Keyhole / cat's eye pupil - ocular Marek's?

[KayTee]

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.

 

[Eggcessive]

This is very interesting. Most of us jump to the conclusion of any irregular shaped pupil being Mareks disease, but this type of eye defect is very common in humans--my grandson has one eye like that, and it can be associated with other deformities. I am not experienced with Mareks the way Nambroth and some of the others on BYC are, so I will let them answer this. A closer photo would be good.

 

[KayTee]

This is very interesting. Most of us jump to the conclusion of any irregular shaped pupil being Mareks disease, but this type of eye defect is very common in humans--my grandson has one eye like that, and it can be associated with other deformities.

That is my thought too - I know that it can exist as a benign eye condition from birth, but as I only got these girls at two and a half years old, I don't know how long she has had it. (And my neighbour has no idea - she had never looked them that closely!)

A closer photo would be good.

I know, and believe me I've tried, but that was my best effort! They are happy to get under your feet if you are digging for worms, but apart from that it is hard to get within 10 feet of them - they are so skittish! I will see if I can post a cropped version.

 

[KayTee]

Ok - here's a cropped version of the photo. Hopefully you can see the fact that the lower dark part seems to be more of a stain than a hole. What I worry about is that the pupil doesn't seem to react to light at all, although she seems to be able to see well enough anyway.

 

[Eggcessive]

Here is a link for Mareks involving the eyes. The 2 sets of pictures look very different from your chickens's: http://partnersah.vet.cornell.edu/avian-atlas/search/lesion/464

 

[KayTee]

Eggcessive, you're right, those two eyes look very different. The pupil looks more deformed that my girl's. Thanks for the link. I don't feel too worried - nobody's showing any horrible symptoms of anything at the moment, but I always try to be on the lookout, to try and head off problems before they get too bad. (Without being too much of a chicken hypochondriac!)

 

[Eggcessive]

The name of that defect in your chicken's eye is a coloboma. Apparently, it is a common sex-linked defect in chickens and other birds and animals. I found several references on cicken coloboma studies as well as a photographer's collection of "blown eyes" in birds. Here are a couple of the links:
http://connection.ebscohost.com/c/a...ce-elements-candidate-genes-coloboma-mutation
http://onthewingphotography.com/wings/2012/02/27/birds-with-blown-eyes/
http://www.nlm.nih.gov/medlineplus/ency/imagepages/8750.htm

 

[KayTee]

Thanks Eggcessive - that makes me think that it's more than likely a genetic thing. It's quite probable that she was born with it, but my neighbour just never noticed it. Thanks for all your help.

 

[Eggcessive]

Your welcome. I learned something today from this, where I would have thought it was Mareks. I found another case of this on BYC with both eyes affected. It is pretty obvious that it is a coloboma, especially in the other eye: https://www.backyardchickens.com/t/845701/ocular-mareks-any-doubt

 

[ten chicks]

I had a black lab with the same condition,not life threatening or dangerous at all.