I was going to reply with the following:
When mononuclear infiltrates are found in the iris, the affected iris turns a pale tan to grey color instead of usual yellow and this is known as ocular lymphoma or "grey eye".
To me it is the color change more than irregularity that is the real telling factor. In neither of the examples below is the pupil truly irregular.
@RoyalChick I don't think I would put too much stock in diagnosing Marek's via just an irregular pupil. Supposedly the blood test for Marek's is very inexpensive. Next time you take her to the vet, ask them to test for it.