Either decision could be the right decision. If it were my horse I would have him see an ophthalmologist. I had a horse go partially blind in one eye, my reg vet diagnosed the issue and I got a second opinion from the specialist. The vet who is a fantastic well regarded vet completely misdiagnosed him. The specialist said that there is limited training on eyes in vet school and she had basically studied them, just eyes, for an additional 2 years. Same with lameness your money is better spend just going straight to the lameness specialist who looks at it all day. For peace of mind Iād get that second opinion. They could look in the other eye and tell that uevitis is starting so surgery wouldnāt be a kind option. Or they could even have something else to treat the bad eye to avoid surgery.
Is one of your drops blood serum? Iām not sure if thereās any contraindications specific to uveitis, but it seems to improve comfort for normal corneal ulcers. And you can maybe get a larger amount spun so you can just sort of spray it in, instead of trying to accurately place it.
Like it or not, finances figure into decisions like this. Sometimes the money for specialists and extensive procedures ( which also are not always available without overnight travel) is just not there or cannot be justified when the prognosis is iffy.
No need to feel guilty when thats the case and money is better spent on a healthier horse that can be helped with simple groceries and better basic care. Lord knows theres enough of them out there looking for just that.
We had an Appy x with uveitis. She was very spooky and reactive until the eye was removed. Now sheās back to her original confident, laid back self. That being said, I personally donāt think either decision is wrong.
I have a horse blind in one eye. Heās still a wonderful riding horse. I would also encourage you to Google Endo the Blind. He is totally blind after having BOTH his eyes removed. Anything is possible if you are willing to try. 
This. You have gone the distance with this horse OP.
Iād think the odds of the other eye getting uveitis is high. You would have to factor in whether or not the horse would adapt successfully to blindness. You canāt really determine that until it actually happens.
When they donāt adapt, it can be a traumatic and horrific situation. I have first hand experience with a horse who lost her mind when she suddenly went completely blind from uveitis. It was such a bad experience that if I ever had another horse diagnosed with recurrent uveitis, I would euthanize.
OP, Iām so sorry you are going through this.
If it makes you feel any better, Iām facing a very similar situation with an eye issue in a high maintenance retiree. It sucks. Iām not ready to let go, neither is the horse. But she isnāt tolerating compromised vision well. 
I would suspect the outcome might be dependent on the horses age. I boarded with someone who had to enucleate her 3-4 year old horse and her horse went happily to FEI over time. Many horses adjust, but Iām not sure if yours will (I donāt know the situation). I think much depends on their attitude and adjustibility. My friend showed the horse to FEI and now breed her.
He wasnāt a happy horse before these issues. He wonāt be a happy horse afterward. Itās ok to say enough and let him go.
Saw this on boredpanda, might make treatment easier
This Bra Used To Protect A Horseās Infected Eye, Whilst Also Allowing It To See
Dear OP, nothing is easy, is it?
We just had one of ours down to New Bolton to have his eye removed. He developed uveitis in his right eye and it had begun to fill with pus. No trauma or any other signs of injury. We are blessed to have such an amazing hospital within a 30min drive from us, so my vet suggested to take him there immediately. He stayed a few nights while they got it under control and sent us home with meds. On his follow up appointment, they determined the eye (which looked amazing btw) was non reactive to light and non-visual. He also had developed an ulcer and while doing an ultrasound, discovered the retinal had detached. We opted to remove the eye right then an there. He came home the same day and recovery was non-eventful. We kept him quiet for one day on stall rest and then we let him out in a small paddock where he could see the other horses. After another day, it was obvious he wanted out and feared he would do worse damage being isolated so we turned him out in his field.
He wears the Equi-Visor when out, even at night. His other eye gets ointment once a day as a preventative and we are hoping for the best. He is happy and was back to his normal work within a few days with no residual effects.
Whatever you decide, you have to do what you think is best for you and your horse, with the financial and personal considered. No one can fault you for either decision and I only wish you the best in whatever you decide.
I agree with the folks saying that either option is sound and reasonable. My beloved first horse had a problem eye his entire life that we eventually had removed when it became a constant bother to him. It was a quick recovery and he adjusted almost immediately. I almost wish we had removed it sooner. That said, he was a very calm, trusting, and polite horse who was well past the age of high energy misadventures. If you sense that this particular horse would be stressed by the loss of the eye, there is a good risk of the other eye losing vision, or the financial aspect doesnāt add up, then euthanasia might be the best option for you and the horse. I donāt envy you having to make this choice <3
I had a horse with a similar story. While removing her eye was an uneventful surgery, she never really adjusted to it. I lost her to colic 5 months after the surgery.
If I could do it again, Iād opt to euthanise straight up. She was a troubled case to begin with and I feel like I just prolonged and added to her stress in life.
I euthanized a horse with uveitis. He got it in one eye, and went blind in that eye but handled it just fine and that ended the flare-ups. A few years later, the other eye was affected. Flare-ups made him blind in that eye, and he did NOT handle it well at all. He was becoming a danger to himself and others, and was miserable most of the time. He was only 17 and otherwise perfectly healthy, but it was time for him to go.
