The tendency for moisture to condense on the inner surface of eyeglass lenses, often referred to as "fogging over", is a common problem. The condition may occur on any type of eyeglass. However, it is of particular concern in connection with sunglasses and goggles.
The problem may be aggravated in the case of sunglasses and goggles if special shielding against sun, glare, or wind is provided. The special shielding may take the form of side shields and/or top shields that extend rearwardly from the frame. While effective in controlling wind or glare, such shields frequently aggravate fogging by shutting off air circulation between the lens and the wearer's face.
Accordingly, numerous special venting systems have been proposed. However, these proposals have not fully resolved the problem, and, hence, have not been widely adopted.