My 3 year old has had a recurrent goopy left eye since I picked him up a month ago. Only left eye. Just seems to produce that white pus that collects down in the corner. I keep it clean, keep it well fly sprayed , he won't keep a fly mask on so I've been through that. I've looked in there and eye is clear and healthy. It's NOT sore , I can rub on it and it's all good. What would cause this ? Allergies? 

Mine have all had it all summer, but no matter how much fly spray I wipe on their eyes theres still 5-6 flies on each eye. I've just left it and wiped it off when I can. Mine won't keep a fly mask on for more than an hour either. They also have weeds in their turnouts that are tall, so could be a weed allergy too. Some of the horses around them have hives that don't go away. We pulled them off the turnouts to spray the weeds with roundup twice, but it didn't do a thing to the weeds. So who knows what the cause is, sometimes I think it's both allergy & then flyies being drawn to the goop making it worse 

Yep. And why only 1 eye. Lol. I will just keep cleaning it to. 

Yeah my mare only has it in one eye, but its also the same eye she fractured the socket of in the front corner. So she always has a little bit of discharge since then. One gelding has it some days, and some days not. And the other is just 24/7 

Clogged duct or allergies? 

My mare had  a watery/gooey right eye last week.  The vet did a nasolacrimal duct flush.  The solution came out her tear ducts in her eye, she looked like she was crying…..  The vet said she had some dried mucus up in her sinus and clogged ducts.  After that treatment the mare’s eye cleared up and has been fine since. 

May have a stopped up tear duct. Might need a flush.

A blocked tear duct. My husband's retired heel horse will get the goop in the summer and in the winter it's teary. We've had him to the vet and they've tried putting a small plastic thread into the duct and it's blocked with scar tissue for a lack of a better term. We put fly masks on him in the summer to keep the flies off, but he tears them off so we just use a little saline about once a week to flush the eye. His vision is unaffected.

Agree with other suggestions to take the horse to the vet to get a nasolacrimal flush. It might clear out "goop" stuck in there. Vet will put in a small syringe in the horse's nose, and the saline will come out the horse's eye. 

Unless.... there is a blockage. I have one horse that on one side, his is just not connected and/or permanently blocked. Vet tried 2 huge syringes one time and nothing ever came out of the eye and it came back out the norse. If that's the case, it is what it is and just do you best to keep the eye as clean as you can.

I was told that mine didn't have tear ducts.  He keeps that eyeball boogers in both eyes but one eye is worse than the other.  But when you fuss at him I swear he has tears that runs out of both eyes.  I just keep them clean and whenever he is hauled he wears a fly mask.  It doesn't seem to bother him and different vets have looked at them and they just suggest to leave them alone and keep them clean.