I am worried about a chicken that I recently acquired from a neighbour who lives about 800 metres away. She was bought four point of lay pullets by her family two years ago, because she'd "always had a dream of keeping chickens". She very quickly found that four was two many for her, and gave two away to another neighbour. She kept these two until just after christmas, when I called in to see her. She was complaining that it was too much work for her (she's 80), and when I went to see them they were in a small muddy pen, being given food scraps and a cup of seeds a day. (She had stopped letting them free range in the garden because of the mess.) I have seen them on and off over the past two years, and they have always seemed in good health (no sneezing, diarrhea etc), so I considered them to have been 'quarantined' from my flock, and agreed to take them off her hands. They have both settled in really well, but the day after they arrived I noticed that one of them has a 'keyhole' pupil in her right eye. The round part of the pupil doesn't seem to react to light - it always stays small - but the elongated part seems more like a smudge on the iris than an actual hole or deformation. Also, the iris hasn't changed colour - it is still orangey-brown. Her other eye is perfectly normal. It doesn't seem to bother her at all - she has no problem seeing to eat, she can pick up grains etc. without any problem at all, and has been named 'BraveHeart' because she has managed to work her way up the pecking order in a very short space of time! It could be that she was born with this eye, and that I just never saw it when I visited previously. However, looking online I have seen that this type of pupil can also be a symptom of ocular Marek's, but I'm not certain if my chicken's pupil is really the same as the images that I have seen. Also, although there is lots of information about Marek's in general (including Nambroth's wonderful thread here on BYC - https://www.backyardchickens.com/a/the-great-big-giant-mareks-disease-faq ), I can't find a lot of detail about ocular Marek's. She doesn't show any other symptoms at all, and her sister is fine. Even if this is ocular Marek's, does this mean she may go on to develop other symptoms, or does the ocular version just stop at the eye, and not result in all the other neurological / cancerous problems? Any ideas or advice are welcome.