With a micro-electric fan to circulate air, Smith� Knowledge Turbo <em>OTG</em> <em>Goggles</em> offer eyeglass compatibility and the ultimate in fog-free vision. <em>OTG</em> (over the glasses) design features an enlarged chamber that fits easily over most eyeglasses. Large frame size accommodates a larger face, and fits snugly and comfortably under a helmet. Two-speed micro-electronic fan runs silently and continuously up to 100 hours, drawing air through vents to eliminate fogging. Fan features a high-power mode to clear moisture