We would get the swan to a veterinarian to check for cataracts or some other defect that could eventually take its eye sight. It is very difficult to make any kind of diagnosis from the photo without seeing into the back of the eye with an opthalmoscope. A veterinarian using this instrument will be able to give you an answer if this is a defect or just a discoloration that this particular swan may carry genetically. Please let us know if you get a diagnosis. The Regal Swan