Help! Just caught hen with eye issue graphic pic
There is probably a large glob of puss inside the tissue surrounding the eye from a sinus infection that may have been caused by coryza or another bacteria. You will need to get some tweezers, QTips, cotton, and saline to go to work on cleaning out the yellow gunk. It will take an extra pair of hands, and wrapping her in a towel may help. Once you get the eye cleaned out, rinse it saline, and apply either Terramycin eye ointment, Vetericyn eye gel, or even plain Neosporin ointment twice a day. If it is coryza, she may have thick nasal drainage and a bad odor. Antibiotics such as Sulmet, Sulfadimethoxine (Dimethox) and Tylan are sometimes used to treat it. It can cause other chickens to be carriers or make them sick.
Here are a couple of threads that have similar pus removal info: