Is my boy doomed?

I own this horse since forever, he is almost 11 now. A few years ago he started having eye issues during summer, conjunctivitis according to the vet. It's worsening every year and he is now super intolerant to the sun. We are barely out of winter, the sun is out and he has the same problem. It's becoming more frequent, even with attention and care. Early on, I bought a anti-UV mask and every time there's sun he wears it. My vet keeps saying that it's "just" conjunctivitis but I feel there's more. He's an appaloosa cross with a lot of depigmentation, his eyes are marbled with blue. I know that appaloosas are prone to eye problems but I need advice. I'm going to get a second opinion soon. If there's owners that have the same issues please share your stories. I don't want my boy to be doomed for the rest of his life and loose his sight.