Why is my hen's head turning sideways?

[rocketdog]

I have a very nice buff Orpington hen whose feathers have never been full since I got her, they start growing back, then fall out again. She still lays some eggs, not often, but she's a nice girl. I put Pic-No-More and blu-cote on her and treated her for lice, but recently her head has been going sideways like she is watching the sky, but she isn't. Does anyone know what would cause this?

 

[englishcockers]

I have one who does this. She's blind in one eye. When startled, she spins.
This may or may not be a vision issue with your hen.