Actually, the Black Necked Swan looks like it had cataracts which can cause blindness. The cygnets eyes look like an injury or infection. Yes, lead poisoning and moldy food can cause extreme illness even death, but not necessarily blindness. And, yes, waterfowl can be affected by Marek's disease.

There could even be some type of poison/chemical in the pond that is causing the condition. Have you had the water tested?

If you keep poultry and have a veterinarian that looks after poultry, he/she should be able to treat the swans as waterfowl are sometimes treated as poultry.

We would agree that the best diagnosis would be through necropsy. You may have to send the carcass to a state veterinary diagnostic laboratory, most likely in Lexington or the state capitol Frankfort. The Regal Swan