms chart is at the bottom of the link page)
Edited by Wyorp Rock - 6/8/16 at 11:24pm