The first thing I notice is that her pupils seem quite dialated, despite the lighting. Do her pupils react to light at all?
You mention vision problems. How limited is this hen's vision? Is it possible she is blind or almost blind? Has she been like this from the start when you acquired them or did this develop later?
Second; you mention further on that she isn't eating but drinking. It's important that she begins to eat, but it's extremely important to get electrolytes with vitamins for poultry into her system. If she is drinking, I'm wondering if it's not more pertinent to add this to her water so she gets immediate uptake.
I also agree that getting a complete food like chick starter as
@Wyorp Rock suggested is the best food to get her eating since it is fortified with what she requires in her diet when she is this vulnerable state. Checking the crop and finding out if it is working properly is also important. Until she is fully functional and eating, that's where access to electrolytes and vitamins is important to give her energy and balance so she isn't deficient.
When was she treated for coccidiosis? Immediately or later on? Is she still being treated?