Arriving in an unmarked car in the late afternoon, the Argentine pontiff visited the shop in the historic and lively city centre close to the famous Piazza del Popolo, drawing crowds outside the window.
He tried on a few frames over a period of about 40 minutes, and according to specialized Vatican news agency I-Media, the pope asked the shopkeeper to charge him the normal price.
"I don't want new frames, you only need to repair the glasses, I don't want to spend," the pope was quoted as saying by the optician Alessandro Spiezia.
Francis, 78, who is long-sighted, had previously been a customer of the shop, as had his predecessor Pope Benedict XVI, according to the optician's website.
In an interview with Mexican television in March, Francis said that since becoming pope in 2013 he missed being able to go anonymously into the streets, to eat pizza for example.
He is renowned for throwing off his security and plunging into the crowds to greet pilgrims, and often uses jokes or stories to spread the values of the Church.