1000% what goneriding said.
My mare's eyes used to constantly water during the summer and I thought it was from flies irritating her. Turns out that she has ERU [Moon Blindness] and by leaving her untreated, I inadvertently 'helped' her become more blind.
There was a point, about 2 years ago, where one of her eyes suddenly became very watery and swollen. I assumed it was "run of the mill" eye stuff and left it for a day before calling the vet. Once the vet came out, we discovered her ERU, and she was started on treatment.
However, thanks to the single day I waited before getting the vet out, Lacey is now at least 90% blind in that eye that swelled up.
I even posted on this forum the day her eye swelled up, got advice to call the vet asap, and was like "psh, you worrywarts! I'll give it a day. She'll be fine."
And she was not fine. Alive? Yes. But worse off due to the day I took to 'wait and see'? Yes.
Not saying that your guy[s] have anything like ERU -it's probably something simple+small with them- but eye issues are really serious business.
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.