Swollen eyes like this are due to the start of a respiratory infection. There are many different respiratory diseases that can cause this, most common being Mycoplasma Gallisepticum (MG/CRD). Other diseases that could (less likely) cause this are Infectious Coryza, Infectious Bronchitis Virus, Infectious Laryngotracheitis Virus, Aspergillosis and Fowl Pox. To me, this looks like to could be a mild start of MG or Fowl Pox. MG is a bacterial infection of poultry affecting the respiratory tract, primarily attacking the sinus, trachea and lung areas. The MG bacteria is incurable, but treatable with antibiotics. This bacteria is chronic, meaning it’ll come back within times of stress. All birds that seem to have “recover” are asymptomatic carriers of the bacteria, shedding the MG bacteria in their feathers, feces, dander, respiratory secretions and other bodily fluids. The MG bacteria can also be spread from infected parents through the egg of a developing embryo, making any chicks that happen to hatch, already hatch with this bacteria.
Fowl Pox is a viral infection of poultry, resulting in scabby, painful lesions. There are 2 different strains of this disease, wet and dry. Wet fowl pox can cause respiratory symptoms along with cheesy like lesions to form inside the mouth, nares, eyes, trachea, throat, combs, waddles and earlobes, making it hard for the bird is breathe. Dry fowl pox starts with these lesions that start off small and then eventually get bigger and pop up around the chickens faces, comb, waddles, earlobes and (sometimes) legs and feet. Since this disease is viral, there are currently no cures or treatments for it.This is a case where supportive care for birds infected with fowl pox would be needed, while the virus runs its course. Any scabs that fall of the birds, are contagious, so through cleaning is recommended. Fowl pox can be transmitted from infected mosquitoes or carriers in by rats, wild birds and/or mice.
Here is more information about MG:
https://afarmgirlinthemaking.com/respiratory-conditions-poultry-mycoplasma-in-chickens/
Here’s more information about Fowl Pox:
http://extension.msstate.edu/publications/fowl-pox-backyard-flocks
Before treating with anything, I highly recommend that you get your birds tested to find out which disease is causing the symptoms. You can get them tested here:
https://www.zoologix.com/avian/index.htm
Or
http://www.vetdna.com