I cleaned mine today, I tried the toothpaste method first but it only made a slight improvement on the lenses which were opaque (they've been listed as advisory faults a few times on MoTs and got progressively worse as time's gone on), so I tried Mer polish that | had in the garage for about 15 years, it took a couple of go's but came up almost clear, I think a bit more time would have got them perfect.
While I was hard at work, a passing workman told me he'd done his daughter's with a mixture of baking soda and white vinegar, then he showed me before and after photos of them on his phone, the results looked pretty good.
If you haven't used Mer before, it's a bit like T-cut in consistency and can be used as a light cutting paste or as a straightforward polish.