History: 2 yr old Red Star hen. Noticed decreased vision 5 days ago. Hen was walking right along fence and bumping into other hens. Isolated her to prevent injury. Difficulty connecting with food in my hand, she would peck into the air. Head movement noticed as well. When she holds her head still it would move backwards. She would have to constantly move her head down to counteract this. 3 days after being isolated vision improved but she cannot stand. Her head movement is still there but much less severe. She can move her legs but from her knees? down she can't. Her toes are curled and have no tone. I've started adding vitamins, electrolytes and probiotics into her water. They all eat Nutrena Laying Pellets that I purchase from Tractor Supply. Normal poop, alert, showing no signs of discomfort or pain. Eyes bright with no redness or drainage. Eating and drinking very well. Other hens are perfectly normal. Have 5 hens and 1 rooster in an enclosed 40'X15' lot. Laying eggs normally. Any ideas? I've not come across anything in my research. Especially not with a chicken as old as 2. Thank you all.