I am not a vet. The white spots you are talking about are on his iris (the brown part) so that wouldn’t be a cataract. A cataract would be seen as a clouding of the dark “hole” in the iris. Regardless, he is showing some signs of eye issues so having him examined is a great idea. Just to give you a bit of optimism, my mare is blind in one eye but we don’t have many issues because of that and I am far from a pro rider, I am a middle aged novice. We even jump (tiny jumps, because of me). Best of luck.