If your vet suspects that uveitis is imminent, trust him to know. I have a 32-yo Appy gelding with only one eye, and the vet is positive that his frequent corneal ulcers are a result of incipient uveitis that just has never quite blossomed but keeps his eye just a bit irritated.
But that’s not the problem with your gelding. Whatever caused the spook is up to your judgment, but the bucking is a problem that is only partially related. Now, you’re saying that you lose your seat when he spooks, and that could cause the bucking (or give him a real good excuse for it). Do you have a bucking strap on your saddle? It’s a cheap and easy fix. Some tack catalogs call it a “grab strap”, but regardless of the name, it’s a simple leather strap that buckles to the saddle across the front of the pommel. If you’re riding Western, you have the horn, so you don’t need a strap. Get in the habit of putting your PALM against the horn and pushing hard down so that your butt goes deep into the saddle seat. Don’t wrap your hand around the horn and pull, as that’ll throw you forward and out of the saddle. If you’re riding English, put a strap on the D rings at the front of the saddle, and get in the habit of grabbing is and sitting upright with your heels down when he spooks. Every time! You’ll make your seat more solid, and if you’re balanced you can control his forward motion to get his head up so he can’t buck. That will help break him of the habit.
Horses In the Yard