HARRY Potter was ahead of his time. Round eyeglasses, the distinctive kind worn by the young wizard, are shaping up to be the next big thing in eyewear. Seriously. Over the past decade or so, myopic hipsters have favored rectangular frames. More recently, amusingly oversized sunglasses - a la Jackie O - have become a celebrity mainstay. Now design houses like Paul Smith, Balenciaga, Lunor Eyewear, Theo, and Anne et Valentin are pushing a return to classic round and semi-round frames for spring. “There's definitely a move to more conservative eyewear and vintage shapes,” said Filipa Fino, senior accessories editor at Vogue. “For a while, everything has been oversized. In the sunglass market especially, it was all about overpowering the face. Now, the trend in fashion is to go back to the classics.” Classic with a modern twist, that is. Paul Smith's new Boys Only collection of sleek round frames come in bold colors like orange, royal blue, and translucent gray. Balenciaga, which will roll out its first sunglass line this spring through manufacturer Safilo USA, is showing large round frames reminiscent of looks from the 1970s. They were inspired by sunglasses from the Balenciaga archives, said Eden Wexler, a spokeswoman for Safilo. Robert Marc, a New York-based designer who operates a retail store on Newbury Street, has introduced two modified round (a cross between round and square) frames for the spring, called style 195 and 196, as well as a rounded sunglass frame. The eyeglass frames are available in five colors including smoke gray and chestnut brown. The glasses, which were introduced in October, are a huge hit, Marc said. “It's absolutely taking off. We have an incredible back-order on the 195,” he said. “Every time we get a shipment in, they don't even hit the floor. We have a two- to six-week waiting list.” Marc also believes the country's serious mood translates to a more conservative image. “People are really thinking about things: the economy, the elections, the war, the green movement,” he said. In fashion, that has translated into more retro nerdy looks. “Look at Harry Potter and Ugly Betty. We are celebrating the nerd,” he said. “Wingtip shoes are in fashion again and Thom Brown's very preppy, slim suits. On the streets, there is a desire to have a more intellectual look.” Celebrities are already embracing the bookish look. Bono, the eyewear bellwether who's rarely photographed without sunglasses, was spied recently in France sporting a pair of round frames. Mary Kate Olsen made the scene at the Sundance Film Festival in round frames, too. Larry Leight, founder and creative director of Oliver Peoples, which also designs eyewear for Paul Smith, said he believes the public is bored with rectangular and rimless frames. “They have less character,” he said. “When looks get tired and there's nothing fresh coming out, that's when designers pull out things from the past.” Oliver Peoples, in a nod to its 20th anniversary this year, selected vintage designs from its original collection in 1988. “I wanted something old school,” Leight said. Round eyeglasses, of course, have never been officially off the market. The Anglo American Optical Co. in Illinois and London has been making round frames since 1882. But Allan Caliman, the company's co-owner, concedes that round shapes can be a tough sell. “Round faces can't wear round glasses,” he said. “You need to have a long, slim face. Round glasses are really for the eccentric types who want their glasses to be seen.” This spring, Anglo American has seven round styles in a range of colors from red to yellow to light brown. “They're definitely bold,” said Caliman. For the fashionista who's resistant to the bookkeeper look, Vogue's Fino says take heart. “I think it's all a question of getting used to it,” she said. “In fashion, there are often things we think we'd never wear again and then they pop up on the runway and look new again.” __