As Michael J. Fox nears the 30-year anniversary of his Parkinson's diagnosis, the actor-turned-activist is opening up about how the experience has changed him.

Fox previously told "Good Morning America" after a fall in 2018, he had surgery and needed to relearn how to walk.

In a new interview with AARP the Magazine, Fox said that the episode led him into "darkness" -- and then out the other side. "I started to notice things I was grateful for ... I concluded that gratitude makes optimism sustainable," he said.

Fox officially retired from acting in 2020, when, "I reached the point where I couldn't rely on my ability to speak on any given day, which meant I couldn't act comfortably at all anymore. So, last year I gave it up," he explained.

The actor, 60, remains a tireless advocate for Parkinson's research through his foundation. "We created what has become this giant network of patients, scientists and institutions. We've put more than a billion dollars into it," he said.

When asked about seeing a cure in his lifetime, Fox says he's "blunt" about it. "I'm 60 years old, and science is hard. So, no."

That still hasn't dampened his optimism, however. Fox said watching, of all things, the fan-favorite "Back to the Future" also taught him to lighten up.

"I came across it on TV last Christmas. And I thought I was really good in it, better than I thought I'd been," he said. "More important, I got the spirit of the movie. I understood ... that we all need ... to take credit for what we've done and the lives we've touched and to occasionally step back a bit and appreciate that much of life has been great and that there's a lot more to live."