Rupert Grint covered his left eye with his hand and attempted to read the top few lines. “E, D, F, C, E, F,” he said slowly.

“Close!” said Marilyn Blumengold, a sales associate at Moscot, the eyewear shop on the Lower East Side.

This was on a recent snowy afternoon. Mr. Grint, currently shooting the fourth season of the Apple TV+ horror drama “Servant,” had driven in for the weekend from his temporary home in Philadelphia to take in the sights and maybe also have his eyes checked. He had noticed a blur in the right one, he said.

But Moscot, which has been in business for more than 100 years, didn’t have an optometrist on-site on Sundays, so Mr. Grint, 33, improvised his own test, standing about 20 feet away from an eye chart at the back of the store.

“Almost 20/20,” Ms. Blumengold said encouragingly.

Satisfied for the moment, Mr. Grint turned his attention to picking an eyeglass frame, moving through the store shyly, unassumingly, never asking for help, but also never declining it.

“I’m a very private person, an introvert,” he said. He slouched through the store in a black Issey Miyake suit that a stylist had picked out for the outing. “Strange pajamas,” he called them. “Surprisingly, I think they look good.” His red hair flopped over the top of some frames.

Mr. Grint seemed overwhelmed. “There’s just so much choice,” he said, as he surveyed the rows of display cases. He said it twice. “It’s quite ‘Harry Potter,’” he added without any prompting. “Like choosing a wand.”

Mr. Grint should know. He starred as Ron Weasley in all eight “Harry Potter” films. (Ron’s wand? Willow. With a core of unicorn hair.) Ms. Blumengold may or may not have known that — at one point she steered him toward a pair of round black glasses, a $300 model called the Zolman, which looked very Harry-esque.

“No,” Mr. Grint said politely.

When the “Harry Potter” films ended, Mr. Grint was worried that he may not make it as an adult actor. He knew how to play Ron, Harry’s brave, anxious sidekick. He didn’t know if he could play anyone else. “I definitely did think, ‘Is it too late to pick something else?’” he said.

He bought a pink-and-white ice cream van, which he drove back to his family home just north of London on his last day of shooting. He thought briefly that he could make a go of that.

But after taking a year off, he tried acting again. He had been sent a lot of “Potter” adjacent material — more sidekicks — but he held on for edgier, more serious, more adult work. He took a part in a Jez Butterworth play, enjoying the discipline of theater, and starred in the Crackle crime dramedy “Snatch.”

His most significant post-“Potter” role has been in M. Night Shyamalan’s “Servant,” a creepy drama on Apple TV+ about a Philadelphia couple who hire a nanny to care for a baby that is actually a therapy doll. (The real baby had died in an accident.) Mr. Grint plays Julian, the baby’s supercilious uncle. “It’s quite a difficult subject, especially if you’ve got a baby,” he said.

Halfway through the series, in the spring of 2020, his partner, the actress Georgia Groome, gave birth to their daughter, Wednesday G. Grint. “Having a child midway through definitely made me understand what a loss that would be,” he said.

Wednesday had made him into a bit of a hypochondriac, he added. (Working on a show in which terrible things happen to bodies in nearly every episode — self-harm, self-flagellation, being buried alive — probably hasn’t helped.)

“That’s why I wanted to have an eye test,” he said. “I’m slowly becoming more aware that there’s lots of moving parts in the body.”

This season’s finale airs on March 25, but Mr. Grint has already begun filming the show’s fourth and final season. And, no, he has no idea what the twist will be. “It’s quite a thrill to work that way.” (It must be. He has signed on for Mr. Shyamalan’s next film, “Knock at the Cabin.”)

Ms. Blumengold started him off with a classic Moscot model, the Lemtosh, a brown acetate oval frame with a slight 1950s vibe. Many of the frames have Yiddish names, though “Lemtosh” just sounds like one. Mr. Grint looked confused as he squinted at himself in the mirror. “It changes your appearance,” he said. “It changes your personality.” Into what, he wasn’t sure. But he felt that he could already see a bit better.

“Very nice,” Ms. Blumengold said. “Very handsome.”

Then he tried on a dozen more acetate frames, toggling between rounder models including the Genug (Yiddish for “enough”) and Frankie, and rectangular ones like Kitzel (“tickle”) and Shindig, a retro unisex model. Most cost around $300.

“I do struggle with making decisions,” he said. “It’s quite a responsibility, choosing.”

After 40 minutes, he settled on the Yukel (“buffoon”) a clubmaster style with a thick tortoiseshell browline and a thinner gunmetal bottom.

Ms. Blumengold created a customer profile and added it to his file, in case he does end up needing eyeglasses. He could always call in his eye test results and have the glasses made.

But Mr. Grint didn’t want to leave empty-handed, so he set his sights on the sunglasses. After flirting with the Boychik (a term of endearment for a little boy), he turned back to the Lemtosh, this one in brown acetate frames and dark brown lens. After all, Mr. Grint is now a man.

As he waited for Ms. Blumengold to box the glasses up, he popped outside for a quick vape hit. When he returned, she handed him a chamois cloth to clean them with. “This is your last Yiddish word for the day,” she said. “‘Shmatte,’ a rag.”