How about another approach? For 75 mm and 120 mm figures, I've used exposed 35 mm camera film (acetate), cutting it to fit gas mask goggle lenses. If you're working with exposed film it will range in shade from clear to dark amber. So you pick what suits your situation. I used a leather punch on one occasion for a completely round lense and two sizes of metal punches with some careful trimming on another. Right now I'm working with some 120 mm Verlinden accessory glasses and some putty to convert them to ski goggles on a Wurttemberger ski troop Vizefeldwebel. The nice part of the acetate lense is that it kind of stands away from the eyes. I painted the eyes and gas mask of a 75 mm Fusilier WWI figure, then added the lenses and I think it looks realistic.
All the best,
Dan