the sunglasses structure comprises a front piece , an arm hinged to each end of the front piece , and a one - piece lens supported by the front piece . a milling is formed in the lens which is substantially v - shaped , with inwardly protruding coupling elements . a v - shaped elastically deformable bridge is insertable into the milling . the bridge has a perimetral groove for accommodating a perimetral portion of the milling and a plurality of seats accommodating the coupling elements , which snap into engagement with the seats upon inserting bridge into the milling . air vents are provided at a lateral portion of the lens for preventing misting .