My chicken has gone blind. Why?

[chickflick]

I have a SLW, maybe 2 years old. I started noticing that she's having trouble seeing. Seems she can see some, maybe shapes and shadows. She knows when I'm out there and runs to me. She follows the other chickens around some. Can get to the front of the house and back and into the coop. She waits for me to put her on the roost at night. Her depth perception is way off. Her pupils are very tiny. Can anyone tell me why this may have happened?

 

[BrattishTaz]

Can you see any cloudiness (cateracts) on her eyes? Head trauma maybe?

 

[chickflick]

Can't see any cloudiness. I'm telling you, her pupils are very tiny now. Could be head trauma, but wouldn't know what happened.

 

[tinychicky]

do you have a picture? it might help

 

[BrattishTaz]

Have you checked to see if her pupils dilate when you move her to a low light area?