eye dilation in cats

my 4 yr old female dsh olivia has been having a problem with her eyes staying dilated at 1st it was barely noticable and in the last month it has only been her right eye and at it seems to stay that way, she still gets around but she also stares off at times in a daze.  her vet said she wasnt sure and that she realy didnt know much as far as the eyes go.  that wasnt very encouraging.  I would like to know if anyone could tell me what might cause this condition or if they have even heard of anything like it.  i am since changing vet and going classical holistic vet.