If you have a flock of ducks of any age that seem to have eye problems, it is probably because of ammonia in the air.
At some point in their day, they are locked up in an area of inadequate ventilation and excessive manure.
The ammonia from the manure settles at the lower levels and irritates their eyes and lungs.
If you can smell ammonia in your pens, it has caused damage to your birds and something needs to be done.
Normally it can be cured by better ventilation and drier conditions.
In the winter people are often reluctant to ventilate adequately as they just think all that warm air is heading outside and they have to pay to heat more air.
But if that warm, humid, ammonia laden air stays in your building, it will hurt your birds.
Once you increase ventilation and use more bedding to keep their pen drier, normally the ducks will cure themselves.
However, if the problem was severe, some ducks may be left blind.
To supplement increased ventilation and more bedding, you can also use Iron Sulfate.
This is a fertilizer you can often purchase at your local fertilizer dealer. It is a powder or granular product that you can spread in your bedding.
The iron combines with the ammonia and keeps it from volatizing into a gas.
If you do use the iron sulfate, you will have even a richer material for composting or direct fertilization.
If ammonia is not the cause of your eye problems, dust may be getting in their eyes and injuring them.
The dust can be from feed, roads or the bedding you spread in their pen.