It would help to see the figure, but some time-tested ways are:
1. Paint the lenses black or a darker version of the helmut color (if on a helmut), then use a gloss coat to give some shine - not too much though.
2. Drop a little super glue or epoxy into the lense area if you need to fill in some space. Often that's all you need to do.
3. There's a few car modeling products that might help, but perhaps someone else here can talk about them.