The glasses harry potter wears are round glasses which contain a black frame and round lenses. This kind of glasses have a retro and unique style, so people who want to follow the fashion and want to look different are trying to get harry potter glasses. This style of eyeglasses have become fashion in recent years and I believe they will be in style for a long time. However, if you have a round face, the style of harry potter glasses can't suit you fine.
The manufacturer who made them was the Algha Works factory (their home brand is Savile Row Eyewear). They're still around it seems! The news (http://www.dailymail.co.uk/news/article-2397428/See-inside-The-Algha-Works-Britains-bespoke-spectacle-frame-factory.html) and their website (http://savileroweyewear.com/shop/warwick) seem to confirm that they were behind the specs.
From his images, i can see that it is a pair of thin and slim round framed glasses. Some people said that's Windsor glasses with black Zylo. Such round eyeglasses are really famous because there are many great person worn it such as John Lennon, Ernest Hemingway, Groucho Marx, Theodore Roosevelt, William Hurt etc. After all these years, this round framed glasses still in the fashion and favored by many celebrities like Lady Gaga. It is really worthy to collect a pair of such classic round glasses.