I have an 18month brown leghorn hen that is having some eye issues. Her left eye pupil is not working and dilating and there seems to be vision impairment in that eye only. She won't let people on her left side and seems to be looking at her world from just the right eye. There may or may not be some very slight murkiness/cloudiness to the left eye. Other than her vision, she is acting 100% normal (eating, drinking, laying, interacting with other, etc). Any ideas what causes this?