cloudy INSIDE low beam lens

Hi all I'm new, and just bought a 2010 Prius. I discover that the "lens" of the passenger side low beams is milky/cloudy, and the light from that bulb is quite dim. I'm not talking about the plastic on the outside getting cloudy, but the round (glass?) lens on the inside. I've replaced the bulb, but I believe the light from that side is still significantly dimmer. The contrast with the driver side lens is dramatic. Driver's side is crystal clear. Any idea if the lens is just dirty? How it got dirty? How to clean it? Or is it maybe plastic and has gotten discolored for some reason ? I've looked up dozens of YouTube videos, but they all talk about the plastic outer cover, not the inner lens. The seal around the bulb housing is intact. I am considering whether at some point in the past both headlights had this issue, and the previous owner might have replaced the entire drivers driver's side headlight assembly, but not the passenger side's.