A good example of a near monopoly (80% market share)

Luxottica produces about 80% of the frames for sun- and eye glasses. Moreover, it has achieved this dominant position with little help from the government, as far as I can tell. Here is an excellent account of the predictable effects: http://www.forbes.com/sites/anaswanson/2014/09/10/meet-the-four-eyed-eight-tentacled-monopoly-that-is-making-your-glasses-so-expensive/.