"I'm learning that one minute you can be fine, and the next I went blind in my right eye," he said Tuesday on The Talk. "It’s a completely unpredictable disease."
Osbourne, 26, who also discusses his shocking diagnosis in this week's issue of PEOPLE, says he got 80 percent of his right-eye vision back.
"They don't know if it will ever improve beyond that, but everyone’s different," he says on The Talk, which is co-hosted by his mother Sharon Osbourne.
That means he simply doesn't know what will happen to him.
Joining Osbourne on the show was fiancée Lisa Stelly, who says that parenthood helps put things in perspective.
"We are really trying to stay positive," she says. "We have diapers to change and a little girl to look at and smile at."
For all the details of Jack's shocking diagnosis, a candid interview with Jack and Sharon, and more on how the famous family is coping, pick up next week's issue of PEOPLE, on newsstands Friday
To get a sneak peek of this week's issue click here