Herring Gull - eye problem

I have an adult Herring Gull that sits at my window every day. It appears to have some sort of growth overhanging its left eye - about the size of a pea - blue grey in colour. The eye is brown and bloodshot

Its not clear whether this is a part of the bird (damage from a fight or an ailment) or whether this is some sort of nasty parasite

The eye does seem to be functioning but the appendage is progressively getting larger and if it continues the eye will be completely obscured. Not sure what its chances of survival would be with one eye

Can anyone please cast some light on what this is, and what could feasibly be done to help!

Thank you