I have noticed that there are what appear to be two versions of the headlights on this generation Prius. In the first the upper compartment lens has a sort of cut glass like look to it, with parallel lines maybe 3/4" of inch apart running from the top of the headlight to the bottom of the top compartment. In the second the upper compartment is just smooth plastic, with no lines like that. In the second the silvery reflector inside has vertical troughs along the walls, presumably to focus the light forward and out. Not sure about the first variant because I have not seen one that wasn't foggy. Is one of these OEM and the other aftermarket, or did Toyota ship two different versions? Maybe one for the Halogen bulbs and one for the HIDs (even though they would be in the lower compartment, which seems to be the same in both variants).
The owners of those other cars might not appreciate me pulling a headlight out of their vehicle to inspect its underside! The attachment is from a post on Ebay, it clearly shows the "cut glass" region over the upper chamber. It is described as an OEM part for a Xenon headlight. No part number in the post though.